The debate about climate change is a very polarized one.
Understanding the points of view of people who disagree with you is essential to making progress. Even more importantly, you should understand the arguments that summarize the best of the opposite point of view.
Much that is written in the general media is the “polarized view”. So here is a wonderful open letter from a climate scientist that sums up a “skeptical” point of view in a humble way. Emphasis added.
I would add that the view presented is also the point of view of this blog. Standing on the shoulders of giants..
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Date: Mon, 07 Dec 2009 08:28:38 -0700
From: Petr Chylek
To: Climate@lanl.gov, energy@lanl.gov, isr-all@lanl.gov, ees-all@lanl.gov
Dear Climate People:
FYI below is a letter that I sent on Saturday to about 100 top climate research experts including Jim Hansen, Steve Schneider, Phil Jones (UK) and other superstars. Till now I got 14 replies which are about 50/50 between supporting of what I said and defense of the IPCC process.
Greetings,
Petr
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Open Letter to the Climate Research Community
I am sure that most of you are aware of the incident that took place recently at the University of East Anglia’s Climatic Research Unit (CRU). The identity of the whistle-blower or hacker is still not known.
The selected release of emails contains correspondence between CRU scientists and scientists at other climate research institutions. My own purely technical exchange of emails with CRU director Professor Phil Jones is, as far as I know, not included.
I published my first climate-related paper in 1974 (Chylek and Coakley, Aerosol and Climate, Science 183, 75-77). I was privileged to supervise Ph. D. theses of some exceptional scientists – people like J. Kiehl, V. Ramaswamy and J. Li among others. I have published well over 100 peer-reviewed papers, and I am a Fellow of the American Geophysical Union, the Optical Society of America, and Los Alamos National Laboratory. Within the last few years I was also honored to be included in Wikipedia’s blacklist of “climate skeptics”.
For me, science is the search for truth, the never-ending path towards finding out how things are arranged in this world so that they can work as they do. That search is never finished.
It seems that the climate research community has betrayed that mighty goal in science. They have substituted the search for truth with an attempt at proving one point of view. It seems that some of the most prominent leaders of the climate research community, like prophets of Old Israel, believed that they could see the future of humankind and that the only remaining task was to convince or force all others to accept and follow. They have almost succeeded in that effort.
Yes, there have been cases of misbehavior and direct fraud committed by scientists in other fields: physics, medicine, and biology to name a few. However, it was misbehavior of individuals, not of a considerable part of the scientific community.
Climate research made significant advancements during the last few decades, thanks to your diligent work. This includes the construction of the HadCRUT and NASA GISS datasets documenting the rise of globally averaged temperature during the last century. I do not believe that this work can be affected in any way by the recent email revelations. Thus, the first of the three pillars supporting the hypothesis of manmade global warming seems to be solid.
However, the two other pillars are much more controversial. To blame the current warming on humans, there was a perceived need to “prove” that the current global average temperature is higher than it was at any other time in recent history (the last few thousand years). This task is one of the main topics of the released CRU emails. Some people were so eager to prove this point that it became more important than scientific integrity.
The next step was to show that this “unprecedented high current temperature” has to be a result of the increasing atmospheric concentration of carbon dioxide from the burning of fossil fuels. The fact that the Atmosphere Ocean General Circulation Models are not able to explain the post-1970 temperature increase by natural forcing was interpreted as proof that it was caused by humans. It is more logical to admit that the models are not yet good enough to capture natural climate variability (how much or how little do we understand aerosol and clouds, and ocean circulation?), even though we can all agree that part of the observed post-1970 warming is due to the increase of atmospheric CO2 concentration. Thus, two of the three pillars of the global warming and carbon dioxide paradigm are open to reinvestigation.
The damage has been done. The public trust in climate science has been eroded. At least a part of the IPCC 2007 report has been put in question. We cannot blame it on a few irresponsible individuals. The entire esteemed climate research community has to take responsibility. Yes, there always will be a few deniers and obstructionists.
So what comes next? Let us stop making unjustified claims and exaggerated projections about the future even if the editors of some eminent journals are just waiting to publish them. Let us admit that our understanding of the climate is less perfect than we have tried to make the public believe. Let us drastically modify or temporarily discontinue the IPCC. Let us get back to work.
