The coldest/hottest you could possibly get in a calendar month.

[CryoraptorA303]

 Geordiesnow I feel another 2019 coming, god forbid. I would genuinely rather another 2022, or maybe even a 1995 or 1976, than go through 2019 again. Endless disgusting humidity and the late July heatwave had the grossest conditions I have ever lived through. The only thing I could think of being genuinely worse than 2019 is some sort of fusion between 2019 and the August 2020 heatwave which had even worse humidity but slightly lower temps. Some sort of August 2003-esque heatwave which was also humid being thrown into the hat would be even worse.

It's quite something to see that a summer that has more than one extreme humidwave like this and also possibly be average or wetter than average is a serious possibility, from what we've seen so far. 2019 nearly pulled it off; were it not for the ridiculously strong North Sea undercurrent, we would've had a massive humidwave in late June possibly defeating Coningsby before it even happened, and we would've ended up seeing two giant humidwaves in the same summer, a summer that was considerably wetter than average. If the August heatwave was more severe it could've been the third one. This summer could be the one to do it. I suspect absolutely no one would be happy with this outcome.

[cheeky_monkey]

 LetItSnow! i could not find a January here that even got close to -5c as a mean average..this year in what has been one of the mildest winters on record...the January mean was -15c

[David Bruce]

It's a sign of the accelerated warming during the past few years that hotter 850s airmasses are developing earlier and earlier in the year and also spreading further and further N.  I wouldn't be surprised if 2024 breaks more heat records in Europe and UK. Hottest year in UK since records began, of that I am already pretty confident. 

David 

[CryoraptorA303]

 David Bruce I'm of the opinion that such is almost a guarentee, daily minima appear to be indefinitely above average. The weekend appears to be mounting a serious challenge to the April daily minimum record in east Kent or East Sussex. Even if summer is mild, daily minima will be very high and we'll see a rival to 2023's final total. If 2023 had another big heatwave in July or August or didn't have one of the brief colder spells in October or November, that would've almost certainly tipped the balance and led to 2023 surpassing 2022.

A humid summer like 2019 with extreme humidwaves upscaled to what we've been seeing in the past two years will essentially guarentee we surpass 2022 even if one of the autumn months inc. December are a bit on the chilly side, remember December 2022 had that cold snap in the first half and 2022 still surpassed 2014. January and February 2022 weren't particularly warm either, just slightly above average. If I had to guess, I'd have to assume 2019 didn't surpass 2014 because of that spell in early April and November mostly being a bit below average. It must've surpassed 2018 and gotten extremely close to 2003 if not surpassing it.

I also wouldn't rule out Coningsby being defeated this year in a humidwave, 2019 had Cambridge marginally defeat Faversham despite being a much wetter year than that up to that point. Since 1990, every year that set some kind of winter all-time record aside from 1998 went on to break the all-time record in the summer. 1990 set the then-February record, 2003 tied the January record and set the English one, 2019 broke the February record (and later broke the December record too), 2022 broke the New Year's Day record by quite a margin, and now 2024 has broken the January record by the same margin that Coningsby defeated Cambridge by. 1998 is the only one that broke a winter record (February) and then had a mild summer with no major heatwave. I'd say the chances are stacked quite against us...

[LetItSnow!]

 CryoraptorA303 I sort of feel like 1990 was the first version of our sort of typical late 2010s/2020s summer in a way; one poor month, one mixed month that ends up with a very hot spell and then one month with a serious heatwave. Indeed, I've seen people discuss summer 1990 very similarly to summer 2019; no one can seem to make up their mind if it was good or mixed! 

[CryoraptorA303]

 LetItSnow! I can't say I've seen anyone discuss 1990, it seems rather forgotten for its achievements. I suspect 2019 will end up similarly in 10-15 years time once we've had a couple more serious heatwaves that overshadow it in duration or severity. 2019 will be the last heatwave year to come up after 1990.

[B87]

 CryoraptorA303 2019 wasn't that bad, yes the first half of June was generally awful, but after that it was generally warm, dry and sunny through July and August. 

[CryoraptorA303]

 B87 It was also very humid and had stormy breakdowns for many. My sleep quality was extremely poor that summer. Nights felt unbearably humid for a lot of the summer and the crane fly season coming early that year meant I had to close my windows from ~6pm even when it had been hot by day and was staying warm at night. I remember during that brief June heat spike there were crane flies everywhere (surely among the hottest temps European crane flies have ever experienced?), a very bizarre sight, and I was forced to shut the windows while it was still extremely warm in the late evening. July 25th 2019 is the worst climatic day of my life, 36°C in the day at moderate humidity and then still high-20s to low-30s in the evening at extremely high humidity, absolutely gross and I'd take a consecutive week of Coningsbys over going through that summer again.

[LetItSnow!]

 CryoraptorA303 How lovely those 1960s summers must have been… Some didn’t exceeed 25C! What a different world we live in now. Makes you wonder what the theoretical lowest possible maximum could be for a summer, in keeping with the original theme of the thread. 

