Target Atmospheric CO2: Where Should Humanity Aim?

[biffvernon]

Jim Hansen et al.

New paper, summary:

Paleoclimate data show that climate sensitivity is ~3°C for doubled CO2, including only fast

feedback processes. Equilibrium sensitivity, including slower surface albedo feedbacks, is

~6°C for doubled CO2 for the range of climate states between glacial conditions and icefree

Antarctica. Decreasing CO2 was the main cause of a cooling trend that began 50

million years ago, large scale glaciation occurring when CO2 fell to 425±75 ppm, a level

that will be exceeded within decades, barring prompt policy changes. If humanity wishes to

preserve a planet similar to that on which civilization developed and to which life on Earth

is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to

be reduced from its current 385 ppm to at most 350 ppm. The largest uncertainty in the

target arises from possible changes of non-CO2 forcings. An initial 350 ppm CO2 target

may be achievable by phasing out coal use except where CO2 is captured and adopting

agricultural and forestry practices that sequester carbon. If the present overshoot of this

target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects.

The next 35 pages:

http://www.columbia.edu/~jeh1/2008/TargetCO2_20080407.pdf

(3.6mb pdf)

[biffvernon]

And Gavin Schmidt has kicked off the discussion at RealClimate

[HighPressure]

I will have a read but to my mind atmospheric CO2 levels depend largely on the oceans ability to soak it up and we are seeing that fail. A reduction in emissions may not yield a reduction in atmospheric levels if our oceans continue to decline?

This comment:

"If the present overshoot of this target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects"

In my opinion based on what science understands the most likely outcome of increased warming is for the ocean currents to shut off. Now I am not saying that won't be catastrophic but not in the sense portrayed above?

[jethro]

I admit to only briefly scanning that article but a couple of things spring to mind....

"must face the uncomfortable fact that industrial civilization itself has become the principal driver of global climate"

So how come a perfectly natural phenomena such as La Nina, can in the space of a few months, overturn the warming temperatures? Surely that indicates, that despite increasing emissions, despite the urge to believe we are in control, we can have an impact; Mother Nature is still firmly in control? The article and Hansen continue down the vein of us being the most important factor in climate, our actions are the driving force; patently we're not.

Disappearance of ice caps; completely ignores the peer reviewed papers from the likes of Polyakov who demonstrate that at most, warming temperatures due to emissions may, possibly, be enhancing a natural pattern which has existed for centuries. The ocean currents have cycles, they have been in a positive phase, as they were earlier in the 20th century.

My mind continues to boggle at the belief that we, as a species, are in control of climate...

[Devonian]

I admit to only briefly scanning that article but a couple of things spring to mind....

"must face the uncomfortable fact that industrial civilization itself has become the principal driver of global climate"

So how come a perfectly natural phenomena such as La Nina, can in the space of a few months, overturn the warming temperatures? Surely that indicates, that despite increasing emissions, despite the urge to believe we are in control, we can have an impact; Mother Nature is still firmly in control? The article and Hansen continue down the vein of us being the most important factor in climate, our actions are the driving force; patently we're not.

Disappearance of ice caps; completely ignores the peer reviewed papers from the likes of Polyakov who demonstrate that at most, warming temperatures due to emissions may, possibly, be enhancing a natural pattern which has existed for centuries. The ocean currents have cycles, they have been in a positive phase, as they were earlier in the 20th century.

My mind continues to boggle at the belief that we, as a species, are in control of climate...

My mind boggles at the idea we don't have an effect. Surely, even if one refuses to accept the effect of anthro ghg's every good sceptic knows about UHI

[jethro]

My mind boggles at the idea we don't have an effect. Surely, even if one refuses to accept the effect of anthro ghg's every good sceptic knows about UHI

Having an effect, is a world away from being in control. I agree we have an impact, but in control?? Over-riding all natural drivers? Never in a million years.

[Devonian]

Having an effect, is a world away from being in control. I agree we have an impact, but in control?? Over-riding all natural drivers? Never in a million years.

Long time 'never in a million years'.

So, you wouldn't say scientist need open minds then?