Let us encourage students to think their own thoughts instead of forcing them to parrot the IPCC conclusions. Let us open the doors of universities, of NCAR, NASA and other research institutions (and funding agencies) to faculty members and researchers who might disagree with the current paradigm of carbon dioxide. Only open discussion and intense searching of all possibilities will let us regain the public’s trust and move forward.
Regards,
Petr Chylek
Why hasn’t anybody else commented on this blistering attack on nearly the entire climate science community? Maybe you could repost it just in case somehow everybody missed it. It would interesting to see the updated feedback that Chylek has received from his climate science peers.
I’m studying your posts and really enjoy the technical approach. One thing I’m looking for is how CO2 infrared radiation has a significant impact on the OHC (which contains 99.9% of the climate energy).
Steve Koch:
Thanks for the comments.
On OHC, the first post is now up – The Real Measure of Global Warming but of course, this isn’t attribution. This is simply measurement.
I’ll think about how to weave Chylek’s great words into another post, perhaps as the series on Models On – and Off – the Catwalk progresses slowly forward.
I very much enjoyed this post. It is nice to find out some of the website proprietor’s positions on a few things.
However, I would have to disagree with Petr (and, by extension, with scienceofdoom) on the first pillar. It appears to me that there is ample evidence that the warming over the past century may have been greatly overstated. If so, then climate science is 0 for 3 on the pillars.
There isn’t a lot to comment about on this post. Dr. Petr Chylek has made a very balanced, honest assessment of what has gone on in climate science. The whole IPCC process is politically engineered to support the idea that human influence is the primary cause of the modest increase in temperatures over the last 150 years. The science has been subverted by the politics.
We’re over a year on and nothing much has changed. The hockey stick guys sure haven’t changed, still keeping the data behind lock and key.
It’s good to see blogs like this striving for truth, whatever it may be.
[…] 110 peer-reviewed papers to his name, including papers co-authored with the great Ramanathan and Petr Chylek, to name just a […]
This is a splendid summary of the state of affairs. Dr. Chylek’s thoughts should be disseminated widely.
Incredibly well executed blog post.
I’m not sure what it is that people find so compelling about this letter. It contains no scientific evidence and its principle point is political, yet, provides no political evidence in support of it. Perhaps he and others think this evidence is self-evident. It’s certainly not to me.
To the extent that the public distrusts climate science, its not because climate scientists have made exaggerated claims in the past. I’m not denying that this has happened, but I question the extent to which this has happened and the public’s awareness of it.
A much more likely explanation of the public’s distrust of climate science is that a group of extremely ideological pundits have been vocal about it for years. They make no good points, either logically nor scientifically, but it persuades the public because these same pundits have persuaded their listeners that their uneducated, scientifically illiterate “common sense” is better than anything the academic “elites” have come up with (who are only motivated by pushing a totalitarian agenda, they say).
I’m reminded of an office mate who went around every day saying “it’s the sun, it’s the sun, you know what I’m saying” until I finally couldn’t take it anymore and commented on why that level of analysis explains nothing, not just about global warming, but any of the myriad conditions which exist on the planet. He finally conceded, but until that moment, he never really thought about it.
I suggest that THAT is the reason the public doesn’t trust climate science.
Ted: This letter doesn’t contain any scientific evidence because the recipients of the letter were intimately familiar with the evidence and controversies.
Chylek wrote:
“However, the two other pillars [supporting the hypothesis of catastrophic anthropogenic climate change] are much more controversial. To blame the current warming on humans, there was a perceived need to “prove” that the current global average temperature is higher than it was at any other time in recent history (the last few thousand years). This task is one of the main topics of the released CRU emails. Some people were so eager to prove this point that it became more important than scientific integrity.
The next step was to show that this “unprecedented high current temperature” has to be a result of the increasing atmospheric concentration of carbon dioxide from the burning of fossil fuels. The fact that the Atmosphere Ocean General Circulation Models are not able to explain the post-1970 temperature increase by natural forcing was interpreted as proof that it was caused by humans. It is more logical to admit that the models are not yet good enough to capture natural climate variability (how much or how little do we understand aerosol and clouds, and ocean circulation?), even though we can all agree that part of the observed post-1970 warming is due to the increase of atmospheric CO2 concentration.”