Im loving the open discussion here though. 

[CryoraptorA303]

2 minutes ago, LetItSnow! said:

How lovely those 1960s summers must have been… Some didn’t exceeed 25C! What a different world we live in now.

In London anyhow, elsewhere they at least got higher than that. Even then, an entire four years out of that decade didn't reach 30°C, and 1962 only reached 27.8°C at Writtle, the lowest in living memory and second in reasonable history only to 1879's 26.8°C. Also interesting is it was a September annual maximum, so the actual summer itself may well have not exceeded 25°C anywhere. 1965 is another contender as it's maximum was on May 14th, the earliest in reasonable history, and if I recall, that summer was extremely cool, so that stands a decent chance of not going above 25°C anywhere.

The other interesting point to be made about the 1960s summers, they may have been very cool by today's standards, but as far as I'm aware they also tended to be dry, which I have to assume would also imply at least a few sunny ones, so perhaps these summers may have not actually been too unpleasant?

9 minutes ago, LetItSnow! said:

Makes you wonder what the theoretical lowest possible maximum could be for a summer, in keeping with the original theme of the thread. 

Depends on the severity of the eruption or asteroid impact. I imagine it failed to exceed freezing for a few summers during the K-Pg extinction!

In all seriousness, going back to 1875, 1879 was as low as 26.8°C and the next lowest was a full degree higher, so this was probably near the natural limit of how low a max could realistically be. Today I'd assume that'd translate to 28-29°C, so a sub-30°C annual maximum in the near future would likely be 1-in-100 year summer or near enough. By 2050 if it hasn't happened I'd have to assume it's virtually impossible without an outside factor like an eruption at that stage.

[LetItSnow!]

 CryoraptorA303 Perhaps a thread deep diving the summers of the 1960s would be interesting. I get a kick out of rummaging through data like no one else so I'd love to do it, just if anyone else would read it. You're right to suggest that they weren't always bad. Some truly were (1965 is a good example and just a plain odd year) but some were cool but weren't always low pressure dominated. Relates back to what I was talking about with Summer8906 how older summers had less forcing due to a weaker Hadley Cell so polar maritime air was more frequent which while cool, can be quite bright in the summertime. Also convective. It wouldn't surprise me if some of those 1960s beat recent summers for sunshine. 

[raz.org.rain]

 CryoraptorA303 and that's assuming that an eruption actually does result in cooling. Volcanic eruptions can have the opposite effect and induce a greenhouse state.

Funnily enough, volcanic eruptions and asteroid impacts have been suggested as contributing factors for triggering previous runaway global warming events.

[LetItSnow!]

 raz.org.rain I think it's a case of the specific type of eruption. Many cause cooling due to the reflection of sunlight back into the atmosphere, but some increase the temperature I think due to water droplets or something. I'm not a scientist as you can see. The latter may be giving some extra oomph to the warmth across the world right now. Part of why I think 2025 and 2026 may be a temporary pause as the effects of that fade out a little and other factors too (Famous last words). In his case though he meant the traditionally understood eruption.

[WYorksWeather]

 LetItSnow! Essentially, most volcanic eruptions result in cooling. There's still no consensus on Hunga Tonga, though it may have had a warming effect.

The climatic effects of volcanoes are dependent on the amount of material they inject into the stratosphere. Any material not injected into the stratosphere doesn't have a significant effect as it rains back out of the atmosphere too quickly, and it takes a pretty large volcanic eruption to inject a substantial amount of material into the stratosphere - typically events with a Volcanic Explosivity Index (VEI) of 5 or higher. These events are fairly rare, on the order of years to decades.

So, assuming you have such an event, the cooling effect results from the injection of sulphur dioxide (SO2) into the stratosphere, which scatters and reflects incoming shortwave radiation from the Sun, and also aids in the formation of reflective clouds. The warming effect results from the injection of water vapour into the stratosphere, which absorbs outgoing longwave radiation from the Earth's surface.

For most eruptions, cooling far outweighs warming. The reason Hunga Tonga may have been different is that it injected relatively little SO2 for the size of the eruption, and a fairly large amount of water vapour. Water vapour injected high up into the stratosphere may stay there for several years. We will probably only know for certain until a few more years have passed.

There is precedent for volcanic influence on the study of climate change - in the early 1990s the eruption of Mount Pinatubo (VEI 6, which is very rare), which was the largest since 1912, had a huge impact on global climate, reducing global temperatures by around 0.2 to 0.4C for over a year.

The most famous event for which we have reasonable records, though, is the eruption of Mount Tambora in 1815, the largest for over a millennium, which led to the infamous Year Without A Summer in 1816. The associated global temperature drop was 1C or more for several years, but most notably in 1816, which included the coldest CET July ever recorded.

 

[CryoraptorA303]

 raz.org.rain  LetItSnow!  WYorksWeather

It also depends on the timescales we're talking about.