[biffvernon]

So how come a perfectly natural phenomena such as La Nina, can in the space of a few months, overturn the warming temperatures?... My mind continues to boggle

What your boggling mind seems to have failed to grasp is that if we measure the temperature of the air only, we fail to see the heat that has gone below the ocean waves. The oceans are a truely mind-boggling heat store - there is a lot of water and water has a very high heat capacity. Atmospheric warming is one thing, global warming is something very different as it includes the water.

Unfortunately for all of us, the more research is done the more it appears that Hanson et al are right. His analogy of World War II has merit. In the 30's there were plenty of people who took a relaxed view of the future while some predicted dire catastrophe.

[jethro]

Dev, everyone needs an open mind, including Hansen.

We are not in control of the climate. Anyone who claims we are is IMO barking up the wrong tree. It's an exaggeration used regularly to assert the need to reduce CO2 levels. Yes, we need to reduce emissions, yes we need to look after the planet, yes we need to act with the utmost respect for the Earth and everything on it but placing your eggs all in one basket and asserting it is the be all and end all, that it is THE over-riding factor, that we are in control is absurd.

Biff - my boggling mind fully grasps the role of oceans, indeed I have asserted long and hard on this forum that it is an oft over-looked factor. Again, time and again we have been told the sinks are failing, we are in control - we are not. There is recent evidence of cooling oceans temps and CO2 levels at Mona Loa have decreased accordingly. Have we decreased emissions? Have we caused this effect? No, we have not, nature has. We're in the middle of a La Nina, reasonably strong but not staggeringly so, but still strong enough to impact on global temps on a fairly impressive way. Blast has said time and again that we have entered the perturbation phase of El Nino/La Nina, we can expect more La Ninas, fewer El Ninos, this will result in more cooling periods, perhaps stacking up to an overall reduction in global temperatures. This is natural, the last thirty odd years we have been in a positive phase which has NATURALLY increased temperatures both of the oceans and the atmosphere. Look up the Great Climate Shift in 1976, it was a step change which has been fully documented and yet this is rarely, if ever factored into global temps. The last thirty years is used as a trend to demonstrate OUR impact but, again IMO, without decoupling the natural warm phase factor, we cannot hope to have a realistic view of what our input really is, or has been.

[biffvernon]

Of course we're not in control of the climate. Would that we were. We've chucked a great big spanner in the works and our best hope is to attempt the almost impossible task of sticking our hand in and retrieving as many of the spanner bits as we can. Let's hurry up before it's irretrievably lost. Shame on those who are still intent on throwing more spanners in.

[Essan]

We are not in control of the climate. Anyone who claims we are is IMO barking up the wrong tree. It's an exaggeration used regularly to assert the need to reduce CO2 levels.

But carbon emission are just one of many ways in which we affect the climate - are you saying, everything, in combination, still has no effect?

You must at least accept regional anthropogenic climate change Why so hard to see that lots and lots of regional changes add up to a global change?

[jethro]

Biff - the article you posted quoted "must face the uncomfortable fact that industrial civilization itself has become the principal driver of global climate", in other words here, as in innumerable articles and reports, the claim is we are in control. Us and our impact, the things we do, primarily CO2 emissions are in the driving seat of global climate.

The whole AGW premise rests on CO2 being the over-riding factor, CO2 and it's greenhouse effect is, has and will continue to influence climate in a way never before known, that it will win over each and every natural climate driver. It isn't, hasn't and won't. Yes, it has an effect but not a controlling one. The biggest impact we apparently face, according to the IPCC is positive feedback and tipping points; primarily that the increased temps will lead to increased ocean temps, forcing more evaporation which creates more clouds thus preventing heat being radiated away out of the atmosphere - we get warmer and warmer but no knows how much warmer.

This premise is fundamentally flawed; Roy Spencer made empirical observations last year which concluded, the opposite is happening, the increase in clouds are actually Cirrus clouds which reflect sunlight and thus cooling, the expected positive feedback and future tipping point has been shown to be incorrect. When I raised this point before it was argued that Spencer was a lone voice, that there was no consensus, no other studies had backed his evidence up but now the NASA Aqua satellite has confirmed his empirical observations.

