iapennell

Just to add that sea surface temperatures in higher latitudes are modified- over time- by the prevailing weather-patterns over them. If the warmer-than-usual seas cause low-pressure polewards and prevailing mild Westerlies that lock out very cold Arctic (or Antarctic) airmasses and these warm seas cloudy up frigid Arctic airstreams flowing over them minimising surface radiative heat loss, all this in turn helps to keep sea-surface temperatures from dropping, though a month of 100 Watt per square metre cooling of a 400 metre deep layer of ocean leads to just 0.13C of cooling (below 400 metres almost all deep water in high latitudes is near or slightly below 4C) ! So, cold-air advection be needed too, and it would need to be persistent, with winds pushing back any warm ocean-currents from lower latitudes so the ocean cools over a season for a significant impact such that further cold incursions are encouraged (with higher pressure to the poleward encouraged) and are severe and without blanketing cloudy convection preventing night-time radiative cooling over affected mid-latitude islands. And, of course, the entire process can be undone- and more- by the Summer Sun, with clear skies (and high-pressure) more likely over cooler seas. Ocean surfaces have a low albedo when the Sun is high. Thus, unless something major climatic happens (like a quiet Sun with a Grand Solar Minima, or a massive volcano reducing Solar input into the oceans), it means that under current climatic conditions with rising CO2 levels higher mid-latitude oceans will stay well above freezing. This means that middle-latitude islands will continue to be protected from fierce Arctic (or Antarctic) cold in the coming winters- that is unless some pretty extreme set of high-latitude blocking weather-patterns occurs and persists over two or three winters overcoming the ability of the Summer Sun to warm the oceans!

The National Snow and Ice Data Centre so sea-ice limits close to normal positions for mid-October just east of Greenland and in the north of the Davis Strait- even though the Davis Strait remains ice-free. With the Greenland ice-cap also cooling rapidly along with NE Canada, would not the warmer-than-normal surface of the North Atlantic would support stronger baroclinicity in the far North Atlantic going forwards? NSIDC map here:

Continued Once the cold Arctic (or Antarctic) airmass reaches the island mid-latitude region it is likely to be infused with considerable cloud-cover, with cloud of considerable depth about 2 km above the surface. This cloud-cover, in winter, ameliorates the very cold conditions likely to be experienced at the surface because cloud-cover acts as a blanket, greatly reducing night-time radiative heat loss. This means that air-temperatures seldom drop more than a few degrees below the generl temperature of the cold airmass a few hundred metres above the surface. Even if the cold-air advection from high latitudes is accompanied by high-pressure moving in and subsidence up to 500 metres a day, with moisture entering the air from the warm sea-surface at a rate of 1 cm a day (especially likely if the cold airstream is accompanied by strong wind), the replacement of the lowest 2 to 3 km of the atmosphere with dry air at a rate of 20% a day is hardly likely to ensure the cloud-cover disperses. Thus, only very strong subsidence (with some warming of the upper-air to bring the inversion nearer the ground) will bring the clear skies needed for radiation cooling at the surface- a situation that must involve amelioration of the cold temperature of the air some 2 km above the surface so that the airmass is alittle less cold anyway. So, in this second way, warm seas protect mid-latitude islands from fierce high-latitude cold. The third significant manner in which warm seas in higher latitudes protect mid-latitude islands from great cold is by modifying surface atmospheric-pressure polewards of the locations to be affected in a manner that makes those very cold Arctic (or Antarctic) outbreaks less likely in the first place. Upper-air (above 3,000 metres) is invariably extremely cold polwards of 50N (or 50S) in winter, partly as a consequence of Westerly Atmospheric Angular Momentum (created by easterly Trade Winds' interaction with the surface in the tropics and sub-tropics) leading to strong Westerlies- and a resultant limitation in the penetration polewards of warmer air- aloft. Very cold air aloft and warmer air below (as it invariably is over warm sea-surfaces) results in rather lower atmospheric-pressure near the surface. This entire process limits the potential of high-pressure to form and persist poleward of the middle-latitude islands where it could direct frigid high-latitude air towards them. Of course, with sea-surface temperatures in higher latitudes warmer as a result of global warming, this rather limits the scope for frigid high-latitude airstreams to even reach the UK, or to reach Ireland or New Zealand. Warmer seas also limit the scope for these very cold airstreams to then bring clear night skies and extremely low temperatures in winter.

Dear fellow Weather Observers In middle latidude islands and some continental areas in various parts of the World hundreds of miles of warm seas with average temperatures well above 0C in the coldest months separate the region from any source regions from which extremely cold airmasses (with a mean temperature well below 0C at sea-level) may originate. Such areas of the World include the UK, but also Ireland, various Mediterranean islands, southern Japan, Bermuda, New Zealand and Tasmania. Also included are southern Argentina/ Chile as well as southern Australia and South Africa because the continents to which they are attached are only large in latitudes too low to support serious continental cooling and so Antarctica is the only real source region for frigid air- meaning advection across the Southern Ocean is required for this air to reach these continental localtions- so for the purposes of the dynamics of very cold airstreams the southern tips of the Southern Hemisphere continents are included. Quite apart from the modifying influence of much warmer sea-surfaces in warming very cold airmasses passing over them: An airmass of 3 km depth in the lower atmosphere is warmed by roughly 10C in 24 hours if the temperature differential between it and the ocean surface is 20C to begin with because a temperatre differential of 15C leads to a 300 Watts per square metre net heating of the air by the warmer ocean (and the warming will be more than that to begin with), thouh in winter this is offset (to a rather smaller extent) by net radiative heating of the lower atmosphere. In addition, there will be a significant amount of heat (latent heat of condensation) as the water vapour pressure from the warm sea surface greatly exceeds that from the cold atmosphere above- with the result that moisture enters the atmosphere and vigorous convection soon results in cumulonimbus and showers of rain or snow. Thus, you end up with a situation whereby an airmass that starts off at -10C and spends 24 hours over a sea-surface of +10C is likely to be about 2C in the lowest layers after 24 hours. This is why a frigid Siberian airmass, crossing Scandinavia at a temperature of -20C in the lowest layers in winter, is hardly ever likely to be below -5C at sea-level by the time it reaches the coast of eastern Scotland and North East England after its passage across the northern North Sea, the surface of which in January is typically about 8C. But this obvious warming is not the only way warm, ice-free high-latitude seas protect middle-latitude regions from the fiercest onslaughts of Arctic, Siberian or Antarcic cold: It is very clear that the vapour-pressure of warm sea-surfaces compared to a very cold airmass over-running it pumps large amounts of moisture into the air. A strong dry and icy wind at -10C over a sea-surface of 10C can extract over 1cm of water-equivalent, which is more than sufficient to result in deep cloud-cover in an airmass at (say) -5C in the lowest layers and -30C at 3,000 metres (the air would warm more near the surface though less quickly aloft and that would encourage strong convection currents in the still-frigid air). Much of the moisture would freeze out in cloudy convection resulting in sharp snow-showers, which are a feature of very cold airsreams over warm seas, but not all of it. With the moisture chiefly freezing out at higher levels the higher-level air (at 2 to 3 km) warms quite rapidly so after 24 hours this reduces the atmospheric temperature gradient to the extent that convection then proceeds at a lower rate. However, cloud-cover at 2-3 km would act as a stronger surface from which radiative heat-loss maintains the middle-level air at a low-enough temperature to ensure convection continues. Continued below

Hi, been rather busy so not been on here recently. My money is on a slightly milder-than-normal winter in 2022-2023 after a mild blustery autumn overall. Global warming meaning temperatures over a wide area are over 0.5C above long-term normal, Westerly QBO high over the Equator returning just in time to influence winter circulation. Sea-surface temperature anomalies in the North Atlantic of +2C as I speak combined with pack-ice nearer normal around and nw of Greenland indicate greater baroclinicity over North Atlantic (with deeper depressions). Strong La Nina in tropical Pacific that would otherwise lead to less energy entering the Northern Hemisphere circulation (and which would increase the change of blocking/ cold spells) outweighed by the other factors, though a few short cold snaps (from the north/NW) still likely. Ian Pennell

@Roger J Smith The idea of pumping sea-water onto Canadian glaciers in winter- so that the water freezes and increases the surface mass balance- and (hopefully) reduces sea-levels- and also building new glaciers in this way that reflect away the Sun's heat in order to keep the Earth cool are certainly achievable- with sufficient resources and enough pumps. Northern Canada does have large freshwater lakes which can be used in stead of sea-water as the melting point is higher (as is the albedo of pure ice). I agree with the point about the quiet Sun for the next 30 years having a cooling influence that counterracts the effect of rising sea-levels, so it might not be essential to resort to such drastic measures to prevent major tipping points arising until such times. Damming the Bering Straight is certainly doable- a large floating barrier would stop warm currents from the Pacific melting the Arctic ice. Building a real barrier- a wall would require much more in the way of resources, and would certainly stretch the technical capabilities that man possesses today. In the meantime, it is encouraging that COP 26 has produced more agreement from more countries- including India- on the need to reduce CO2 emissions rapidly. Unfortunately, places like Britain- on the west sides of continents in higher middle latitudes- are already suffering from the effects of storms, coastal erosion and greater flooding, some kind of north-south barrier in the North Atlantic or, if more practical, building a massive wind-farm in the North Atlantic west of Scotland both to generate more renewable energy and to slow down the strong winter south-westerlies ought to be considered in the next decade or so to protect our coastal communities and stop them falling into the North Atlantic. An alternative measure might be to invest ££ billions more into strengthening coastal defences and dredging rivers to cope with the storms that will come because of the global warming we already have. Mediterranean lands and countries like Israel already suffer from excessive droughts more than they used to- helping them with water desalination and more reservoirs would be enormously appreciated by these countries. If other readers of this forum have other ideas for Geo-engineering that are practically possible and leave minimal side- effects in terms of pollution, please feel free to share them.

