A new study indicates that there may still exist some as of yet unidentified positive feedbacks in the climate system that could make future warming greater than previously estimated.
A reconstruction of the Earth’s climatic history during a key hot period 55 million years ago has highlighted a yawning gap in our understanding: this period’s rise in carbon dioxide accounts for just half of its warming. Some as-yet-unidentified climate feedbacks could be at work, the scientists behind the research conclude.
The era under scrutiny is the Palaeocene-Eocene Thermal Maximum (PETM). Paleoclimatologists believe that the PETM could mimic our own future climate, because it’s thought to have kicked off with a pulse of carbon dioxide roughly equivalent to what humans are currently pumping out by burning fossil fuels…
According to the IPCC’s best guess at climate sensitivity, that 70% rise should have pushed up global temperatures 3.5 degrees Celsius at most. Other proxy records indicate, though, that temperatures soared by 5 to 9 degrees. In other words, the consensus climate sensitivity – the value, devilishly hard to pin down, for how much warming will result from a given greenhouse gas increase – doesn’t seem to be holding.
This is yet another example of the conservative nature of the IPCC reports. But that is to be expected from a consensus document.
And this isn’t the only research indicating the the IPCC’s estimate of climate sensitivity might be low.
UPDATE: It looks like deniers are trumpeting this study, because it highlights that the current crop of models are uncertain. Unfortunately for them the uncertainty highlighted by this study is in the wrong direction, it indicates that the models may be underestimating the expected warming, and as I pointed out in my post this isn’t even a surprising revelation.
The IPCC estimate of climate sensitivity is commonly called the Charney sensitivity; it excludes a bunch of long term feedbacks. This new study (along with other studies, such as Hansen’s 350 ppm paper) provide evidence that the Charney estimate of sensitivity is low. How low? I don’t think we can answer that yet with much confidence, but as was pointed out on RealClimate when the Hansen paper was making the rounds:
However, even with the (substantial) uncertainties in the calculations and underlying assumptions, the conclusion that the Earth System sensitivity [which includes these slow feedbacks] is greater than the Charney sensitivity [which doesn’t] is probably robust. And that is a concern for any policy based on a stabilization scenario significantly above where we are now.
So basically this study says that the models may be underestimating the expected warming. And yet deniers are excited by it? Obviously they didn’t read/understand the study. And they actually have the audacity to complain when they are not taken seriously!
It looks like a simple alternative explanation has escaped your attention (and attention of authors of this study). In fact they found another evidence that CO2 does not define anything much in the global climate. Similarly, ice core records also show that CO2 concentration lags temperatures, and therefore is unlikely to be the driver of climate. Or another recent fact of counter-trends in CO2 and global temperatures from instrumental records of 21st century. Or another fact that climate modelers have to fudge their models with unfounded “positive feedbacks” in attempt to fit their results onto modern climate history. Obviously, if CO2 does not affect climate in any serious way, attempts to patch the theory with more sophisticated one-sided “positive feedbacks” will look more and more ridiculous.
Actually they found no such thing. No where in the study is that claimed, because the data simply doesn’t back it up. Nothing in the paper speaks to the radiative properties of CO2. All the paper is discussing is that we currently do not have a good explanation for the PETM, and this suggests that we may be missing some feedbacks. And as I pointed out in the original post this has already been suggested by other studies.
This has been addressed here, here, here, here, and here.
Again I have already addressed this point. See here.
Unfounded? The most important feedback (at least of the quick feedbacks) is water vapour. As the atmosphere warms more water evaporates from the oceans and ends up in the atmosphere. And as deniers like to remind us, water vapour is the most important GHG. This means that if the atmosphere warms a little, the water vapour content will increase and warm up the atmosphere even more. Thus a positive feedback. And yes there is a mountain of evidence to back it up. Other feedbacks are even easier to back up. Arctic sea ice has a high albedo, open ocean water has a lower albedo. When the sea ice melts more of the sun’s energy is absorbed by the ocean thus warming it up further. That is not unfounded. Of course other feedbacks are more controversial, but that doesn’t mean they are unfounded.