The NATURAL impact of increased ocean and atmospheric temperatures is an in-built response which results in cooling - a counter balance which has existed since time immemorial. How else have we had CO2 levels of vast proportion compared to today's level without the planet boiling away?

Should I be ashamed? Am I throwing a spanner in the works?

Essan; yes we have an effect, I've never said otherwise but the assertion that CO2 governs everything is (again IMO) utterly absurd. Hansen still adheres to the idea that emissions and their reduction is THE most important thing, that CO2 emissions over-ride everything else. I believe it to be a dangerous perception.

It is the same perception which has led to the explosion in bio fuels, no matter that they actually cause more harm than good, no matter that we are losing vast tracts of rainforest to grow them, no matter that desperately needed agricultural land is being taken away from food production to produce bio fuels. Hey, what does that it matter that continents who struggle to produce enough food already, will have to bear the burden, so long as we get to feel better about driving when we could walk.

It's the same thought pattern which concludes China should be forced to reduce emissions when it is our consumption of cheaply produced goods which fuels their manufacturing. We can reduce our carbon footprint very simply, get other countries to make the stuff for us but we'll be the god boys and they'll be the baddies. How does that work on the grand scheme of things, doesn't make sense to me.

[Thundery wintry showers]

The only legitimate cause for complaint I see with that article is with the use of the word "fact" re. humans being the main driving force- maybe "high probability" or something along those lines would be more accurate. As for the CO2-climate relationship, yes, in the past CO2 has not always been a major climate driver, but we never had the planet's population extracting vast reserves of CO2 and pumping them out into the atmosphere. Indeed the CO2-temperature relationship may well be a positive feedback mechanism, more temperature encourages more CO2 (release from oceans etc) which in turn encourages a rise in temperature. That kind of thing.

In the past we've always had other natural climate mechanisms that came into play to help stabilise the climate, the concern is that humans may be adding to the climate forcings and thus disrupting the planet's equilibrium.

The increase in cirrus clouds coinciding with mass CO2 emissions doesn't prove that CO2 emissions cause cirrus clouds to increase, it could easily be, at least partly, a consequence of increased aircraft activity and thus increased contrails.

I agree that CO2 shouldn't govern our policies- I have increasingly come around to the thinking that sustainability has to be the main focus, at a global as well as regional scale. Unfortunately many people who dismiss AGW prefer to take the line that we should just keep things as they are, and the latter line is often, in itself, a reason for dismissing AGW. (Before anyone takes this personally, note "many", not "all")

[Chris Knight]

No, it isn't CO₂.

Carbon dioxide measured at ground stations is rising, and it is due to anthropogenic fossil fuel use, but not industrialisation.

The carbon sinks are as efficient as they always have been in an interglacial period. Daily urban CO₂ levels of up to 800ppm vanish on a daily basis - due to local sinks. Pure physics gives the answer - increase the partial pressure of a soluble gas in the atmosphere, and it dissolves in the omnipresent water - atmospheric, geospheric, hydrospheric, cryospheric, biospheric - it does not matter where the water exists, carbon dioxide will dissolve in it, and the biospheric, hydrospheric and geospheric components will assimilate it in due course to produce biomass and carbonates. 380ppm of CO₂ is far less than optimal for photosynthetic carbon assimilation.

One notable deception is that the Mauna Loa, and all other global CO₂ measurements are made on dry air, and there is no corresponding record of the water vapour content of the sampled air - which overestimates the ppm of the carbon dioxide - by an unknown amount, unless the data is released.

The atmospheric CO₂ rise over the last 60 years is solely due to aircraft emissions, as is the increase in cirrus clouds due to contrails. Water vapour and CO₂ from burnt aviation fuel at higher and upper levels in the troposphere have no natural sink - these have to diffuse into the lower atmosphere before they can be assimilated by natural processes. Unsurprisingly, over the last 50 years, the carbon dioxide measured has been increasing at an exponential rate - as has air transport.