@knocker As the upper warming over the tropics with modest global warming would appear to be the more dominant influence this does tie in with IPCC predictions that higher latitudes will be warmer and wetter in winter with more intense storms as a result of global warming. The reduction in the frequency of prolonged high-latitude blocking bringing bitterly cold northerlies and easterlies for long periods in the UK in winter in recent years does bear this out. The earlier global warming of the 1920's and 1930's was accompanied with few severe winters (1928-29 excepted), and more frequent strong westerlies and heavy rains; the 0.5C global cooling from 1940 to 1970 brought about more frequent blocking and some noteworthy severe winters to the UK, of which 1946-47 and 1962-63 were the most extreme manifestations. For more recent decades, with the exception of December 2010, there has not been a CET with a mean temperature below 0C since January 1987. In the 1980's both February 1986 and January 1987 had a mean CET below 0C- and December 1981 was within three-tenths of a degree of being another month with a mean CET below 0C, as was January 1985. Severe night frosts in April and October were not unknown in the 1980's, but have been virtualy unknown in lowland England in the last eighteen years. All of which suggests that, at least during the winter half-year, high-latitude blocking has been decreasing as the North has got warmer. Other factors help explain why the Circumpolar Vortex and storms should become stronger in winter as the Northern Hemisphere warms- in spite of the Arctic warming faster. One is that a warmer North Atlantic and warmer North Pacific can furnish more moisture (and more latent heat energy to power stronger storms) in a warmer world. The other is to do with the mean latitude of the Westerlies shifting polewards (following the retreating edge of Arctic ice-cover and attendant zones of strong baroclinicity), as the Westerlies shift polewards they have to blow harder to act as a sink for Westerly Atmospheric Angular Momentum put into the atmosphere in the tropics by surface tropical easterlies, that is because the Westerlies blow closer to the axis of the Earth's rotation. A warmer World also means hotter air containing more moisture in the zone of hot rising air near the Equator, which would fuel stronger thunder-storm type convection there, this is something that readily becomes apparent during strong El Niños. More vigorously rising air near the Intertropical Convergence Zone supports stronger NE and SE Trade Winds, and stronger Westerlies aloft in an invigorated Hadley Circulation and greater transfer of Westerly AAM to higher latitudes. Stronger convection near the Equator would lead to greater latent heat transfer aloft and a consequent latent-heat induced warming of the upper air over the tropics, consistent with the article referred to above. This is all consistent with greater Westerly AAM transport to higher latitudes, stronger Westerlies reaching the UK and deeper depressions passing to the north: Strong Westerlies at the surface and aloft tend to preclude high-latitude blocking patterns. If, however, the Arctic basin became very much warmer in winter, perhaps as a result of further climatic warming leading to a complete thaw of the pack-ice and then warm southerly winds from the Atlantic associated with frequent depressions helping to prevent the re-freezing of the Arctic Ocean well into the winter blocking patterns could increase rapidly: The the low atmosphere over the Arctic could be over 20C warmer, which would be enough to greatly reduce baroclinic temperature gradients that fuel the North Atlantic (and North Pacific) depressions- leading to a weakening of the Westerlies. The sinks for Westerly AAM would be pushed into lower latitudes (associated with troughs in a weaker Circumpolar Vortex), as well as the Arctic interior becoming a sink for Westerly AAM associated with depressions. Were that to happen, intense blocking highs over northern Europe could become very frequent- with major implications for winter weather in the UK.

Dear Readers This is a thread which, I hope that fellow members of this great forum can discuss practical geo-engineering solutions to fight Global Warming and to arrest some of the egregious regional climatic trends- heatwaves, drought, floods and storms, coastal erosion, etc.,- that have become more apparent in recent years. Whether one believes we are soon to face Apocalypse or that CO2- induced warming will be cancelled out by natural trends in the next thirty years- temperatures globally- and averaged throughout the year- have undoubtedly risen byjust over 1C since the end of the 19th Century: More severe droughts and wild-fires in the sub-tropics and Mediterranean latitudes and more devastating floods and storms in higher latitudes certainly have the potential to not only destroy habitats but also cause great economic hardship, destroy homes and offices and displace significant numbers of people. And, at this time, with China and Russia staying away it looks like COP26 will end up being little more than a jolly of G20 World leaders: If China, Russia and (likely) India will not countenance really cutting down coal production and burning (these are by far the biggest CO2 polluters), what hope is there for curbing CO2 increases to stop global mean temperatures getting above the 1.5C threshold whereby unstoppable feedbacks set in causing sea-levels to rise precipitously? In the light of all this, and the huge economically-damaging costs of Net Zero, forcing people to go electric by a certain date, putting higher costs and taxes on businesses and home-owners in Britain (and potentially bankrupting the country), I think the Government could abolish the Climate change Act (2008) and strike down the legal commitments to make Britain carbon-neutral by 2050 (costs of this in excess of £1 Trillion are conservative estimates). If the Chinese and Indians are not going to bankrupt their economies to persue Net Zero, then why should Britain when it is not going to have much effect? A different approach is needed. Firstly, Britain should incentivise business and companies to go green using tax breaks. There are still over £20 billion of stakes in part-nationalised banks still on the Government's books, these could be sold and the proceeds used to cut taxes on green products- economic growth and the revenues from the increased "Green Economy" will help make these tax breaks self financing. Secondly, rising CO2 levels, Global Warming and some of the unpleasant side effects (like increased drought in the Med and coastal erosion from more winter storms in high latitudes) need completely different, new approaches to tackle them. Again, R & D funds can be directed at the scientific community to develop real solutions to Global Warming, funded more by (perhaps) cutting the size of Quangoes. And talking of real solutions, please feel free to discuss practical, but effective solutions to reducing global temperatures- and dealing with some of the now- apparent unpleasant side-effects of a warmer World. Some ideas I have seen around, that could be economically feasible and practical (but with limited side effects) are as follows. These might need a Coalition of the Willing countries to just do (getting full Global Agreement for anything these days seems to be nigh-on impossible!): 1) Spraying sea-water into the troposphere over tropical oceans (with pumps from the sea-surface supported by large balloons (hot air balloons or filled with helium, whichever is most practical). The fine salt solutions sprayed into the atmosphere leads to moisture and condensation nuclei causing the ready development of more cloud. The increased cloud over tropical oceans would reflect more heat from the Sun back to space and help keep the Earth cool. The costs of a few thousand large balloons and pumps- and some helium should not be more than a few £ billions. 2) A fleet of suitably-modified high-flying jets could spray milions of tonnes of suplhur dioxide into the stratosphere around the Equator- above the altitude where it will be rained onto the surface from rain and high-altitude snowfall. Half a metre thickness of sulphur-dioxide above 20 km would have a dramatic effect in shielding the Earth from the Sun's rays whilst the settling of this sulphur dioxide is likely to be sufficiently gradual as to cause minimal damage to ecosystems, the environment and communities at the Earth's surface. Relatively cheap and practical to do, but likely to be great resistance from Environmentalists. 3) Salt extracted from sea-water. Billions of tonnes of powdered salt could be carried up to the edge of Space by thousands of specially- constructed Earth- orbiting rockets. These rockets would fly west-to-east around the Equator (and other low latitudes) releasing the powdered Salt- which would remain in orbit around the Earth- a man-made Earth ring (like Saturn's). The Earth-ring of powdered salt rotating around Earth at the edge of space would reflect the Sun's rays back into space and help keep the Earth cooler. At a cost of a few ££ billions, this could buy time for global markets to work on CO2-neutral energy and transport solutions. 4) Pump large amounts of purified sea-water (or fresh water from glacial rivers/ lakes) using giant pumps and large pipes to the top of the Antarctic Pleateau and the top of the Greenland Ice Cap (in their respective autumns and winters) where it would freeze in the very low temperatures. The release of latent heat as vast quantities of water freeze would reduce the atmospheric temperature and pressure gradients (that is what meteorologists call the atmospheric baroclinicity) that drive powerful storms at higher mid-latitudes- helping to stem some of the heavy rain, flooding and coastal erosion in places like Britain, western Norway and western Canada. The freezing of water onto the ice sheets would help build up the ice-sheets and (in the process) help to reduce sea-level rises. This process could be taken further by spraying and freezing water onto large parts of northern Canada (with their permission) in the winter, over a designated a new ice-sheet. If ten metres' thickness of ice can be built up over a large part of Northwest Territories the ice would not melt away the following summer and the new ice-sheet would reflect away the Sun's heat. Thereafter the new ice-sheet could be built up the following winter by being hosed from some of Canada's many tundra lakes- the water would freeze and build up the ice-sheet and the release of latent heat would weaken the baroclinicity downstream- meaning less damaging winter storms heading towards Britain. This is practical, the costs are likely to be just a few £ billion (which rather compares favourably with over £1 Trillion for Net Zero!). 5) Cause a mild "Nuclear Winter" (or "H-Bomb Winter") to fight Global Warming by dropping a couple of powerful H-bombs on an evacuated desert island. Hydrogen bombs dont cause nuclear fall-out but (if powerful) they could send enough dust and ash into the Stratosphere to reflect heat from the Sun to but more time as the World moves towards CO2-free energy and transport solutions. A variation of this might be to try and bomb a normally- explosive volcano in a remote area to provoke it into exploding and releasing vast amounts of dust into the Stratosphere. This is probably the cheapest option, but would be very much a last resort! As this is intended to be a thread to discuss Geo-engineering solutions you are welcome to propose your own, different, ideas. If you think the above are non-starters what do you think might work? Should Western Nations bankrupt their respective economies and impoverish their populations for a vain cause (which it will be if China and India keep belching out CO2 and refuse to reduce emissions)? Ian Pennell

@ ANYWEATHER A wall up to 4,000 metres (just over 13,000 feet) built north to south from 60N to 35N- just off the Canada and USA coast would be a challenge but, I don't think, completely impossible if there was the will to do it. The seas around Britain are already prolifering with wind-farms galore and- in the past- large oil rigs were constructed and put into position in the North Sea. Huge concerete blocks could be manufactured elsewhere and moved into position with the help of some large ships and a few cranes- and moved into place with the assistance of underwater cameras. It would be just offshore- so still on the continental shelf where the sea depth is no more than 150 metres. The wall would need to be 500 metres thick to withstand the forces it would be subjected to, particularly waves and strong winds. And at 4,000 metres' elevation the wall will be consistently exposed to strong 100 mph Westerly winds between October and April - associated with the Circumpolar Vortex- hence the reason for building it: The plan would be to construct a major sink for Westerly AAM- so that the Westerly AAM does not bring strong Westerlies and damaging storms downstream- i.e., over northern Europe, to stop storms that often bring warmth to the Arctic interior too where thy accelerate the loss of that all- important high-albedo ice-cover. Certainly, the floating mirrors on the equatorial Pacific and Atlantic would be a far more feasible option for achieving the same result: Weaker North East and South East Trade winds feeding into a weaker zone of hot rising air near the Equator and- as a by- product- weaker Westerlies and less "Warm sector conveyer belts" bringing ice- destoying heat to the Arctic (and coastal Antarctic). If giant wind-farms can be constructed at sea, large floating mirrors with a single anchor to the sea-bed are certainly doable. Bit this is a point to consider: If NO Geoengineering schemes are EVER to be considered then the World is left entirely at the mercy of China, Russia and India- where rapidly-growing populations and pro-growth governments will not voluntarily impose measures that impose hardship on their populations in order to reduce CO2 emissions (look who is not going to be at Cop 26!). Should Britain and other Western countries impose Net Zero and other economically- harmful Green policies whilst China and Russia laugh at us? There is nothing that Britain can do to prevent significant further Global Warming without their cooperation, and really a proper Conservative Government would (sensibly, in my view) tear up the Climate Change Act (2008) and Net Zero legislation in view of this, especially as Britain is on the verge of Stagflation! Yet Global Warming is real, even if it is not as great as some of the Environmentlists and the IPCC might suppose with rising CO2 levels. Britain's coastlines are precious, coastal communities deserve effective measures to protect them (and I don't mean ever-greater sums spent on coastal defences in the face of winter storms and floods that could smash these like match-sticks). Bugs and pests are spreading and- unkilled by winter frosts- will lead to ever more disease and pestilence. Farmers suffer increasingly from bugs and pests blighting their crops in warm, damp autumns (I have a nice crop of Brussels sprouts at home, but all full of weavils!!). And carbon capture and planting millions of trees is not going to be enough to arrest this change without 100% Global Co-operation (which is about as likely as the Sun going out tomorrow).