In fact as this (and many other studies have shown) the paleoclimate cannot be explained without feedbacks. As Wallace Broecker who famously said: “The paleoclimate record shouts out to us that, far from being self-stabilizing, the Earth’s climate system is an ornery beast which overreacts even to small nudges.” Those overreactions are because of feedbacks.
So says a random blog commenter, yet the vast majority of scientists, the IPCC the National Academies of Science from Australia, Belgium, Brazil, Canada, the Caribbean, China, France, Germany, India, Indonesia, Ireland, Italy, Japan, Malaysia, Mexico, New Zealand, Russia, South Africa, Sweden, the United Kingdom and the USA, the American Meteorological Society, American Geophysical Union, the American Association for the Advancement of Science, the Geological Society of London, the Geological Society of America, the Canadian Meteorological and Oceanographic Society, and thousands of peer-reviewed journals say otherwise.
You are making what I would call and extraordinary claim (claiming mainstream science is incorrect). That requires extraordinary evidence to back it up, yet you have presented nothing. You are going to have to do a lot better.
That has got to be about as anti-science as one can get. Theories are constantly tinkered with (patched if you will) as new data comes in and our understanding increases. They are never set in stone. And it is precisely this property of science that makes it so valuable and important.
Please do not repeat points that have already been thoroughly debunked
I think you did not get the point. It does not matter what the particular authors did claim or did not. I am telling you that there is an alternative explanation of their findings, which correlates well with ice records and modern records, 1940-1970 range, and post-1998 range. The missing possibility is that CO2 does not affect global climate in a serious way, and climatology has to invent more and more “feedbacks” to explain data.
The juvenile “exlanations” of CO2 “rising together” like this one are laughable at best. This “explanation” of mutual feedback from CO2 to temperatures and back (a-la Lotka-Volterra) has at least tree problems, (1) small orbit “wobbling” does not change average global insolation, so triggering of global deglaciation must be explained with additional unfounded speculations; (2) if the rise of CO2 amplifies temperatures in a positive feedback loop, what stops this process (keeping in mind previous point)?; and (3) why this process is so asymmetric in time, rapid deglaciations, and slow sliding into ice ages.
Constant “tinkering” with theory is good when it converges to a certain mechanism. In this case the theory diverges more with this findings. Patching the “standard GH effect theory” with more “undiscovered feedbacks” is the same thing as an attempt to add more whales to the other three who support the flat disk of Earth.
The problem with your alternative explanation is that it is contradicted by a large mountain of evidence. CO2’s radiative properties are well known; they cannot jut be ignored.
There is a good reason why the authors of this study (or those who peer-reviewed it) didn’t mention your alternative explanation.
As for what triggered past climate change, obviously there are several unanswered questions, but that does not in any way speak to what is triggering THIS episode of climate change. It simply isn’t logical to assume that the current change in climate cannot be caused by CO2 because other past changes in climate weren’t.
That is like a defence lawyer arguing that his client cannot be the killer, because there have been killings that the client obviously did not commit. It just makes no sense.
As for your questions, they are valid, and as far as I know there aren’t any non-controversial answers (remember there is still MUCH we don’t know about the paleoclimate), but it doesn’t logically follow to conclude that CO2 has no effect on climate as you have done. Large natural variability in the earths climate doesn’t disprove AGW.
Remember the AGW was predicted (with a high level of confidence) at a time when most of the paleoclimate record was still a mystery.
I guess you didn’t reed my links above. Please read this, if you wish to continue this discussion.
Also if we are going to continue this discussion I think you need to answer the following questions:
My Answers can be found here.
You want to hear my answers to your “tough” rhetorical questions, here they are:
(1) Why don’t I accept the conclusions arrived at by the overwhelming majority of scientists?