[Iceberg]

The atmospheric CO₂ rise over the last 60 years is solely due to aircraft emissions, as is the increase in cirrus clouds due to contrails. Water vapour and CO₂ from burnt aviation fuel at higher and upper levels in the troposphere have no natural sink - these have to diffuse into the lower atmosphere before they can be assimilated by natural processes. Unsurprisingly, over the last 50 years, the carbon dioxide measured has been increasing at an exponential rate - as has air transport.

No your very wrong Chris, looking at the isotopic signature of the CO2 shows that it is very very well mixed and very very little of it is from aviation fuel.

[Chris Knight]

No your very wrong Chris, looking at the isotopic signature of the CO2 shows that it is very very well mixed and very very little of it is from aviation fuel.

Where do you think the isotopic mix of the combustion products of aviation fuel comes from? Fossil fuel. When they are measured at ground stations, they have also mixed with biospheric CO₂. Industrial CO2 is also derived from fossil fuel, and does not reach the CO₂ monitoring stations at Mauna Loa, or any of the carefully selected stations far from urban/industrial CO₂. The increase is solely aviation generated - but is a minute proportion of the biospheric production. It is, of course, steadily increasing.

Edited April 13, 2008 by Chris Knight

[jethro]

Evening all..

A few points from various folk, CO2 causing Cirrus clouds...think there maybe some confusion here, the increased CO2 doesn't cause them, higher temperatures both atmospheric and ocean are the cause. It was presumed the extra heat would cause more evaporation, leading to more heat trapping clouds but what actually happens is the reverse. The assumed positive feedback used in the models and the IPCC projections are not happening in reality, the reverse, a negative feedback is happening instead. In other words, those natural climate mechanisms are alive and well and kicking into action.

I think there's a popular conception that because we are the cause of the increased emissions then there must be something special about them, or the rapidity of the rise is dangerous, the Earth won't cope, can't cope. I've thought long and hard on this and I just don't get it. Am I being incredibly dense? When you think about it, the CO2 we're releasing was originally captured from the atmosphere; it's simply going back from whence it came. It's not a noxious gas, it's not a man-made addition which doesn't occur in nature, there's nowt special about it. Yes, there's more of it about than there would be if it had remained buried, yes, we've released lots over a short space of time but does that mean the Earth won't cope? Mother Nature periodically throws vast amounts into the atmosphere in incredibly short spaces of time, but there's no evidence to suggest it changes climate dramatically or that the balance is not restored by in-built mechanisms. Large volcanic eruptions disrupt climate short term but that's caused by sulphur and debris blocking out sunlight, but where's the evidence that vast amounts of CO2 emitted along with the blast cause long term disruption?

Contrails... not a clue, don't know anywhere near enough to be able to comment. The only thing I will say is, I would presume the impact to be most noticeable where there is most traffic. The Spencer study on Cirrus clouds focused on the Tropics, I'm not aware this is a particularly busy area, flight path wise so I can't see how this would be the cause there. Perhaps the Aqua satellite will shed some light on this area; it should be fairly easy to discern patterns over areas such as New York and London.

[Thundery wintry showers]

Some decent points in that post, although I think the scientists who think that Earth cannot cope with the human-induced forcings are very much in the minority. Even if we do get catastrophic short-term climate change, the earth will probably correct itself over the following centuries. The concern is that humans are pumping out so much over such a short space of time, that the climate may change at such a rate that humans (and various other species) may struggle to cope with it.

[Iceberg]

Where do you think the isotopic mix of the combustion products of aviation fuel comes from? Fossil fuel. When they are measured at ground stations, they have also mixed with biospheric CO₂. Industrial CO2 is also derived from fossil fuel, and does not reach the CO₂ monitoring stations at Mauna Loa, or any of the carefully selected stations far from urban/industrial CO₂. The increase is solely aviation generated - but is a minute proportion of the biospheric production. It is, of course, steadily increasing.

Chris,

see the attached link re mixing of CO2 in the atmosphere.

http://cio.eldoc.ub.rug.nl/FILES/root/2002...lusBRamonet.pdf

Scientists can now differentiate between different types of Fossil fuel burnt Carbon isotopes, i.e wood burnt, gas burnt etc.

The height of Mauna Loa is seen to contain many of the industrial category isotopes.