As far as I know, most greenhouse events that have been associated with volcanism are long-term events lasting thousands or millions of years, where an elevated rate of volcanism led to a long-term increase of greenhouse gases and caused global warming. The P-E thermal maximum is probably the last example of this in our history. The Siberian traps and associated extinctions were obviously the most extreme example of this.

I haven't heard of any asteroid impacts leading to warming, but I suppose its possible if the impact is antipodal to a volcanic chain and causes a sudden explosive rise in volcanism.

My personal hypothesis is around 260 million years ago, some millions of years before the Capitanian and P-T extinctions, the Solar System had a close encounter with another star on the scale of the encounter we will have with Gliese-710 in the next ~1.3 million years, perhaps a star more massive than G-710 or even the Sun, which led to a much-elevated rate of cometary impacts over the next few millions of years as the passing star heavily disrupted the Oort Cloud, and these impacts contributed to the severity of the Siberian traps and led to the extinctions being as severe as they were. I believe a suspected large crater has actually been found around the antipode of where the Siberian traps would have been in life.

Hunga Tonga, if it is indeed significantly contributing to warming, is certainly not helping with climate change and will help to spearhead it over the next couple of decades. I suspect the effect is overall quite mild but we will have to wait and see.

Edited April 2 by CryoraptorA303

[Relativistic]

 CryoraptorA303 Theoretical physicist Lisa Randall speculates that fluctuations in local dark-matter density may have been responsible for disturbing the Oort cloud in the way you suggest. She has a book called Dark Matter and the Dinosaurs where she gives more details.

[CryoraptorA303]

 Relativistic That seems a lot more speculative than a stellar encounter. Stellar encounters are something that is established to be a likelihood over hundreds of millions of years; we still have very little, if any understanding of dark matter, far too little to speculate involvement with mass extinctions.

The dinosaurs lived after the P-T extinction and went extinct (save for avian dinosaurs) during the K-Pg. The impact was recent enough for us to reconstruct the contents of the impactor and it was asteroidal; it did not have origins in the far outer Solar System. Recalling from memory, a study a couple of years ago identified the impactor as a fairly uncommon subtype that has origins in the near outer Solar System. The study proposed that this kind of asteroid reaches the inner Solar System through interactions with Jupiter and this results in an Earth impact every 300 million years or so. Importantly this would make any impacts dated to the Permian unlikely to have this origin. Dark matter involvement with the Chicxulub impactor seems unnecessary to explain it. We still have no real explanation for the severity of the Siberian traps, and for me, a stellar encounter, possibly involving a multiple system which would be particularly disruptive, seems to be the most likely explanation, given what we now know about the likelihood of close encounters like this. Of course this is unfalsafiable as it is impossible to reconstruct the movement of all ~400 billion stars and numerous other objects in the Milky Way back 250 million years with any degree of certainty.

[Relativistic]

 CryoraptorA303 Yes, I'm aware it's speculative, and so is she (hence my wording). I haven't read the book but she acknowledged this in a recent interview. You've convinced me against the idea.

[LetItSnow!]

This model run seems frighteningly close to our discussion the other day! Perhaps I wasn't entirely on the silly juice  (I don't think it'll verify though) @WYorksWeather

 

[Azazel]

 CryoraptorA303 I would take it - 2019 had some spectacular thunderstorms for my area and some actual heat.

[CryoraptorA303]

 LetItSnow! What the is that?!

Surely that'd translate to widespread 30-32°C depending on air pressure and wind direction?

[raz.org.rain]

 Azazel 2019 seems to be one of the more viable outcomes for summer so far. As I've said elsewhere, I believe heat will be a consistent theme regardless of whether or not it's dry or wet, the incoming 850hPa temperature spike and growing Azores influence is a good demonstration of what we can expect throughout summer. This would be great if it's +30°c you're after, but terrible if you're not a fan of humidity and overcast skies.

[Azazel]

 raz.org.rain I do struggle with humidity to be fair so I just make sure I take all the steps possible to mitigate it. Drink a cosmic tonne of water etc. humidity means the chance of big storms so I’m all for it!

[CryoraptorA303]

 Azazel Storms aren't what we need this year though, we need at least two out of the six warmer months to be notably dry and warm. If the groundwater isn't dealt with before summer then things will go the way of 2019 and become extremely humid once the heatwaves inevitably start rolling in.

Honestly at this point I'd prefer it if the rest of April was dry so we ended up with drier than average, May and June are at least average but preferably dry and warm, July is very dry and warm, August even drier and very warm to hot and September is the driest and hottest on record, with the hottest and driest weather of the year hitting outside of the July-mid August window for maximum temps. Some sort of August 2003/1995 cross but in September without any thundery breakdowns. We've now had two Marches in a row that were more like November, had an April last year that felt like an October, so why can't we have a September that is more like a dry and hot May or June? Bonus points if September just about edges out August and is the hottest month of the year.

Edited April 4 by CryoraptorA303

[Azazel]

 CryoraptorA303 don’t get me wrong I would love for it not to rain again until Christmas if I had my way