Monday
Sep052011
by 
Bishop Hill
Bishop Hill Santer says
Sep 5, 2011 Climate: Models Santer et al have a new paper out on trends in the tropospheric temperature.
Because of the pronounced effect of interannual noise on decadal trends, a multi-model ensemble of anthropogenically-forced simulations displays many 10-year periods with little warming. A single decade of observational TLT data is therefore inadequate for identifying a slowly evolving anthropogenic warming signal. Our results show that temperature records of at least 17 years in length are required for identifying human effects on global-mean tropospheric temperature.
Please keep comments to the subject matter of the paper.
Reader Comments (163)
lapogus
Once again, you are waving the paleoclimate record at me without apparently understanding that it does not in any way support the case that CO2 will not cause significant temperature rise.
Dismissing 30-year climatologies as useless is misguided and more to the point, merely a rhetorical - not scientific - device to support your position. The 30 year climatology is the standard time-series minimum considered for formal evaluations of climate change. Why? Because it is just long enough to capture significant trends (ie something more than inter-decadal variation).
I still fail to see why a set of historical records is proof of CO2's inability to cause significant climate change. The problem is in the here and now (and the future). Not a couple of centuries ago.
You are stuck in a muddle of half-understood factoids and straight-up fallacies. Only you can fix this.
geronimo
This is to ignore the huge body of work that underpins modern calculations of how much energy will accumulate in the climate system as levels of atmospheric CO2 increase. Can I simply invite you to do some desperately-needed reading. You can start here.
You are overstating the case. CO2 is responsible for decreasing the outgoing radiative flux from the surface by about 9%, compared to about a 25% decrease imposed by water vapour (after Ramanathan & Coakley (1978) )
Kiehl & Trenberth (1997) calculate the upward longwave radiation as 390W/m^2 at the surface and 265W/m^2 at the TOA (clear sky) and 390W/m^2 surface vs 235W/m^2 TOA (cloudy sky).
For the relative contributions of various atmospheric absorbers to DLR they find:
Clear Sky
Water vapor contributes 75W/m2 or 60% of the total
CO2 contributes 32W/m2 or 26% of the total
Cloudy Sky
Water vapor contributes 51W/m2 or 59% of the total
CO2 contributes 24W/m2 or 28% of the total
If you genuinely believe that globally, a warming and probably increasingly unstable climate including permanently altered rainfall patterns will have a net positive effect on agriculture, well, fine.
http://www.bishop-hill.net/blog/2011/9/5/santer-says.html?lastPage=true#comment14991785
BBD - there, you wrote it again. "Significant climate change". Every time you write this I put up a link to Nik's graph showing the historical datasets and ask you to show me or point out the 'significant' rise in temperatures in the late 20th Century. I am still waiting for an answer, because you always dodgy the question. Half a degree is nothing in 50 years, given the natural variation of the planet's extremely complex and chaotic climate system. The top six feet of the planet's oceans store more heat energy that the entire atmosphere. We know so little about ocean circulation patterns and cycles, cloud cover percentages over the tropics and mid latitudes and the corresponding insolation rates, that the late 20th C rise in temperature could just be a mix of noise and lag from a warm period in the 19th or possibly before that.
Your assertion that "it must be CO2 because we can't think of anything else" is desperation science at best. Only you can fix this.
lapogus
Unreliable long term historical temperature records do not prove anything. If we treat temperature data from 1900 as just about safe to use, then late C20th warming is highly significant within the context of the period.
Increase in T needs energy to drive it. Our chaotic climate system is not internally powered. So the range of variation it is capable of is limited unless externally forced.
What you term 'natural variation' does not answer the fundamental question: why is more energy accumulating in the climate system now?
Pointing to energetically driven paleoclimate change actually begs this question.
Milankovitch forcing and a high climate sensitivity are required to explain glacial terminations. There is an energetic explanation. This is not internally driven chaotic variation. Nor was the Holocene Thermal Maximum. This should worry you, not make you feel more secure in your beliefs.
Above all, you need to explain why everything we know, including decades of papers calculating the effect on RF at the surface through increasing CO2 is wrong. 'Desperation science' as you call it. Yet much of it dates from long before the current politicisation of the field.
This is the intellectual litmus test: do you believe that so massive a collective error in physical science could go undetected for so long?
Or do you believe that everyone knows it's all guff, but the activists have completely hijacked the field?
In short, can you accept a reality complex enough to include both scientifically sound evidence supporting AGW and bad work like MBH98/99? Do you not see that the misguided PR use of same by the IPCC TAR and others has trapped them into an unending defense of the indefensible? Can you see that this same mistake was made by people trying as hard as humanly possible to raise awareness of what is really happening? They just screwed up.
The core problem here is that you have not checked the other side of the story. But if you can admit the possibility that you may have been misinformed, see my response to geronimo above for a link to a good basic primer on CO2.
I reiterate: you have been badly misled. The cure is an open mind and plenty of reading. Only you can fix this.