I say again the measuring of the increase of CO2 at remote areas is the only way of ironing out the environment specific CO2 changes. It is well mixed as clearly evident and is the seen increase is not made up predominantly by Aircraft emissions.

[laserguy]

Let's for a moment forget any implications of a link between our CO2 and climate and consider the results of it's curtailment,as in this:

http://www.scoop.co.nz/stories/PO0804/S00187.htm

Thoughts,anyone?

[bluecon]

Some decent points in that post, although I think the scientists who think that Earth cannot cope with the human-induced forcings are very much in the minority.

The argument that a majority or consensus of scientist agree on something proves nothing. The consensus of science has been wrong throughout history innumerable times. Of course many of the great scientific advancements are a result of a scientists that did not agree with the consensus of science.

http://www.scoop.co.nz/stories/PO0804/S00187.htm

Thoughts,anyone?

All the evidence points at a slight cooling that appears to be increasing in scope in parallel to the cooling Sun, yet the AGW crowd will defend their position with know thought of actually accepting the physical evidence.

The game is now fought through controlling the press and manipulating the evidence to suit the theory. It is really a purely political fight at this point and embarassing for the worlds scientific community.

[biffvernon]

The consensus of science has been wrong throughout history innumerable times.

Erm...could you give an example or two? Not from ancient 'science' but from modern, 20th century, peer-reviewed science-as-we now-know-it.

No other area of science has been so thoroughly studied by so many scientists involving so many disciplines, arriving at the consensus that global warming is real is mostly of human making and is a serious threat to human affairs.

[jethro]

No other area of science has been so thoroughly studied by so many scientists involving so many disciplines, arriving at the consensus that global warming is real is mostly of human making and is a serious threat to human affairs.

Slightly grandiose claim there mate.

Despite the IPCC claims, despite all the media hoohah; science never has been based on consensus. It's been based on hypothesis and theories being tested and measured along side empirical evidence in order to confirm, or disprove the ideas. When empirical observation questions the theory, it is the theory which changes, not the other way around.

Put simply, the predictions made by the IPCC, based on their theory, are not stacking up in reality. Their predictions for warming rely heavily upon positive feedback - even they don't claim CO2 alone can cause that much warming, without positive feedback there can be no excessive warming, no matter if one or a thousand and one scientists, say otherwise. If it aint happening, it aint happening, consensus or no consensus.

Can someone please explain just what these claimed serious threats to mankind are?

[bluecon]

Erm...could you give an example or two? Not from ancient 'science' but from modern, 20th century, peer-reviewed science-as-we now-know-it.

No other area of science has been so thoroughly studied by so many scientists involving so many disciplines, arriving at the consensus that global warming is real is mostly of human making and is a serious threat to human affairs.

One of the very best ones is the 2 bicycle mechanics figureing out powered fly when all the scientists were wrong, or Wegner and plate tectonics where the scientific community ridiculed the man. Or recently how the consensus of scientist fought tooth and nail to discount the idea that man was in North and South America long before the end of the last Ice Age, and for the consensus of scientists to ultimately be proven wrong. There are untold other examples.

http://www.ucmp.berkeley.edu/history/wegener.html

Can someone please explain just what these claimed serious threats to mankind are?

Mankind has thrived in the warm spells and suffered through the cold. GW is not a bad thing.

Edited April 14, 2008 by bluecon

[Thundery wintry showers]

The argument that a majority or consensus of scientist agree on something proves nothing. The consensus of science has been wrong throughout history innumerable times. Of course many of the great scientific advancements are a result of a scientists that did not agree with the consensus of science.

Quite right, but the irony of the comment is that it's referring to my statement that most scientists don't believe that the earth's climate system couldn't cope with AGW.

If the scientists are wrong about that (which they might be, just as with anything that isn't completely certain), then we really are in deep trouble.

Mankind has thrived in the warm spells and suffered through the cold. GW is not a bad thing.

Just an additional point here- has mankind thrived in warm spells that were upwards of 1-2C warmer than the present climate? I don't think so. Some evidence (controversial and disputed) suggests that the climate has been 1-2C warmer in the past while humans were about, at least over certain regions of the globe, but no more than that.