The huge expense in trying to combat Global Warmng- through taxes on Carbon, Net Zero- thus helping to stop the higher-latitude Westerlies "Getting out of hand" and causing irreparable coastal erosion in Britain and other parts of northern Europe- is likely to be in vain if we cannot get China and india to curb their CO2 emissions. But at a fraction of the cost, Britain and other countries working together might find another means of taming (and perhaps even reversing) Global Warming by implementing geo-engineering measures that weaken the Westerlies, reduce the number and intensity of strong "warm-front conveyers" associated with depressions that push a little too much heat and wind into high latitudes! If we can reduce the number and intensity of depressions and strong south-west (and southerly) winds moving into the Arctic basin you help preserve the ice there (it may hopefully recover) and that ice then reflects heat from the Sun as it persists through the summer- keeping the Earth cooler. Some measures to do this include the following: 1) Building a 4,000 metre-high wall (500 metres thick); running north to south from northern Quebec to Atlanta (it can be built just off-shore to avoid it going over valuable farmland and communities). This would be a huge undertaking costing $$100 billions but it would be cheaper than all the huge efforts to combat Global Warming running into $$ Trillions. A 4 km-high wall would be effective at intercepting the Westerlies where they are stronger- the force of the wind against this high wall would be a very effective sink for Westerly AAM- leading to weaker Westerlies downstream. The high wall would also create an upper trough (with depressions and associated Westerlies blowing further south) downstream, bringing rain to the parched Mediterranean and Israel whilst relieving Britain of damaging storms and coastal erosion (and brining about colder, drier winters in Britain, too). The Arctic would get a chance to cool, as would Siberia. That will preserve reflective ice-cover and prevent the Siberian permafrost thawing (and all that entails). 2) A cheaper, more practically feasible option (one that will require International Agreement) is to cover 2 million square miles of the Equatorial Atlantic and Pacific with floating mirrors- perhaps attached to the sea-bed by long chains so that they can't drift over fishing lanes, shipping areas or troucle coastal island communities. The mirrors would reflect away the Sun's heat (helping to keep the Earth cool) and the cooling of Equatorial waters would help weaken the zone of hot-rising air in the deep tropics. This would, in turn, weaken the converging North East and South East Trade Winds, reduce the addition of Westerly AAM to the global circulation and, thus, weaken the Westerly AAM available to furnish depressions and Westerlies in higher latitudes. Weaker Westerlies and depressions in the North means less "warm front conveyer belts", less Winter storminess and the Arctic being allowed to cool. That in turn means more reflective ice there (and also around Antarctica), which could be enormously effective at countering the greenhouse effects of rising CO2 levels. The Med and Israel will get much-needed rain, Britain and northern Europe will benefit from hard winter frosts to kill the bugs and from less coastal erosion. There will also be more decent summers in northern Europe. However, as far as Climate Change is going, the Clock is Ticking and there is perhaps just forty years to prevent serious Global Warming and all that entails! At the moment a Quiet Sun is helping, by counterring the CO2 warming effect, in forty years time the strong Solar Sunspot Cycles will be back and the Sun will amplify Global Warming. It does not look like we can rely on China.

So, almost all year round in both the Northern and Southern Hemispheres, there are no strong Westerlies over an extensive area between 36.9 degrees South and 36.9 degrees North, at leas not that impact the Earth's surface. This has been the case fairly consistently over the last decade. It means that Westerly AAM is generated over half the planet- in low latitudes where the Easterlies are most effective at adding Westerly AAM to the atmosphere by surface friction (or by easterlies blowing against mountains causing a mountain torque) as they blow far from the axis of Earth's rotation (think of sitting away from the centre of a see-saw). The surface Westerlies, which act as a sink for Westerly AAM all blow appreciably closer to the axis of Earth's rotation given they are restricted to the 40% most poleward sea and land surfaces of the Earth- and therefore they have to blow extra hard! This explains why the Westerlies have to blow stronger and more consistently in the North. And the warmer seas and oceans and retreated margins of Arctic ice help furnish stronger depressions that move in higher latitudes- and that, too, is consistent with the stronger Westerlies that blight our recent winters with so much rain, wind and mildness for those who like "Proper Winters". Hotter, steamier conditions near the Equator add fuel to the rising air and thunderstorms that dominate the low- pressure areas there. That is expected with rising CO2 levels. Faster rising air near the Equator helps strengthen the North-East and South-East Trade Winds that converge on it- and hotter summers in whichever tropical areas are getting summer strengthens the Equatorial Easterly Jet-stream (about 5,000 metres above sea-level and able to blow against Kilimanjaro, the northern Andes and the mountains of Papua New Guinea). That, in turn means stronger sources of Westerly AAM extensively across the Tropics and sub-tropics- and a need for more persistent and strong Westerlies in higher Northern and Southern latitudes. And the strong Westerlies in higher latitudes of the Southern Hemisphere, both at the surface and aloft explain the unusual extreme cold over interior Antarctica and the re-emergence of the Ozone Hole: These strong Westerlies, associated with deep depressions that encircle Antarctica (some below 930 millibars at the centre) form a barrier stopping frigid air leaking out towards Argentina, South Africa or Australia but they keep the frigid air over Antarctica pure- with little warmer air from lower latitudes getting through. The very frigid air continues to cool in the sunless winter over interior Antarctica (where skies are often clear and maximising heat-loss from the ice surfaces)- and so the extremely low winter temperatures (even lower than normal) at the South Pole are explained. Aloft, the tight vortex of circumpolar Westerlies intensifies during the Antarctic winter (helped by conditions below) and- in the absence of any sunlight- the Stratosphere over interior Antarctica gets intensely cold, that is, below -78C. This is cold enough for minute ice-crystals to form- which facilitate chemical reactions that destroy ozone in the presence of minute amounts of other pollutants (chlorine- based)- these happen when the Sun returns to the interior Antarctic stratosphere (August- September). With strong Stratospheric Westerlies encircling Antarctica ozone-rich upper air from lower latitudes cannot penetrate: Thus you have an Ozone Hole. This concentration of the Westerlies in higher latitudes and mainly just Easterlies in the Tropics and sub-tropics, both in the Northern Hemisphere and Southern Hemisphere is associated with persistent high-pressure near 35 degrees North and 35 degrees South. So whilst Israel and California suffer droughts and summer heatwave, Britain has (mainly) wet mild autumns and winters and frequent flooding and storms, warm airmasses penetrate as far as Siberia even in winter and bring thaws (unheard of in the 1980's) but Antarctica suffers very extreme winter cold (average winter temperature in 2021 at the South Pole was -63C) and an Ozone Hole. Strong south-west winds from the Atlantic have penetrated right up towards the North Pole on occasion- raising the potential for complete ice-loss.

Dear Readers, Rising CO2 levels in the atmosphere has undeniably had a warming impact on the Earth's climate, with the planet as a whole having a mean temperature during 2020 just over 1.0C above pre-industrial averages. The warming impact has undeniably been greater in recent years in Russia, Canada, and northern Europe where- in the winter months the mean warming has been over 2.0C above pre-industrial averages for the season. Some of this warming may be related to the Earth coming out of the Little Ice Age- but some of the effect is undoubtedly due to CO2 levels since we are entering a period of quiet Sun (weaker sunspot cycles with slightly weaker Solar output) which, all else being equal ought to bring a cooling back to the conditions of the 19th Century: Plainly that is not the case. But why do middle latitudes and higher latitudes in winter warm more? The exception is interior Antarctica that has got colder in recent winters, and winter 2021 (June-August) was one of the coldest on record at the South Pole. The Antarctic Ozone Hole in the Antarctic stratosphere has also made a bit of a come-back in 2021 (during the Southern winter). Is that also in some way related to warmer, wetter winters in most middle and high latitude areas? The answer is a definitive "Yes". Most meteorologists appreciate the impact of something called the Law of Conservation of Angular Momentum on the Earth's global weather-pattern: In layman's terms, the Earth's rotation and the virtual absence of outside forces (gravitational tidal influences from the Sun and Moon, the effects of meteorites and bursts of super-charged plasma from the Sun following coronal mass ejections are largely negligible over just a few years) means that the atmosphere as a whole has to rotate with the Earth. From this, the frictional and pressure impacts of Easterlies at low latitudes and near the poles are counterbalanced by the frictional and pressure impacts of Westerlies in middle latitudes. This applies to both the Northern Hemisphere and the Southern Hemisphere and largely dictate the existence of the Westerlies in higher latitudes, but not necessarily where they occur or how strong they are. However, global weather- patterns are also (and primarily) controlled by the heat input to the Earth-Atmosphere system, how much heat there is and where it is on the Earth. It is also dependent on moisture and atmospheric temperature gradients. A warmer Earth not only means more moisture in the atmosphere but, with the edges of polar ice-caps (seasonal and year-round) retreated polewards it means that the Westerlies- intensified and largely fixed by atmospheric and near- surface temperature gradients (what meteorologists call baroclinicity) as the depressions that drive these depressions also need these zones of baroclinicity. Now, the areas of the Earth where easterlies are at the surface are called sources of Westerly Atmospheric Angular Momentum (AAM) or simply Global Atmospheric Angular Momentum (GLAAM). This arises because Easterly winds, blowing in a direction opposite to the Earth's rotation result in the Earth losing a bit of it's eastwards rotation to the atmosphere- in other words these areas with surface Easterly winds are sources of Westerly AAM (or GLAAM). Since, at least under current climatic conditions, the winds aloft do not start blowing 1,000's of miles an hour from the West and remain fairly constant in speed at the height of the winter (seldom more than 200 mph at 10,000 metres' elevation) it follows that other areas are sinks for Westerly AAM (or GLAAM). These areas are in higher latitudes where often -strong Westerly winds blowing over the sea or against hills result in a frictional force at the surface slowing the Westerlies down- and helping to speed the Earth's rotation up. The fact that the Length of Day remains fairly constant throughout the year- and from year to year (though the Length of Day is very slowly increasing by a millisecond a decade mainly due to the effects of marine tidal friction due to the Moon)- means that Westerly AAM is imparted to the rotating Earth as much as it is removed via tropical and Polar Easterlies. Now, for some interesting observations of global weather maps by a seasoned meteorologist (myself): For almost all the year the Westerlies seem to be concentrated at the highest latitude 40% of the Earth's surface (sin-1(1-0.4)=36.9 degrees, so that is Westerlies restricted to North of 36.9 degrees North and South of 36.9 degrees South). Of course, there still are some occasions with Westerlies in lower latitudes, strong Westerlies occur on the equatorwide of hurricanes and tropical depressions when these occur but these are counterbalanced by just as strong violent easterlies on the other side of these tropical storms. South-Westerlies blow over India and adjacent parts of southern Asia during the Summer Monsoon- which will help reduce some of the need for strong Westerlies at higher latitudes of the Southern Hemisphere in the winter there, so this will not help weaken Westerlies in high Northern latitudes. Often the Tibetan Plateau gets Westerly winds in winter, but these have seldom been strong and they are restricted to those areas north of 30 degrees North. (Continued below)