As a retired PhD scientist who has read widely on both sides of this subject for the past several years, I’d say that Chylek is right on both points. Is that why the public “distrusts climate science” or why public support has diminished (to put it more accurately)? One can speculate endlessly about what accurate factual information “the public” knows and why they believe what they believe. Opinions abound and factual information is scarce. Science is concerned with certain aspects of what we know. Chylek says:
“Let us stop making unjustified claims and exaggerated projections about the future even if the editors of some eminent journals are just waiting to publish them. Let us admit that our understanding of the climate is less perfect than we have tried to make the public believe.”
Will this restore (as Chylek hopes) or further reduce public trust in climate science? Who knows? However, as a scientist, I care about the integrity of science, particularly the information that is being presented to policymakers. In the future, who is going to trust scientists on any subject if we waste trillions on a threat that has been greatly exaggerated for political reasons?
One interesting thing about this letter is what it says about our host, who is forced to spend far too much time dealing with the skeptical pseudoscience spread by your office-mate. However, if you are looking for solid SCIENTIFIC information about climate change, there is no better place to look than our host, someone who recognizes some of the problems with climate science without encouraging the skeptical lunatic fringe. Unfortunately, you won’t find too much material supporting the problems in Chylek’s letter.
Thank you for your thoughtful response. Though I didn’t find much in the letter to sway my thinking one way or another, I will concede that others who are in the field and know all the science may find it compelling.
Personally, I am not a professional scientist but I do have some university training in the sciences. I never adopted a position on AGW because I never took the time to learn anything about it. Recently, I’ve taken an interest in changing that so I’ve been trying to go back an re-learn some of the basics, including things like thermo, physical chemistry and radiative heat transfer in order to have some knowledge to judge things by. In this regard, I’ve found this site invaluable – so yes, absolutely, I appreciate all the time and effort our host has taken.
I do agree that climate scientists should stay away from exaggeration. Its tempting, I imagine, because our society doesn’t pay attention to anything unless its some kind of hyperbolic thinking. One, it seems, needs to shout in order to be heard. But, in the end, it will come back to haunt you. For example, I did a search not too long ago about exaggerated claims made during the ’70’s about global cooling and the pending ice age. And, the skeptics ARE right about that. Those claims were made, by profession scientists and their organizations. I don’t think that it was the dominant belief of most scientists of the time, but there were those who said those things in the name of science. The other scientists, the ones who didn’t hold that position, never really spoke out publicly. So their position isn’t easy to find. The ice age guys are there for all the world to see. For the skeptics to bandy about to the public and say…look, its all a fraud.
Scientists are a diverse group. There are ideals that I would like be applied by every scientist, but it should not surprise anyone that the reality is not like that. Stephen Schneider is an example of scientist, who has written openly on his views on the conflict between the ideals of science and being influential. I accept that he had the right for his views, but I think that he erred. He should have understood that making compromises on the scientific ideals make the science less powerful and less influential in the long run, even if the initial influence may be larger.
A major problem is that the “skeptic” side has taken full advantage of this error and got many to believe that scientists are much less honest than they really are. To get the most objective understanding only a few scientists should be given less weight and most trusted as much as scientists of less controversial fields. In this spirit, I think that Chylek overdoes his argument, but I do admit that it’s unnecessarily difficult to know what to trust and what not.
Pekka: I thought Schneider explained his dilemma very well, but didn’t come up with the right answer. If you want to speak to the public as a scientist, follow scientific ethics and include all of the caveats. If you want to speak like an activist or politician and tell scary stories, explain that you are extremely knowledgeable about the subject, but so concerned that you will be focusing on worst-case scenarios and omitting uncertainty, doubts and caveats. The problem arises when audience and policymakers think they are hearing ethical science and they are getting scary stories.
Reporters and policymakers should question scientists as to whether they are answering questions as an ethical scientist or as a policy advocate.
TedH: There may have been some concern about global cooling at one point, but the alleged problem was never subject to anything like the same scrutiny as global warming. Discounting the threat of global warming because the press publicized the fears of a few scientists about global cooling seems misguided.