BBD - FYI I went along with AGW for nearly 20 years - mainly because I had a good knowledge of physics, understood the extra forcing due to CO2, and believed in the precautionary principal (and I still do believe in the PP). The fact that the majority of winters in the 1990s were mild, and the Arctic ice and majority of glaciers were in retreat, also convinced me something was up. So don't accuse me of not having an open mind, or not having checked the other side of the story. I have, and I have found it lacking, to say the least. From reading a local history book I find that there was a very similar run of mild winters in the 1930s; the Arctic sea ice went through a similarly dramatic retreats in the 1870s and 1920s; and it is clear that many glaciers have actually been in retreat since the early 1800's, long before CO2 emissions became significant. Meanwhile we are having much colder winters again, just like we did in the late 70s and early 80s, and recent summers have been illusory at best. You may think this is all just short term local/parochial weather, but it seems to me that the anecdotal observations from Europe, Asia, north and south America and the Antipodes are beginning to suggest a consistent pattern of cooling in both northern and southern hemispheres. IRRC the latest ocean data appears to bear this out. But let's not have any more real world observations spoil the CO2 thesis, SB11 is probably enough for the team to have to contend with at the moment.
As has been pointed out before, a 1 or 2 % change in cloud cover over the tropics and mid latitudes, and correspondingly increased insolation can easily explain where the addition energy input has come from, and that is before addition energy from the oceans' long lag times are considered. You evidently disagree with this but can you be certain that the cloud cover data is accurate and has not varied for even the last 100 years, when we have only had satellites for 30-40 years?
All you have since 1950 is half a degree rise, of which probably half of that I accept could be due to increased CO2. But even if it is 100% due to CO2, so what? The likelihood is that negative feedbacks will then dominate (if they haven't started to already), and if they don't the worst case scenario is that we prolong the Holocene a little, which considering where I am now was under a 1km of ice 13k years ago this is a very good thing in my book (and just about everyone else in the northern hemisphere - by far most of the world's population). And even for the minority who may face 'climate disruption', through for example changed rainfall patterns, adaption will be much cheaper and easier than futile mitigation measures.
BTW - I am astonished that you have now declared all 8 historical datasets on Nik's graph as unreliable. Six months ago when I posted the graph for some context you said that I was right. Six weeks ago you then suggested that it was only the early pre-1700 CET data which was dubious. Now it is all of them, from pre-1900? I suppose I should get used to you moving the goalposts by now.
lapogus
Did you come across Evans & Puckrin (2006)? Emphasis added:
I understand this:
But I also need to understand why the obvious explanation (CO2) is set aside. It's as if as soon as natural variation is introduced, the laws of physics change and CO2 forcing just... isn't there.
This worries me.
I thought the 'standard' minimum significant period in climatology was 30 years.
BBD, you say “But I also need to understand why the obvious explanation (CO2) is set aside. It's as if as soon as natural variation is introduced, the laws of physics change and CO2 forcing just... isn't there.”
Well, if you’re sure that the margin for error/uncertainty is so small that it has to be CO2, then you need to consider the consequences in terms of future climate change and ask yourself just how alarming/scary this really is and, more importantly, what’s to be done to avoid it.
Unlike other areas of science (e.g. string theory) where the consequences are rather disconnected with ordinary people’s lives, CAGW theory would appear to have major consequences and so demand drastic action (e.g. decarbonisation of the world economy and, most likely, the ‘temporary suspension’ of the democratic process in order to do this). Most sensible people would therefore want to be extremely certain of the evidence upon which to draw such far reaching conclusions and so the question to you is: just how certain are you of the data (errors, uncertainty, completeness, authenticity, etc.) and the methods (e.g. theory and models) involved?
I assume that may sceptics like myself would answer “very uncertain” and await better measurements – and, more importantly, some sort of unambiguous prediction that is verifiable against empirical/real-world data – before making judgement.
So, given this context, the fact that you seem to have now convinced yourself of the certainty of CAGW based upon recent papers by Hanson and other members of the ‘Team’ leaves me with only one comment… this worries me!
Dave Salt
It wasn't Hansen's work in particular - there were many things, and the transition from lukewarmer to orthodoxy took six months (although I knew in my heart of hearts a while back that I had sodded this up).
The problem with your position is that it is logically flawed: the climate is too complex and unpredictable for these 'unambiguous predictions' you want to verify against observations. However, there are a couple of things to go on - the rise in GAT and the intensification of the hydrological cycle were 'predicted' long ago. Polar amplification was expected too.
But yes, we edge towards post-normal science. All you can do is weigh as much of the evidence as you can and take the prejudicial blinkers off. And burn them.
BBD, am truly sorry to hear your conclusions because, after everything you have posted, I still fail to see the 'evidence' as even suggestive let alone conclusive because, fundamentally, the S/N is just too poor.
That you can now consider post-normal science as the only rational way of approaching this subject is rather disappointing and suggests that your thinking has as much to do with politics as science. I note that you made no mention about consequences, so can only assume that you now reluctantly favor drastic action but are reluctant to discuss it here.
Dave Salt
If you find the current state of knowledge insufficient to persuade you, then you must follow your own judgement.
As for the 'drastic action', which you define as 'decarbonisation of the world economy and, most likely, the ‘temporary suspension’ of the democratic process in order to do this', then no, that's going much too far.
Decarbonisation of electricity generation and a shift away from FFs to electricity hardly requires the suspension of democracy.
It will require some better thinking about energy policy than we have seen to date. The misrepresentation of the realistic potential of wind and solar is a serious problem. The turbulent anti-nuclear lobby is another. Domestic energy efficiency offers much potential, but will be politically unrealistic if it looks like - or worse, feels like - rationing.
As with GM, the greens are very much the problem, not the solution.
Unclear above. I should have said: 'the exaggeration of the realistic potential of wind and solar'.
Recall it was Hansen et al 2005 that used years of "robust" data from OHC for which Hansen said was "the smoking gun" for AGW, and IPCC AR4 was more than happy to cite that paper.