Continued. Whilst a World without convection is out of the question, mainly because the surface and lower atmosphere have a net heat surplus of about 50 Watts per square metre whilst the upper atmosphere loses heat at a rate of 50 Watts per square metre (averaged globally throughout the year), one cannot underplay the importance of deep atmosphere convection in bringing clouds and rainfall across the World. Even in higher latitudes in winter, the deep depressions that bring rain and snow depend (to a considerable degree) on convection to remain healthy. Oceans at higher latitudes cool only gradually with the season whilst prevailing westerly winds keep the western continental margins furnished with surface air that is just above freezing- point. Aloft, the air is extremely cold (-60C at 10,000 metres above the surface). The air temperature drop with height is thus just over 6C per 1,000 metres' elevation and moist air rising in a depression- and condensing it's moisture content as it goes- cools at a rate of almost exactly 6C per 1,000 metres- as the moisture condensed and frozen out gives up a lot of latent heat in the process of freezing out. Thus the air stays marginally warmer than the air around it as it rises, causing the air to rise faster because being a little warmer it is lighter. So the air rises faster and provides energy and impetus to the depression. If our Winter depression then moves into Russia and entrains air that is below -10C at sea- level, then with the air at 10,000 metres still at -60C the lapse rate drops to 5C per 1,000 metres. Rising air in the depression still cools at 6C per 1,000 metres- and in rising higher becomes colder (and relatively denser) than the atmosphere around it. Thus convection stops, the colder air in the low elevations of the depression can no longer rise effectively- and our Winter depression quickly fills. This is why depressions penetrating the Central Arctic in February quickly run out of steam and fill and why deep depressions are normal in the Southern Ocean around Antarctica but you rarely, if ever, get a deep depression over the South Pole in any season. Even in the deep tropics, areas of cooler sea- surface temperatures or warmer than normal conditions in the high atmosphere can sharply weaken convection and the rain- bearing thunder-storms that depend on it. The Intertropical Convergence Zone (ITCZ), where hot steamy air in low latitudes rises and fuels spectacular thunderstorms, is largely driven not by converging Trade Winds from the Northern and Southern Hemisphere but by the vigorous up-draughts of a myriad of thunderstorms which pump large amounts of latent heat into the upper atmosphere causing atmospheric divergence aloft and a fall in surface- pressure below. It is the powerful convection currents of thousands of thunderstorms that fuels the ITCZ and that, in turn draws in the Trade Winds below- sending Westerly Atmospheric Angular Momentum (AAM) through the frictional interaction of the easterly Trade Winds with the underlying surface. And that Westerly AAM, under current climatic conditions also helps to fuel depressions in higher latitudes with the attendant surface Westerlies acting as a sink for Westerly AAM. Without the cloudy thunder-storm convection of a myriad thunderstorms along the ITCZ the entire house of cards of the global weather- machine would collapse. If the surface of the lands and oceans near the Equator were 5C colder than nowadays, but the upper-air is the same temperature almost all of the convection driving the ITCZ would collapse because the temperature drop with height would be such that rising parcels of air would become cooler than the surrounding air before much moisture could condense out. Relatively dry air at temperatures typical of the low atmosphere in the tropics cools at a rate of 10C per 1,000 metres, so convection would quickly run out of steam before condensation (and latent heat release) of warm moisture- carrying air reduces the effective lapse rate to 5C per 1,000 metres (which is what fuels deep thunder-storm convection). So an Equatorial zone just a few degrees cooler than today at the surface would scarcely maintain an ITCZ, the Trade Winds converging from north and south of the Equator would be very weak and, without the transfer of Westerly AAM into the global atmospheric circulation there would be very little Westerly AAM transferred to higher latitudes- for which read, means no Circumpolar Vortex, no extra-tropical depressions and no Westerlies in higher latitudes. And that would be all for the want of vigorous thundery convection in the deep tropics! The effectiveness in cooler- than- usual surface conditions in killing convection (and thus rainfall) in the tropics can be seen from low rainfall amounts on the coast of Ecuador and Peru- where the cool Humboldt current effectively kills convection and leads to semi desert conditions just inland.

Dear Readers Underpinning depressions (particularly the tropical variety), tall cumulonimbus clouds bringing heavy showers and thunderstorms and even widespread heavy rainfall or snowfalls occurring over hills in high latitudes have one vital ingredient for their occurrence: Convection. Atmospheric convection lies at the root of strongly rising air (or even gently- rising air originating over an ocean surface or moist land) that brings about cloud- formation and rainfall. If the surface of the land were much colder, the oceans frozen and/ or the upper troposphere a good deal warmer convection could not occur- anywhere, even in areas where the atmosphere rises because of convergence into the region (and rising air in the hot, steamy tropics and in the vicinity of deep mid-latitude depressions largely depends upon convection and the release of latent heat in the rising cooling air to fuel up-draughts). The situation with an atmosphere without convection means that the areas of rising air would invariably cool faster than the surrounding air- and become denser in the process: Thus the convection currents would be still-born (and probably before the moisture contained in the rising air- parcels cool to the point where the moisture condenses out). The Earth's Hydrologic Cycle would be much weaker, and it would be largely restricted to the oceans- because rainfall over land requires moist air to be pulled inland by areas of vigorously- rising air associated with depressions (and, of which, convection, condensation and the release of latent heat as moisture condenses in rising air is a major part). If the oceans were frozen, very little evaporation could happen in any case but- without mixing with air above it, the atmosphere in a fairly shallow layer over the surface (no more than 500 metres with strong winds, below 50 metres with light winds) would soon reach saturation during periods of nocturnal cooling leading to widespread dense fog (or freezing fog) out of which fine water droplets or ice-crystals would fall back to the surface. This process would balance the net evaporation rate from a frozen/ cold ocean surface. If convection cannot occur and rising air gets colder than the air around it (and no warmer than air up to 500 metres above it), that shallow layer of moist air is not going to go very far and even mixing with the air above is greatly limited by the air not been warmer than that above it- in the same way that today any rising moist air in the upper troposphere mixes very little with air higher up in the Stratosphere because of the very temperature profile of the atmosphere there. It follows, therefore that the only moist layers of air would be shallow layers of air over the oceans if there could be no atmospheric convection on Earth: These shallow layers of air over the oceans would be at or very close to saturation all the time- with the result being that the world's oceans would be largely shrouded in fog- particularly at higher latitudes and over parts of the oceans in low latitudes that had come through a night of radiative cooling. With so much of the watery 70% of planet Earth shrouded in sunlight- reflecting fog the planetary albedo would be well above 40% resulting in sharply lower global temperatures (with the oceans freezing at higher latitudes). Over the continents the lack of moisture and rainfall would quickly turn vast areas into desert: And bright deserts reflect more heat than dark vegetated land-surfaces and the very dry atmosphere above would assist in bringing about greater radiative heat loss- all of which would help keep the Earth even colder. Continued below.

Continued. This Ekman Spiral effect beneath the subtropical jet-stream is only effective in creating the Ferrel Cell (with surface Westerlies in middle latitudes) when four conditions are met: Firstly, that subsidence beneath the subtropical jet-stream subsides subsides at the subtropical high fairly slowly- so that it can drag the air beneath it equatorwards before it impinges upon mountain ranges. If it is rapid the strong flow of air from west to east will hit mountains like the Himalayas and South American Andes before it has had a chance to move equatorwards (over areas the Earth rotates faster) and lose its "Westerliness". If the subtropical jet-stream descends fairly quickly it also pushes air eastwards lower down in the atmosphere before it itself moves equatorwards- and the lower altitude air would still have a considerable component from the west (as well as from higher latitudes) on hitting more extensive upland areas. Secondly, the subtropical jet-stream needs to be polewards of 25N and 25S, in latitudes where the Coriolis force is sufficient to cause an effective Ekman Spiral effect. During the coldest winters in the last Ice Age the subtropical jet-stream would have been strong above 25N, where the Coriolis Force is little over two thirds what it is at 35N. A much colder, denser (and shallower) troposphere polewards of 25N, especially over the continents would have also intensified the pressure- gradients at the top of the troposphere further strengthening the subtropical jet-stream but the Coriolis/ Ekman effect on the air beneath with the strong Westerly sub-tropical jet-stream itself not being deflected equator-wards as much. Winds over the subtropics would- thus- have regularly have maintained a strong Westerly component even down to elevations as low as 3,000 metres (and that is with subtropical-high atmospheric subsidence rates similar to today). An equator-wards- positioned subtropical jet-stream would have meant more low- latitude mountains were the sink of Westerly GLAAM. Thirdly, extreme cold over middle and high latitudes during the severest of Ice Age winters would have precluded the mid- latitude Westerly Ferrel Cell over large areas, particularly over the continents in the Northern Hemisphere. The situation would have been analogous to the situation over Asiatic Russia and Mongolia in winter today where intense cold and high-pressure are normal. If the lowest 3,000 metres of the atmosphere were 30C colder than today, but conditions aloft are little colder that increases the density of 30% of the atmosphere by 15%- which equates to a rise in sea- level pressure by 45 millibars- even assuming the Ekman Spiral effect beneath the subtropical jet-stream is trying to reduce surface barometric pressure in higher latitudes as it is today . The sinks for Westerly GLAAM would clearly be displaced from the entire region- upwards and equator-wards. The shallower troposphere over mid- latitudes that would ensue (5 to 6 km depth, not 9 km as nowadays) would enhance the baroclinic temperature and pressure gradients in the upper- air near the subtropical jet-stream, much colder air seeping from higher latitudes near the surface in the subtropics would intensify the subtropical high- pressure belts and precipitate more rapid descent of air in and beneath the subtropical jet-stream (the mountains beneath which would become major sinks of the Westerly AAM unable to make landfall in frigid high-pressure areas in higher latitudes). With no Ferrel Cell aloft over middle latitudes there's no return flow from higher latitudes aloft to slow down the subtropical jet-stream either- the strong Westerly subtropical jet-stream maintains its speed on descent until it hits something else to slow it down (like the Himalayas and Tibet). Finally, during the coldest winters at the height of the last Ice Age the surface and lower atmosphere- with expanded pack-ice, deserts in low latitudes and ice-sheets in middle and high latitudes reflecting away the Sun's energy there would have been reduced temperature contrasts between a chilly surface and frigid Stratosphere. This would have applied almost everywhere on the planet and the result would have been a general decrease in the thickness of the troposphere by up to 1,000 metres compared to today (but a sharper decrease in its thickness in middle latitudes). This the strong sub-tropical Westerly jet-stream would have blown at a lower elevation and would have had less distance to descend before hitting extensive mountain areas. For all these reasons, during severe Ice Age winters in the Northern Hemisphere the transfers of GLAAM and Westerly AAM are radically altered from one where Westerly AAM is transferred from low latitudes and the highest latitudes to middle latitudes- to a budget of GLAAM whereby Westerly AAM is transferred from low-lying lands and seas in all latitudes to high mountain areas in all latitudes (except right on the Equator where weaker Easterlies blow). The change to full Winter Ice age conditions would involve a permanent shift to stronger Westerlies aloft (over the Earth as a whole), more extensive Easterlies below and a slight reduction in the speed of the Earth's rotation (increasing the Length of Day by a few milliseconds). This is not inconsistent with the Law of Conservation of Angular Momentum since there need not be a net change in the axial Angular Momentum of the Earth- Atmosphere system for the above to happen. The existence of the mid- latitude Ferrel Cell- with surface Westerlies angling in from lower latitudes to bring warmth and moisture and returning to the subtropics aloft- is sensitive to a number of factors coming together. Even today, there are times and places in higher latitudes where it is not found at the surface: Asiatic Russia in winter being a good example, as here early winter snowfalls encourage rapid surface cooling and the development of very cold high-pressure areas that displace the Westerlies upwards- and away from that region. This process would get underway earlier in the season and cover a much wider area during an Ice age. The Coriolis effect today acts on the subtropical jet-stream and the air below pulled along by the subtropical jet-stream: With current climatic conditions- with a deep troposphere and slow subsidence beneath the sub-tropical jet-stream and that subtropical jet-stream being far enough from the Equator the Coriolis forces can bring about a return of considerable depth of atmosphere towards the Equator- and helped by ice-free seas and oceans in higher latitudes- results in sharply lower pressure in high latitudes: So the Ekman Spiral effect helps to create the mild moist conditions that bring warmth and moisture to the North, but that happens under current climatic conditions.