The problems Chylek discusses above aren’t directly concerned with catastrophic AGW. Whether or not current temperature exceed the MWP or any earlier period, if climate models are right and equilibrium climate sensitivity is >= 3, temperatures soon will be unprecedented in the last million years and will continue to rise from there. The same is true about whether it was correct for the IPCC to attribute most recent warming to man today; we soon will be – if models are right. Attribution and “unprecedented change” are important for policy advocacy today, not projections about the future.
Pekka
I think you are being rather complacent here.
I probably typify the reaction of a person with a graduate level physics background and a general interest in science developments.
I had only a superficial interest in Climate Science pre-climategate.
My friends, all from a varied scientific background would occasionally discuss ‘global warming’ .
My attitude then would then have been, let the Climate Scientists get on with it.
The media says 97% of all scientists agree with the IPCC and the science is settled.
I trusted that all scientists worked within the guidelines of the scientific method as outlined by Karl Popper.
Climategate showed that my previous views were extremely gullible.
The subsequent enquiries into Climategate were blatant establishment cover ups.
For instance Lord Oxburgh with extensive financial interests in renewable energy was in charge of one.
Like putting the chairman of Imperial Tobacco in charge of a committee to look into the harmful effects of smoking!
What was more disturbing was the attitude of most Climate Scientists to the shocking revelations.
Complacency and defending wrongdoing instead of ruthlessly rooting out those who had departed from the scientific method.
So I decided as a citizen with a science background to take more of an interest
A scare story of climate would get more funding and it’s all in a good cause seemed to be the attitude.
Bertolt Brecht in his play ‘Galileo’ proposed that scientists should have a form of ‘Hippocratic Oath’ which would prohibit such behavior.
Politically I am of the left and I notice the irony of poor people paying for increased fuel and transport costs to combat so called ‘global warming’
Many thousands of old people in Britain die from hypothermia as a direct result of what may turn out to be climate alarmism.
Bryan,
You are an explicit example of what I was writing about. You have accepted fully one interpretation of the story, while that’s really remote of the full story.
A few scientists have shown that they are fallible humans. Perhaps that was a news to you, to me that wasn’t a news.
I’m a great believer in the scientific process, but I have known for decades that the details are often messy. Many people are so disappointed in what has come out, because they had totally unrealistic expectations. Science is very powerful as a process, but individual scientific papers and individual scientists are very often wrong. Scientific results are strong only after bieing confirmed by further independent research.
Bryan,
“Many thousands of old people in Britain die from hypothermia as a direct result of what may turn out to be climate alarmism.”
What specifically do you mean by this particular statement?
RW,
That sentence tells a lot about Bryan (and nothing about climate alarmism).
RW and Pekka
Perhaps you dont live in Britain or dont get much time to read the news.
Hopefully neither of you think that these deaths are a small price worth paying to halt global warming.
Fuel bills are soaring in Britain largely because of Government edict to stop using fossil fuels and instead use renewable sources such as solar panels and windmills.
Fuel taxes and restrictions are regressive i.e. they adversely affect poor people more than rich people.
The reason for this energy policy is that the IPCC say dire consequences will follow unless fossil fuel use is minimised.
Now if Climate Science was open and transparent and climate models were reliable then perhaps there is no alternative.
However Climategate indicated a murky world of interference with peer review and media manipulation.
Perhaps Pekka is right when he says that this kind of thing is quite common in science.
Perhaps I was rather naive in thinking that the rest of Climate Science community would be shocked and would root out such behavior.
Pekka seems quite unconcerned and instead draws conclusions about those who don’t share his complacency.
http://www.dailymail.co.uk/news/article-2100232/Frozen-death-fuel-bills-soar-Hypothermia-cases-elderly-double-years.html
Bryan,
Claiming that those deaths are due to climate alarmism is simply ..
Bryan,
What I mean is that you have no problems in accepting and promoting a wild hypothesis as true while you dismiss very much well justified and valid science. You accept anything when it supports your preferred views and dismiss contrary arguments.
Reading the article that you link does not support at all your claim that climate alarmism is the cause of the deaths. Soaring gas prizes are mentioned, but the reasons of that are not in climate policy but rather in running out of the low cost gas wells of North Sea. (That’s not the only reason, but climate policies are not near to the top.)
Bryan,
I was just asking – that’s all.
Britains energy policy is being directed to solve what might prove to be a non existant problem.