This is an ill-posed question. First, climatology constitutes minority of sciences. All scientists whom I personally know (mostly in physics or engineering) are in complete rejection of the anthropogenic CO2 part. Anyone who knows a thing or two about computer modeling of continuous turbulent media considers overconfidence of climate modelers as an insult to the spirit of science. Second, overwhelming majority of climate scientists did not arrive to the “A” part of GW. Only few people invented the “A” part, under leadership of James Hansen. There are only few people. However, the overwhelming majority of climate scientists are just taking this great opportunity of lifetime to support their own research, which could be legitimate. They use this AGW scare mongering as umbrella. I would do (and did in the past) the same thing. It is business, you need to fund your own research, and the choice to ride on the wave of AGW scare seems most effective, especially if you use correct scientific language “if” and “likely” in publications.
(2) Why do I think the vast majority of scientists are wrong?
I do not think that “vast majority” is wrong. I just think that few short-sighted and semi-educated leaders are wrong. For the rest of them, see above. The magnitude of “radiative forcing” is a purely computational construction. It relies upon a _three-step_ chain of assumptions about mechanism of imbalance across all atmospheric layers, “stratospheric adjustment”, “zero-surface-temperature-change”, “equilibrium climate response”. Each of these steps is highly speculative and dubious, and it could be easy to go wrong given non-smooth functional behavior of gas absorption-emission spectrum.
(3) What would change my mind and make me accept anthropogenic global warming and why have I chosen those criteria?
It is hard to accept anthropogenic case of climate variations because these variations are known to exist for millions of years without any help from industrial exhausts. I could probably consider anthropogenic effects of aerosols, deforestation and soot deposits, but not from CO2.
Consider a simple example from data. If you believe that Antarctic ice quantitatively preserves concentration of ancient CO2, and dO18 correctly represents global temperature, the Vostok ice cores show a correlation that can be interpolated as 8ppm/K,
These are the observational data, and they apparently include _all_ possible climate feedbacks. Now, if you assume (as IPCC and all AGW acolytes do) that CO2 is the main driver of temperatures, then the modern 375ppm of CO2 should force global temperature to rise for another 13.5K. Thus one would expect today’s global temperature to be 301.5K, which is not true by far. This simple estimate shows that the attribution of today’s warming to CO2 emissions is seriously flawed.
Thanks for your answers. But you kind of missed the point of questions 1 and 2, though perhaps I wasn’t as clear as I could have been.
Obviously we don’t really care about all scientists in general. Frankly what a veterinary scientist has to say about AGW is not relevant. The same goes for many other scientific disciplines. They just aren’t relevant to AGW. I though it was pretty obvious from the question and my answers that I was referring to the scientists with relevant expertise. And in that area they certainly does exist an overwhelming support for AGW (see here, and the list of scientific societies above).
As for the scientists you personally know, if they think the theory is flawed, why don’t they subject their ideas the the rigours of peer-review. Why don’t they publish some papers demonstrating why AGW is not real. Were they do disprove it they would instantly become household names and would be set for life (in terms of salary and funding for their research). The fact that they haven’t done so (if they have please prove me wrong ans send me the link), leads me to believe their ideas wont stand up to scrutiny.
And what denier claims wouldn’t be complete without the usual models can’t be trusted talking point. Save it. A quick read of the literature shows that models have and are heavily scrutinized. How do you explain their accuracy in hind casting the last century of climate?
That is a bold claim. care to back it up? Or am I supposed to take your word, that a small cabal of scientist lead by James Hansen, has successfully duped the worlds scientific societies (see list above) and governments (they sign off on each and every IPCC report). And of course that would require me to ignore the science that was done BEFORE Hansen, starting with John Tyndall in the 1850s. Frankly that is too much of a conspiracy for me to believe without very compelling evidence.