NORTHERN HEMISPHERE SEVERE WINTER IN ICE-AGE: RELEVANCE OF THE "EKMAN SPIRAL" AFFECT ON ATMOSPHERIC CIRCULATION A further consideration, with regards to the behaviour of the Global Circulation and Global (Westerly) Atmospheric Angular Momentum (GLAAM) sources and sinks is a feature called the Ekman Spiral, which is related to the Coriolis effect- and which affects related not only surface winds and ocean currents, but it also governs how air that is "dragged" along by faster moving air aloft moves. The Ekman Spiral effect explains why surface atmospheric pressure becomes lower polewards of the subtropical high-pressure belt (in normal climatic conditions). The Ekman Spiral is illustrated here: The above is an illustration of how the Ekman Spiral comes about in the Northern Hemisphere, in this case through the top 100- metre layer of an ocean in mid-latitudes normally affected by strong westerly winds. In Northern latitudes the force of the wind drags the water along in the direction of the wind but the Coriolis force- due to the effect of the Earth's rotation on the water itself acts to the right of motion of the water, causing the surface currents to be 45 degrees to the right. Thus, if the prevailing strong wind is Westerly, the current affected by the wind flows north-west to south-east (and at a lower speed). About 20 metres below the surface the north-westerly surface current drags along the waters below- from northwest to southeast, but the Coriolis Force again acts to the right- so that the flow of deeper water is more of a northerly (at even lower speed). This process repeats until (at 80 metres' depth) below the surface there is a very sluggish flow of water flowing in the opposite direction (from east to west). The tips of the vectors- of the wind- then the currents at the surface and a different depths describes a spiral shape- hence the Ekman Spiral. Much the same process happens high up in the atmosphere beneath the subtropical jet-stream (nowadays typically about 30- 35N and 30- 35S) and some ten kilometres above sea- level initially). The subtropical jet-stream is so high and subsidence beneath it slow enough that the winds 10,000 metres above have little bearing on the winds at the surface. Typically, the strong 150 mph Westerlies of the subtropical jet-stream descend slowly and enters an area where pressure increases polewards- the Westerlies are thus pushed towards the Equator (where the Earth rotates more rapidly) and- in the process- lose their "Westerliness" relative to the underlying surface. The fast moving Westerlies of the subtropical jet-stream also try to drag the underlying air beneath it eastwards, but this underlying air is in the zone without a strong south to north pressure gradient (in the Northern Hemisphere) and it behaves like the surface of the sea under the influence of strong Westerlies: Because of the Coriolis force, this underlying air is pushed to the right (i.e back towards the Equator) as well as from west to east (at a lower speed to the subtropical jet-stream above). The net result of all these processes, under current climatic conditions, is that the subtropical jet-stream causes beneath it- an equatorward push of a substantial layer of the atmosphere in the subtropics. This leads to a situation whereby a considerable "depth of atmosphere" is constantly moved equatorwards of 35N and 35S, which in turn manifests as a sharp fall in surface pressures polewards of these latitudes. With ocean surfaces and lands in middle latitudes just 10C colder than 35N and 35S the dynamic "Ekman Spiral" process easily overcomes the propensity of cooler surfaces in mid- latitudes to help foster even higher surface pressure and the mid-latitude Ferrel Cell (with surface Westerlies) is the result- and the warmer Westerlies originating in somewhat lower latitudes, upon picking up moisture and interacting with cold air aloft (and meeting colder airmasses at high latitudes) further helps fuel higher-latitude depressions that strengthen the Ferrel Cell. But there are clearly some situations where the whole house of cards maintaining the higher- latitude Westerlies falls flat. Continued below.

Continued. A 3C warmer Earth with an ice-free Arctic Ocean year-round has profound implications for the Global Westerly Atmospheric Angular Momentum (GLAAM) fluxes. In the absence of an outside force a rotating mass maintains the same total angular momentum, this is the Law of Conservation of Angular Momentum and for the Earth and its atmosphere this does closely approximate to being true (outside forces such as lunar tides and meteorites are miniscule compared to the exchanges in Westerly Atmospheric Angular Momentum (AAM) between the surface of the Earth and the atmosphere. This means that the total axial Angular Momentum of the Earth, its oceans and atmosphere must remain constant though it does not preclude exchanges between them- or for the atmosphere to rotate faster whilst the Earth and oceans slow down a minute amount. In practice, and under most climatic conditions on Earth that one might care to consider, what this means is that the atmosphere gains Westerly AAM (which makes the atmosphere rotate west to east more compared to the underlying surface) at the same rate that it loses Westerly AAM elsewhere. Under current climatic conditions, the Earth's atmosphere gains Westerly AAM as a result of the frictional impact of tropical and sub-tropical Trade Winds (that tend to blow from the east but also towards the Equator) and tropical easterlies coming up against mountains (mountain torque). The atmosphere loses Westerly AAM where Westerlies blow over the Earth's surface in higher latitudes, although where strong Westerlies impact mountains in mid-latitudes there is also a mountain torque (due to pressure being lower on the lee side of mountains with respect to the wind), which also removes Westerly AAM from the atmosphere. In high latitudes there is usually high surface-pressure over frozen lands and seas and the Polar Easterlies add Westerly AAM to the atmosphere, again through frictional interaction with underlying surfaces (again, this is balanced by the Westerlies in mid-latitudes). However, how Global Warming impacts on the GLAAM fluxes and the sources and sinks of Westerly AAM also has very profound implications for the North Atlantic Westerlies that bring winter warmth and moisture to western Europe: So far as the Northern Hemisphere Circulation is concerned an ice-free Arctic attracting increased storminess means that mean wind- directions will become strongly Westerly over extensive areas of the Arctic, particularly in winter. And unlike mid-latitude depressions a deep depression centred near the North Pole would have its centre north of just about everywhere else in the Arctic Ocean so the depression would bring strong westerly winds everywhere (there would be no "north of the depression" where there are easterlies). Thus, deep Arctic depressions would become significant sinks for Westerly AAM, though the impact of the Westerlies would be muted by the fact that they blow close to the axis of the Earth's rotation. All the same, if the Arctic north of 60N had Westerlies in winter with a similar speed to the mean speed of winter Polar Easterlies nowadays that reduces the pressure on mid-latitude regions and ocean- surfaces to act as a sink for Westerly AAM. Increased deep tropical depressions in the tropics (never at the Equator) are also expected with a World 3C warmer than today as hotter tropical seas (with little warming in the high atmosphere) means more convection and the potential for massive releases of latent heat-energy. As far as Westerly GLAAM is concerned, a deep tropical depression is a net sink for Westerly AAM as the very strong Westerlies equatorward of the "eye" blow slightly further from the axis of Earth's rotation than the very strong Easterlies on the poleward side of the "eye": Thus more deep tropical depressions slightly weaken the tropical source of Westerly AAM, other things being equal. However, other influences in the tropics such as stronger Easterlies in the upper atmosphere near the Equator (as a result of the zone of hot, steamy rising air, the ITCZ moving well north and south of the Equator into the Hemisphere experiencing summer) would add Westerly AAM due to more Easterlies blowing against equatorial mountains. Global warming is also likely to push the zones of strong upper-atmosphere Westerlies further north and south, so that these miss major mountain areas in lower latitudes. Against that, the ITCZ moving well north or south of the Equator also encourages the normally-easterly Trade Winds to "re-curve" on crossing the Equator- leading to more extensive North West Trade Winds penetrating northern Australia or interior South America from December to March and more extensive South-Westerly Monsoon Winds over South Asia and West Africa during the Northern Summer. Hotter, steamier conditions with the ITCZ would (on the one hand) increase the strength of the easterly trade winds and the source of Westerly AAM in the tropics, but greater warming in higher latitudes- particularly over sub-tropical oceans would also help weaken the temperature and pressure gradients between the sub-tropical high-pressure belts and the ITCZ- leading to weaker easterly Trade Winds. Overall, a slight weakening of the North East and South East Trade Winds will help reduce the extent to which easterlies in the tropics and sub-tropics (both at the surface and aloft) add Westerly AAM to the global circulation. All things considered, less Westerly AAM generated by easterlies blowing over land and seas in low latitudes leaves less to be transported to higher latitudes. All these factors together- slightly weaker easterly Trade Winds, more intense tropical depressions and more vigorous monsoons in the summer Hemisphere outweighs the effects of more Easterlies and less Westerlies affecting tropical mountains in a 3C warmer world. The result is less Westerly AAM transfeered to higher latitudes and this is consistent weaker Westerlies in middle latitudes. An ice-free Arctic Ocean attracts the depressions that would otherwise move east across the far North Atlantic. This article here also lends support towards weaker Westerlies reaching western Europe (https://journals.ametsoc.org/view/journals/clim/29/2/jcli-d-15-0315.1.xml). A global climate 3C warmer than today with a totally ice-free Arctic Ocean, with weaker Westerlies from the North Atlantic (with depressions often moving north rather than east after the southern tip of Greenland) means Britain and north-west Europe will come more under the influence of blocking high-pressure systems, particularly during the winter months. Hotter conditions (and a steeper atmospheric temperature gradient) mean more sharp thunder-storms are possible in summer (bringing localised flooding), but also a lot of very hot sunny weather even across northern Britain during spells of high-pressure. Winter is likely to feature rather more frequent high-pressure systems building over northern Europe- extending westwards to bring very cold air from Russia to the UK- even with 3C global warming a week of easterlies from the far side of the Urals would still bring bitterly cold conditions with hard frost and snowfalls in the winter months. Other winters would be very mild with the high-pressure further east allowing warm south-westerlies to reach Britain (with the warmer North Atlantic encouraging heavy rainfall across the north at times). Continental Europe is likely to become quite arid, with very hot summers and dry, often bitterly cold winters: Severe droughts would become a major problem right across western Europe. Judging from the changes in positions of depressions, the reduced Arctic to sub-tropic atmospheric temperature gradients and changes in the strength and positions of the GLAAM fluxes (up and down) the Circumpolar Vortex is likely to weaken by 10% or more: This alone will make the Circumpolar Vortex more wavy and spread the sink for Westerly AAM towards lower mid-latitudes (where westerly winds do not have to blow as strongly over the surface to act as a sink for AAM)- as well as permitting depressions to penetrate the high Arctic. In a world that is 3C warmer this will not be good news for those with health problems that make them susceptible to extreme heat or cold- or for farmers and horticulturalists that depend on rain for their crops to grow.

Dear Readers The impact of increasing global temperatures over the last forty years on Arctic sea-ice cover is clear: There has been a consistent decline in sea-ice extent compared to the long-term normal (see here for an illustration: http://nsidc.org/soac/sea-ice.html#seaice). The possibility of the Arctic Ocean becoming ice-free in summer, then remaining so into the winter is one that is of increasing concern for remote communities on the Arctic coastline and for wildlife. Less appreciated, perhaps is how an Arctic Ocean free of pack-ice year round would impact upon the prevailing (and possible extreme) weather- conditions further afield. It is certain that the loss of Arctic sea-ice would occur in the context of global temperatures just 2.5 to 3C above those of today. As the Arctic warms and the edge of the pack-ice recedes north of Spitzbergen the ice-free water absorbs heat from the Sun rather than reflecting it back to space and this helps warm the local ocean surfaces further. If Greenland remains very cold and ice-covered the baroclinic zones of sharp atmospheric temperature and pressure- gradients would extend north-eastwards and northwards from the tip of southern Greenland, this would encourage more North Atlantic depressions to push deep into the Arctic. That process would, in addition bring warm southerly winds from the North Atlantic right up into the Arctic- further exacerbating regional warming. It is clear to see that if this feedback between more ice-free waters absorbing the Sun's heat in the summer, then attracting depressions into the area in winter bringing more warmth- really took off then the entire Arctic could become free of ice one summer, then remain free of ice as autumn and winter storms moved in over the ice-free areas with warm air from lower latitudes. Once the Arctic is ice-free and the surface waters stay above the freezing-point of ocean water year-round (-1.8C) the ice-free ocean would release a large amount of warmth into the low atmosphere. This would lower surface pressures but would also have a smaller warming influence on the high atmosphere over the Arctic. The main influence of the lowest 3,000 metres of the atmosphere being some 10C warmer in Autumn and 15 to 20C warmer in Winter would be a drop in average surface-pressures over the central Arctic by 15 millibars in Autumn and 20 to 25 millibars in Winter- that fact alone combined with the stronger atmospheric temperature gradient between much warmer conditions in the low troposphere and still very-cold air in the upper-atmosphere would be strongly conducive to storm activity in Autumn and Winter. The article referred to here lends support to this thesis (https://journals.ametsoc.org/view/journals/clim/31/19/jcli-d-18-0109.1.xml). In Summer, an ice-free Arctic would be little warmer than the part-thawed pack-ice there today, unless sea-surface temperatures could get well above freezing-point: It is thus likely that the Central Arctic would not experience more summer storms in a warmer world, but hotter conditions on the continents surrounding the Arctic in a warmer would still increase the crucial baroclinic atmospheric temperature contrasts to increase cyclogenesis at the margins of the Arctic- with worrying implications for coastal erosion along the Arctic coast-lines of Canada, Alaska and Russia. This still implies, for the purposes of discussing the wider implications for mid-latitude weather-conditions, a general northwards shift in storm- tracks. We now look at what the implications of increased temperatures and storminess in the ice-free Arctic Ocean mean for regions well to the south of the Arctic Circle. There is a school of thought that believes an ice-free Arctic ushers in wetter conditions with stronger winds in temperate latitudes, with severe winter cold spells becoming a thing of the past (not least because the World would be 3C warmer and middle-latitudes are not far from the unfrozen Arctic Ocean region that will be 20C or more warmer in winter). Certainly this means that any northerly winds coming from the Arctic interior will not bring severe cold to Britain during the winter months, but this does not rule out cold air coming from the east even if sea-surface temperatures around Britain are 4C warmer at the start of the winter. And there is no guarantee that that will be so because if the North Atlantic Drift weakens in response to weaker Westerlies sea surface temperatures around the UK may not be much warmer than today. The main influence of an ice-free Arctic Ocean, at least in Autumn and Winter will, from the above, be to steer the deep depressions (that normally push north-east from Iceland to north of Norway in Autumn and Winter nowadays) much more northwards along the East Greenland Coast and into the Arctic interior. Furthermore a much warmer Arctic in Winter would even ensure that the upper-atmosphere warmed a little (as cyclonic cloudy convection transfers heat into the upper-air)- increasing the 500 mb heights by 200 metres or more. That process alone would help decrease the strength of the Circumpolar Vortex by 10% or more, not least over the North Atlantic west of the UK. On the other side of the ledger, if the North Atlantic is 4C warmer in early winter that almost doubles the latent heat available to fuel deep depressions and could help tighten and strengthen the Circumpolar Vortex twice as much as the reduced Circumpolar Vortex might weaken it. That is particularly possible if Greenland is still ice-covered and Greenland/ north-east Canada still get very cold in winter, the sharp baroclinic temperature gradients in the atmosphere between Greenland/ NE Canada and a warmer North Atlantic would be a very potent source of cyclogenesis- but the question then becomes where do the depressions go, i.e. eastwards or northwards up the East Greenland Coast into the ice-free Arctic Ocean. If the depressions that normally headed just north of Norway in the past travel up the East Greenland Coast towards the North Pole in a warmer world that has very profound implications for the climate of western Europe (including the UK). Continued below.

Continued. The conventional understanding of the atmospheric sinks and sources of Westerly AAM, so that the Earth Atmosphere System conserves total axial Angular Momentum, does not necessarily hold true in a manner that some meteorologists might expect for strong Global Warming either: Strong Global Warming would lead to melting of all the ice-caps whilst engendering more frequent (and severe) tropical depressions and hurricanes. Depressions in higher latitudes depend, amongst other things, on steep upper atmospheric temperature and pressure gradients between warmth over mid- latitudes and much colder conditions over the Arctic (and Antarctic). If you warm the Arctic and remove the ice-cap then, particularly in winter, you remove a key component of that which drives deep depressions and thus furnishes strong south-westerlies in the latitudes of the UK and western Europe. An ice-free, much warmer Arctic is not likely to have "Polar Easterlies" because the upper-air would still be very cold and the warm water surface would fuel convection. Greenland, even without an ice-cap would still get very cold in the interior and this, with the ice-free Arctic Ocean (but still very cold air aloft) would encourage the formation of quite deep depressions which would move across the Arctic Ocean. Surrounding areas, such as coastal northern Siberia, Greenland and the Canadian Arctic islands would then be affected by strong Westerly winds- so the Arctic Region would (likely) become a sink for Westerly AAM- though not a major one on account of its closeness to the axis of Earth's rotation. Even so, a deep depression centred near the North Pole would have no Easterlies (as such) associated with it, the centre of the depression would invariably be north of wherever one was! In a much warmer world more (and more intense) tropical depressions are liable to complicate the picture of where the sinks and sources of Westerly AAM are. On the whole, a deep tropical depression acts as a slight sink for Westerly AAM because the very strong Westerlies on the equator-ward flank (tropical depressions can never form within five degrees of the Equator) blow slightly further from the axis of the Earth's rotation (and, thus are more effective at removing Westerly AAM) than the easterlies poleward of the eye of the deep tropical depression. That said, deep tropical depressions tend to form close to (and move westwards along) the ITCZ when the ITCZ is well north or south of the Equator in whichever Hemisphere is experiencing summer/ autumn. Thus strong surface Easterlies add Westerly AAM to the Hemisphere in summer/ autumn but strong Westerlies extending equator-ward of the ITCZ remove it even more effectively from the Hemisphere experiencing winter/ spring. For the Northern Hemisphere, more hurricanes and typhoons would help strengthen the higher-latitude Westerlies between July and October- leading to windier, wetter summers but more tropical depressions south of the Equator during the Northern winter would help weaken the mid-latitude Westerlies- as would more depressions in the Arctic Ocean. This is because the Arctic and the area between the Equator and 10S would have strong Westerly winds- acting as efficient sinks for Westerly AAM- leaving rather less Westerly AAM for mid- latitudes of the Northern Hemisphere: Ergo more blocking highs and dry colder weather from the east is likely in Western Europe between January and May. Strong global warming would lead to more warming at high latitudes as ice caps melt and the darker surface, but the Equator would warm less. However, increased CO2 levels would concentrate most of the warming in the lower atmosphere so the steep atmospheric temperature gradient driving convection in the ITCZ would increase. By the same token warmer seas in the subtropics would help weaken the subtropical highs and help to reduce subsidence there- and reduced temperature and pressure gradients from the subtropical highs to the ITCZ would help weaken the easterly-quarter Trade Winds both north and south of the Equator. On balance, there would likely be a weaker Hadley Cell and the transfer of Westerly AAM from the surface in the tropics- then to higher latitudes would be reduced. This would also support generally weaker Westerlies in mid-latitudes, as would the sharply-reduced atmospheric temperature and pressure contrast between high latitudes and the sub-tropics. Warmer ocean surfaces in mid-latitudes would also help fuel deeper depressions, particularly in autumn and winter but the reduced atmospheric temperature contrasts between the Arctic and mid-latitudes would help weaken them. Depression tracks will also tend to higher latitudes. The distribution of the sinks and sources of Westerly AAM are likely to change substantially in a much warmer world than today. A weak temperature gradient from the sub-tropics to the Arctic will make mid-latitudes less of a sink for Westerly AAM than today, but deep depressions penetrating an ice-free Arctic will also make the Arctic a sink for Westerly AAM (taking up some of the slack for mid-latitudes), rather than a source for it (due to Polar Easterlies). The influence of more (and deeper) tropical depressions means that overall the tropics will be a bit less of a source of Westerly AAM than today, even if the Hadley Cell remains similar in strength. My contention is that the Hadley Cell weaken slightly overall as the impact of significantly reduced temperature/ pressure contrasts north and south outweigh the effects of stronger convection enhancing the ITCZ. However, another impact of the ITCZ moving well north and south of the Equator (due to more continents getting hotter than the Equator in summer) will be easterlies aloft in low latitudes- adding Westerly AAM to the atmosphere where these easterlies touch mountains (i.e. the northern Andes, mountains of East Africa), but this influence will be countered by more extensive monsoon south-westerlies affecting West Africa and south Asia and monsoon north-westerlies over Papua New Guinea and the tropical eastern Indian Ocean from December to March. A warmer atmosphere will also have a deeper troposphere, particularly in northern latitudes which somewhat reduces the scope for the sub-tropical (Westerly) jet-stream to impinge on the Himalayas or the South American Andes. That removes one sink for Westerly AAM, but a weaker Circumpolar Vortex (due to a reduced poleward temperature gradient) would still encourage some depressions (with Westerlies to the south) to penetrate lower latitudes. On balance, a much warmer Earth would see a net reduction in Westerly AAM transferred to the atmosphere in the tropics, subtropics and the Arctic overall and a corresponding reduction in Westerly AAM reaching middle latitudes, at least in the North Hemisphere. Significantly, if the Arctic Ocean was totally ice-free and the Antarctic ice-sheet melted (which would raise sea-levels by almost 80 metres worldwide) there would be no Polar Easterlies as such, the Arctic would become a significant sink for Westerly AAM in winter with depressions pushing into the area. In conclusion, therefore, either serious Global Warming or a return to much colder conditions globally would see a reduction in Westerly AAM transferred from high and low latitudes to middle-latitudes- but for different reasons: For instance, strong global warming leads to stronger tropical depressions which overall act as a sink for Westerly AAM, however strong Global Cooling towards Ice Age conditions encourages an upwards (rather than poleward) transfer of Westerly AAM leading- in time- to major mountain areas in lower latitudes becoming the sinks for Westerly AAM simply because low elevations at higher latitudes are no longer in a condition to receive it (at least not during the winter months). Whatever the reasons, the result is weaker Westerlies, or even north-easterlies instead for many mid-latitude areas. Strong global warming is capable if weakening the Westerlies blowing across the North Atlantic to such an extent that much colder winters with frequent easterly winds from Russia could, paradoxically affect the UK much more often.