And please spare me the whole, they only do it for money argument. It doesn’t hold much water. First, there are effective safeguards against this sort of thing in the academic world (without them science would be much less useful), secondly anyone who was able to debunk climate change would instantly be awash in money (thanks to Exxon et al.)for themselves and to fund any further research they wished to conduct. Just look at what Lindzen Singer Ball and other make from their denial, and their ideas have all been debunked (or in the case with Lindzen lost prominence due to a lack of evidence to support it). And given the last US administration’s hostile attitudes towards AGW it makes even less sense. Wouldn’t skeptical scientists have come out of the woodwork during the Bush years? Where are they?
And this doesn’t even begin to take into account the fame that anyone who debunked global warming would receive.
The whole system is highly incentively to prove the established knowledge wrong. That is what continuously pushes science forward.
This sums it up nicely.
As for question 3, I am very puzzled by your answer.
First you sate that:
True, the climate does change due to natural forcings, but that doesn’t speak to the fact that human GHG emissions might also be a forcing. Natural, and anthropogenic climate change are not mutually exclusive.
Then you sate
That statement puzzles me. Of the forcings you listed, CO2 is probably the most understood. It goes back to John Tyndall in the 1850s, who first measured the radiate properties of CO2. As far as I know there isn’t any serious challenge the CO2 forcing. People like Lindzen instead argue that negative feedbacks will negate any future warming (the data doesn’t support this), and Fred ‘Tobbaco is healthy” Singer recently resigned as an editor of Enviromental Geology because they published a paper arguing something similar.
That fact that you accept climate forcing that are not yet that well understood (especially deforestation and soot deposits), while not accepting the simpler and better understood CO2 forcing is odd indeed.
Spoken like someone who hasn’t bothered to read what the IPCC actually says. The IPCC identifies CO2 as one of many forcings. All it says about CO2 driving climate is that it is driving the current warming trend. It remains unclear what ‘drove’ past climate changes, though CO2 was likely a feedback.
No, this estimate (really just an extrapolation) shows that you have little understanding of the issue. The biggest problem is that you assume a linear relationship. That is probably a poor assumption, especially given what we know about tipping points.
Don’t you think that if such an obvious flaw existed in AGW theory that someone would have published a paper on the subject? I haven’t seen one have you?
But when it comes right down to it you haven’t answered the question. What would change your mind and make you accept anthropogenic global warming and why have you chosen those criteria?
If nothing will change your mind that clearly you aren’t looking at this issue rationally, and I don’t see the point in continuing this discussion.
An interesting paper by Lindzen and Choi:
Climate feedbacks are estimated from fluctuations in the outgoing radiation budget from the latest version of Earth Radiation Budget Experiment (ERBE) nonscanner data. It appears, for the entire tropics, the observed outgoing radiation fluxes increase with the increase in sea surface temperatures (SSTs). The observed behavior of radiation fluxes implies negative feedback processes associated with relatively low climate sensitivity. This is the opposite of the behavior of 11 atmospheric models forced by the same SSTs. Therefore, the models display much higher climate sensitivity than is inferred from ERBE, though it is difficult to pin down such high sensitivities with any precision. Results also show, the feedback in ERBE is mostly from shortwave radiation while the feedback in the models is mostly from longwave radiation. Although such a test does not distinguish the mechanisms, this is important since the inconsistency of climate feedbacks constitutes a very fundamental problem in climate prediction.
I’d say that is good news on the feedback front, but I would caution about getting overly excited. This isn’t the first time Lindzen has proposed a negative feedback, and so far his ideas haven’t really gone very far due to contradictory evidence. That doesn’t automatically discount this proposal but it does make me question it (I am not really qualified to judge this paper on its merits), especially given some of the verifiably wrong stuff Lindzen has been saying of late.
If Lindzen has truly found a negative feedback this paper will gain prominence and be cited a lot by other building on his work. If Lindzen hasn’t really found anything, then either this paper will be refuted, or simply ignored.
Only time will tell how the scientific community responds.
The words of John Mashey are particularly relevant here:
For more read this.