continued During the summer half-year in the last Ice age there will still have been enough open water over oceans (and indeed warmth over land) south of about 45N to mean that the transfers of Westerly AAM happened in a manner close to how it is conventionally understood today: That is, with Westerly AAM being transferred polewards to furnish depressions (and Westerlies to the south of them) in higher latitudes. However, the zone of Westerlies would have been closer to the Equator- 30 to 45N rather than 40 to 70N (as in summer nowadays). With the Westerlies blowing in latitudes further from the axis of the Earth's rotation they will not have had to blow as strongly to remove Westerly AAM from the Global Circulation even though, as likely a steeper temperature and pressure gradient from the subtropical highs to the ITCZ will have furnished stronger North East Trade Winds. Also, unlike nowadays, the Himalayas and Karakoram mountains would have remained under the influence of some Westerlies beneath the subtropical jet - unlike in summer today. All of this would have increased the scope for blocking patterns to persist in high-latitudes to bring dry cold Easterly winds across Europe and North America (as discussed in Nigel Calder's "The Weather Machine and the Threat of Ice"). Clearly the existence of some open water in middle latitudes and an atmospheric temperature gradient between the Arctic and mid-latitudes had to lead to the formation of depressions- how else could the ice-sheets of northern Europe and North America have been furnished with snowfalls? However, it is clear that the more southerly zone of the weaker Westerlies even during the summer in an Ice Age can still (with help from the Himalayas also acting as a sink for Westerly AAM) satisfy the requirements for a sink for Westerly AAM to match the sources (Easterlies were prevalent across both high and higher middle latitudes in Ice Age summers, as well as in the tropics), and this also provides an explanation as to why extreme drought prevailed across such vast areas of the Northern Hemisphere. Cold seas in mid latitudes and permanent ice on most land areas north of 45N will not have been conducive to deep depressions in general. However, strong temperature contrasts between the ice sheets and the warmer open North Atlantic will have furnished sufficient cyclogenesis (depression formation) in early autumn- before the sea froze over to bring snowfalls heavy enough to build up the ice over eastern Canada, but few major land areas (if any) saw sustained increases in precipitation during this period. Cold seas and oceans are not a good source of moisture and energy for depression formation (particularly where these freeze over), and this is something that is observed today. For instance, deep depressions virtually never penetrate Siberia between December and March and they weaken and fill rapidly if they penetrate interior Antarctica or- in winter- if they penetrate over the frozen Arctic Ocean. The fluxes on Westerly AAM and the constraints of the Law of Conservation of Angular Momentum are secondary to the fact that hot air rises and cold air sinks, that colder air (particularly near the surface) encourages high surface pressure and out-flowing winds whilst warm surface and low- atmosphere conditions, particularly with cold air aloft encourages depressions, surface convection and squalls. Conservation of Angular Momentum and the position of fluxes of Westerly AAM on planet Earth almost has to play second-fiddle to the thermally- direct controls caused by warm air rising and cold air sinking- and often has to work around them. continued below.

Dear Readers, I would like to explain how a fundamental feature of the Global Circulation, that of the tendency of the atmosphere to rotate with the solid Earth around it's axis of rotation accommodates changing seasons functions. I also discuss how it accommodates some of the extreme conditions deduced by paleo-climatologists to have occurred across a large area of planet Earth during the most severe phase of the last Ice Age. Drought and severe cold seem to have featured heavily in both lower and higher latitudes during the most severe phase of the last Ice Age whilst drought was a feature feature of climate in the tropics and sub-tropics. This can only be explained in terms of persistent weather-patterns that have been observed to bring such conditions during the period of modern civilisation, that of strong high-pressure over higher latitudes keeping rain (or snow) bearing weather systems away, with the high-pressure delivering cold dry north-easterly winds across large areas of planet Earth. In the tropics too, drought is today associated with a strong sub-tropical high-pressure belt that brings dry, quite strong north-east winds (or south-east winds in the Southern Hemisphere) on the equatorward side. This is associated with the zone of hot, steamy rising air associated with Intertropical Convergence Zone (ITCZ) being restricted to being very close to the Equator with monsoons failing to penetrate tropical continents to bring seasonal rains. This is also a feature of Ice Ages where West Africa and southern Asia fail to get monsoon rains because they stay cooler (or at least fail to heat up more) than the hot equatorial seas to the south. The modern understanding of how the atmosphere gains and loses Westerly Atmospheric Angular Momentum (AAM) by frictional interaction with the underlying surface is not consistent with a global climate whereby cool dry north-easterly winds can prevail over more than about 65% of the Earth's surface because of the Law of Conservation of Angular Momentum. It is then argued that because the atmosphere continues rotating with the Earth and because outside forces (from lunar tides, meteorites, etc.) are miniscule compared to the mass of the Earth's atmosphere and the momentum exchanges with the underlying surface, that what Westerly AAM is gained by the atmosphere in the tropics, subtropics and polar regions (due to the Polar Easterlies) has to be returned to the surface in middle latitudes. The atmosphere in low and very high latitudes does gain Westerly AAM through the frictional impact of surface easterlies on the seas and lands over which they travel and, indeed, Westerlies in higher latitudes, again through their frictional interaction with the underlying surface over which they blow, make those middle latitude locations the sink of Westerly AAM. However, strong Westerlies in higher latitudes in autumn and winter are consistent with deep depressions which draw not only on sharp upper atmospheric temperature and pressure gradients aloft (i.e. through a strong Circumpolar Vortex) but also a source of warmth and latent heat to fuel these depressions effectively. And paleo-climatologists have deduced that winters at the height of the last Ice Age were dry and bitterly cold in the North whilst there were also strong dry North East Trade Winds bringing drought across Africa, southern Asia and central America with greater volumes of dust transported across the Atlantic from the Sahara to Brazil (Nigel Calder's 1974 publication on "The Weather Machine and the Threat of Ice" covers all these details). And the Law of Conservation of Angular Momentum does not preclude the possibility that much stronger Westerlies could dominate in the Stratosphere and upper atmosphere whilst Easterlies predominate in the lower atmosphere and the Earth's rotation slows down enough to add a few milliseconds to the Length of Day: What matters is that the entire Earth Atmosphere system conserves axial Angular Momentum in the absence of outside forces. Under such conditions, with very strong Westerly winds aloft high mountain areas alone (like the Himalayas) would become the sink for Westerly AAM as very strong Westerly winds blasted them at times. In the absence of mountains, Westerly AAM would be brought down to the surface in areas of strong atmospheric subsidence when and where day-time solar heating of the surface and lowest layers of the atmosphere is sufficent to bring about stronger surface boundary layer convection- i.e. subtropical land areas in the Spring and Summer (beneath the descending air of a strong subtropical high-pressure belt). Such westerly (or more likely with the air moving equatorward with higher surface pressure to the north, north-westerly) winds would be very strong and return to the Earth Westerly AAM imputed to the atmosphere by north-easterlies over the rest of the Northern Hemisphere over the preceding year. Such a situation would be more likely to develop in a severe Ice Age winter when extremely cold, dense air covers all middle and high latitude areas, the troposphere would correspondingly become a bit thinner north of the sub-tropics then the upper-air thermal and pressure- gradients become further strengthened around 25 to 30N: That would further increase the speed of the subtropical jet-stream and the westerly speed of the subsiding air beneath it. Either way, in a severe Ice age Winter we have a situation whereby Westerly AAM is transferred from the surface into the atmospheric circulation (due to extensive Easterlies) , then is transferred upwards rather than polewards. That is not inconsistent with the Law of Conservation of Angular Momentum, but the sinks for Westerly AAM will also (likely) be in the tropics or sub-tropics (due to very strong Westerly jet-streams blasting subtropical mountains or (with daytime heating below) brought down to the surface in violent dusty squalls beneath the strongly- descending subtropical high-pressure belt (at about 25N). The Ferrel Cell in middle- latitudes, with surface south-westerlies and winds returning from higher latitudes would almost certainly cease to exist in a severe Ice Age winter (with all seas and lands frozen north of 30N)- to be replaced by a single Direct Cell extending from the Polar Regions to south of the Equator. Today, it is the returning flow of air from high-latitudes aloft- becoming relatively less "Westerly" as it moves into lower latitudes that today weakens the Westerlies moving north aloft from the Hadley Cell (by colliding into them), so that the air descending in subtropical highs does not have a strong Westerly component by the time it reaches the surface. If the mid-latitude and high-latitude oceans and lands are all frozen there is no Ferrel Cell, the air descending from beneath the subtropical highs moves strongly from the West as it descends- and it becomes subtropical Mountain Ranges like the Himalayas, Karakoram mountains and the High Atlas that the Westerlies hit (and are slowed down rapidly by). Unless the upper- air is much colder still (so as to encourage convection and cyclogenesis), frozen lands and seas with all the low- atmosphere being well below freezing-point do not lead to depression formation (or, with it, strong Westerlies on their southern flanks). continued below.

continued Even in the absence of mountains in the Northern Hemisphere, if all surfaces and land areas north of 25N were frozen, then the strong North-East Trade winds in the tropics that would result would still pump lots of Westerly AAM into the atmosphere, yet this would still be unlikely to lead to depressions forming in higher latitudes. This is most certain to be the case in winter when extremely frigid conditions with high-pressure would be liable to dominate and prevent any depressions or Westerlies touching the surface. Instead, it is likely that the Westerly AAM would be forced to accumulate in the upper-air until early Spring when conditions become favourable in low latitudes (under the rapidly- descending part of the Hadley Cell) for daytime surface heating over land to permit some of the fast-moving air to reach the surface- bringing very strong Westerly winds (or likely north-westerly winds as the Hadley Circulation returns to the Equator at low- levels). Such very strong daytime surface Westerlies, between (say) 20N and 30N during Spring could cancel out north-easterlies in remaining latitudes over the rest of the year. Strongly- accumulated Westerly AAM in the upper- atmosphere is liable to be "thrown back" towards low latitudes to make contact with the surface there- if surface and low- atmosphere conditions were very much colder in middle and higher latitudes. There is nothing in the Laws of Physics to preclude the global climate from becoming like this with the right climatic conditions: Indeed, climatologists have established that there was extensive dryness across large parts of the world, prevailing strong Easterlies in both higher and low latitudes (at least in the low atmosphere), during the coldest phase of the last Ice Age. This has been observed in the Southern, as well as the Northern Hemisphere. The extensive Westerly AAM being put into the atmosphere by stronger North Easterly (and in the Southern Hemisphere, South Easterly) Trade Winds clearly did not lead to stronger (and more extensive) Westerlies in higher latitudes then. There is nothing in the Law of Conservation of Angular Momentum to suggest that more extensive Easterlies below cannot be compensated by much stronger Westerlies aloft (rather than in higher latitudes) with the high mountain areas like the Himalayas and the Bolivian Altiplano/ North Chilean Andes being the sinks for Westerly AAM rather than the higher latitudes. Icy oceans and frozen lands at higher latitudes are poor sources of energy for deep depressions to form and bring moisture- laden Westerlies. However, for sure, in the absence of significant amounts of Westerly AAM being lost to the Earth- Atmosphere system (and it is invariably insignificant- except were a large meteorite to careen through the upper atmosphere), then the manner of the exchanges of Westerly AAM between the surface and atmosphere vary considerably with changing climatic conditions, with the seasons and within seasons. The little illustrations above- showing Westerly AAM being transferred to higher latitudes (and especially in Winter) are not always a given- and they probably do not represent what happens during the coldest winter in an Ice Age (for example). Under extreme conditions, like those I have illustrated, the tropical and sub-tropical mountains (i.e. those between 30N and 30S) can become net sinks for Westerly AAM before the Westerly AAM can even reach higher latitudes.

continued However, the manner in which Westerly AAM is returned to the Earth's surface varies with the seasons and is also dependent on whether conditions are such at higher latitudes to favour the formation of depressions, upon which strong Westerly winds are dependent. In winter the frictional impact of stronger North East Trade Winds between the cooler sub-tropics and hot, steamy Equatorial zone add Westerly AAM to the atmosphere at a higher rate as these blow over land and oceans, than in summer. However it does not follow that higher latitudes are always the sink for such Westerly AAM: Indeed the atmosphere can merely store this Westerly AAM leading to much stronger Westerlies in the upper troposphere/ Stratosphere whilst easterlies persist below and the Earth's rotation slows down by a millisecond or two- that is, until there is somewhere at the Earth's surface where conditions become suitable to act as a sink for Westerly AAM. The overall axial Angular Momentum of the Earth-Atmosphere System can still remain constant and the Law of Conservation of Angular Momentum is not violated by the Stratosphere having Westerlies blowing at hundreds of miles per hour whilst there are more Easterlies below and the Length of Day increases by one millisecond. There are locations in higher and middle latitudes in the Northern Hemisphere that do not get Westerly winds in the winter months, which normally get winds from north or east. Eastern Siberia and Mongolia are amongst such locations and, of course almost all of Russia and continental Europe come under the influence of bitter easterly winds at times. Westerly AAM is still being pumped into the troposphere by the frictional influence of North East Trade Winds at those times and also, one must assume, by these winter-time easterlies at higher latitudes too. So what happens to the Westerly AAM pushed into the atmosphere? A useful little weather website called Windy (see here: https://www.windy.com/ ) can provide fascinating insights at such times, as I observed in January/ February 2021 when all of northern Eurasia was under the influence of intense cold associated with Arctic and Siberian blocking highs: The Himalayas and High Tibet become a major sink for Westerly AAM when severe weather pushes south and west across the Euro-asiatic continent in winter as Westerly wind speeds high over the subtropics increase sharply. Very cold conditions with extensive easterlies and northerlies in higher latitudes can also lead to an increase in the strength of the North East Trades, both of which would add Westerly AAM until another sink for Westerly AAM arises just south of the Equator when the Intertropical Convergence Zone (ITCZ) is pushed well south of the Equator: Where and when the surface North East Trades overshoot the Equator moving south, the changed influence of the Earth's rotation on the movement of air causes these winds to become north-westerly winds (these remove Westerly AAM through friction with the underlying surface). Westerly AAM being pumped into the atmosphere by the frictional impact of tropical Easterlies is not the only prerequisite for wet, windy Westerlies to affect higher latitudes: It is one of them. The other prerequisites are for suitable temperature and pressure contrasts in the atmosphere that favour the formation of depressions- and without depressions (or at least a sustained fall in surface pressure with latitude) there can be no Westerlies, and also for a source of energy: Depressions need energy- warmth from an ice- free water surface for latent heat (or land warmed by the Sun). If there was just one big continent north of 25N- or the Atlantic and Pacific oceans north of these latitudes were frozen over- no depressions would form in higher latitudes in winter. Instead the low-atmosphere over all middle and high latitude areas would become extremely cold under one large area of intense high-pressure (greatest near the North Pole): This would lead to very cold surface north- east winds which would also have the effect of strengthening the North East Trade Winds through the injection of colder air from high latitudes. Would would happen to all the Westerly AAM put into the atmosphere? In this scenario, with all middle and high latitudes frozen, the Hadley Cell would be associated with stronger Westerlies aloft, particularly where the upper-air approaches the sub-tropics. The troposphere over the frozen middle and high latitudes would be shallower and the sub-tropical jet-stream would be stronger (and a bit lower) as a result. The descending air over the sub-tropics would (initially) be moving from west to east very rapidly (probably at over 200 mph) but it would not be slowed by air moving equator-wards from higher latitudes aloft (a feature of warmer conditions with depressions at higher latitudes), the subsidence would also be much stronger than nowadays and the very strong subsiding Westerlies would not really start to lose their speed until they reached the zone where the atmospheric pressure gradient was such that it no longer supported them. So, 200 mph Westerly winds over the Himalayas and Karakoram mountains, with 100 Westerlies during the day affecting High Tibet (even in January, the Sun has sufficient strength at 30N - even over an icy surface to heat the surface and lower air and remove any temperature inversions that could keep such winds from directly impacting the surface!). These winds, consisted of subsided air would be dry and (at this elevation) very cold and, since the frictional impact of the wind increases with the square of their speed, then even though the Tibetan plateau and Himalayas covers just 0.5% of the Earth's surface and the air density just half of that at sea- level at 6,000 metres, such Westerlies would be strong enough to counterract low-level north-easterlies elsewhere in the Northern Hemisphere- even if (as likely) the North East Trade Winds would have a mean speed of 30 mph between 30N and the Equator. continued below

Global Atmospheric Angular Momentum (AAM) is a fascinating subject because it is very central to the type of weather that is experienced over much of the Earth's surface, particularly at higher latitudes. In essence, what goes up must come down, so if the atmosphere gains Westerly AAM with respect to the Earth's surface in part of the World, it must lose it elsewhere. Much is made of the fact that the Earth- Atmosphere system as whole must maintain the same level of axial Angular Momentum overall- through rotation of the Earth and atmosphere from west to east- for the Law Conservation of Angular Momentum to be observed: However that is not strictly true. Total Angular Momentum must be conserved only in the absence of outside forces acting on the Earth- Atmosphere System. There are outside forces, chiefly the gravitational effects caused by the Moon (and to a lesser extent the Sun) as the Earth rotates: The Earth (and atmosphere) has to rotate through "tidal bulges" caused to oceans and atmosphere by the Moon and Sun, which leads to a mean increase in the Length of Day by about one millisecond every fifty years. Additionally, meteorites reach the Earth from outer space and can bring small changes in the total axial Angular Momentum of the Earth-Atmosphere system, as can the Solar Wind. Atmospheric out-gassing to space involves the loss of one ten-billionth of the mass of the atmosphere each year, so you are dealing with the total axial Angular Momentum of this in addition to the remainder of the Earth-Atmosphere System remaining constant. The impact of all these influences however, are miniscule compared to the mass of the atmosphere, at least under current global climatic conditions. continued below

There has been quite a few high-profile big eruptions in recent months, each of which has led to volcanic dust ejected to over 10,000 metres' elevation: La Soufriére is the latest, with dust reaching over 13,000 metres' elevation. In March there was Sangay in Ecuador (dust reaching over 12,000 metres) and Mount Sinabung (Sumatra) blew its top at the beginning of March , again with dust reaching over 12,000 metres. At the end of November/ early December 2020 two powerful volcanoes (Semeru and Lewotowo in Indonesia) blew their top and each pushed volcanic dust to over 14,000 metres. The impact of these volcanoes, all fairly close to the Equator and in the vicinity of the Intertropical Convergence Zone (ITCZ) will have been significant. In terms of cooling the globe, even quite large amounts of dust don't have a major impact directly. The upper atmosphere ends up absorbing heat from the Sun that otherwise would reach the surface- and that warmed upper-air eventually descends in the subtropical high-pressure belts or finds it's way into the Westerlies. However, just half a degree of warming of the Equatorial upper- atmosphere (combined with a similar amount of cooling below) leads to a weakening of the ITCZ by reducing the temperature lapse- rate in the atmosphere in a part of the world normally conducive to deep convection. Since it is deep convection that normally drives the ITCZ then volcanic dust in the high- atmosphere over the Equator such that there is a 0.5C warming aloft and 0.5C cooling near the surface could weaken the ITCZ- and the attendant Hadley Cell- by 10% or more. Since the atmosphere is often conditionally unstable a reduction of the temperature gradient between the top and bottom of the atmosphere by 1C- or just under 1% (the top of the troposphere over the Equator is often below -80C but near 27C at the surface) has a much bigger impact than a 1% drop in the atmospheric temperature lapse- rate would suggest. In addition to this, La Nina has been dominant in the eastern Equatorial Pacific- with relatively cool ocean- surfaces further reducing surface temperatures near that part of the ITCZ. Thus, there has been less convection along the ITCZ, a weaker Hadley Cell and (crucially) weaker transfer of Westerly Atmospheric Angular Momentum to higher latitudes aloft. So, you end up with a situation whereby a series of powerful volcanoes like La Soufriére (with the help of La Nina) leads to weaker Westerlies and a weaker, wavier Circumpolar Vortex in higher latitudes and (with it) a higher propensity to High-Latitude Blocking Highs that displace the Westerlies from countries like the UK and allow much colder air to penetrate south from high latitudes. Thus, indeed there is a link between powerful volcanoes (if they erupt near the Equator) and increased cold- spells in mid- latitudes, though not so much for the reasons that one might first suspect. It could be that these volcanoes, along with La Nina, have helped to bring about the coldest winter since 2010-11 and also the almost three weeks of dry cold weather with plant-decimating late spring frosts across large areas of western Europe this month.