For instance no significant global near surface atmospheric temperature rise for 17 years.
Now if in spite of this there is a sound basis in science then the science should be capable of standing up to scrutiny.
However scrutiny it seems is not welcome.
There would be very little public and scientific opposition to the IPCC proposals if we had a healthy sceptical Climate Science community.
IPCC policy seems to make progress through becoming a ’cause’ that should render it to be above the sceptical approach.
I have asked several people without any reply;
‘what would falsify the significant man made global warming conjecture’
It appears that it is beyond being falsified.
You think that this is a general feature of science and not unusual .
Perhaps I am naive to think that science progresses by falsification from healthy robust questioning as advocated by Feynman.
This are severe consequences in following the present policy
Former mining communities left in unemployed poverty.
Energy intensive industry moved offshore.
In Britain the Green Party opposes Fracking
It seems that any expensive non carbon proposal is passed without scrutiny on the basis of IPCC ‘science’
Public debate is banned from TV outlets the Climategate e-mails show the extent of behind the scenes manipulation of the media.
http://www.telegraph.co.uk/earth/energy/windpower/10122850/True-cost-of-Britains-wind-farm-industry-revealed.html
http://bishophill.squarespace.com/
Bryan,
Any number of things would falsify it. For example, failing to detect any DLR when measurements are made. But if you look and they turn out consistent with the theory, then… the theory stands.
What is the ‘theory’. To say the CAGW supported by the IPCC (i.e. about 3C of warming per CO2 doubling) is a ‘theory’ is really, really stretching it to say the very least. At best it is a weakly tested hypothesis.
Also, measured DLR does not in any way establish or validate the CAGW case. Most agree the fundamental physics supports a strong likelihood of at least some effect, but that’s trivial.
Bryan,
Back radiation is disputed by some. It was just the first thing that came to mind as a way to falsify the CAGW hypothesis. Here is one argument, that says essentially that all back radiation measurements are false.
Click to access Test%20Results%20-%20411-512.pdf
TedH
This would mean that CO2 and H2O would not radiate at all.
Which is not disputed by anyone.
More testing questions would be;
‘would increasing atmospheric CO2 for the next 30 years be compatible with a temperature standstill or even decline?
‘would increasing atmospheric CO2 for the next 300 years be compatible with a temperature standstill or even decline?
At what point would continued support for the IPCC conjecture just seem absurd
TedH,
Here is just a quick list of the many other things the data and evidence is telling us:
1. CO2 lags temperature in the ice core paleo data, and the lag is longer when temperatures are falling. This is exactly the opposite of what would be expected if CO2 was any significant driver of the temperature increases from the glacial to interglacial periods.
2. The relationship between water vapor concentration and temperature is the opposite of what one would expect from positive feedback from water vapor. That is, above the current global average temperature, on average as the water vapor concentration increases more and more, the temperature increases less and less, as illustrated here:
3. The power densities gain ratio of the surface to post albedo solar incident solar radiation is only about 1.6, where net positive feedback of 300% requires a gain ratio of more than 4.8 (at 287K, the surface gains about 385 W/m^2 and about 240 W/m^2 enters from the Sun; 385/240 = 1.6, and +3.3C from a baseline of 287K requires +18 W/m^2 of surface power gain; 18/3.7 = 4.86).
4. During much of the last interglacial period, temperatures were 3C higher than they are today with far lower CO2 levels.
5. Dating way back into prehistory 100s of millions of years ago, CO2 concentrations were often several multiples higher than today, yet temperatures never went way up or out of control (i.e. past a tipping point), and ice ages still occurred.
6. The absorption spectrum of CO2 is already mostly saturated, which means it takes a huge amount of added CO2 just to get a slight increase in total net absorption. That is, on the logarithmic scale, it has already reached the point significantly diminished returns.
7. The 3.7 W/m^2 of total net absorption increase per CO2 doubling is only a theoretical measurement taken from ‘nominal’ GHG concetrations. (i.e. it is not the equivalent of a laboratory measurement). This means there is no guarantee that the total absorption will actually increase by 3.7 W/m^2 (or even increase at all).
8. The amount of temperature increase in the last 30 years is inconsistent with net positive feedback acting on the climate, even if the added CO2 is the primary cause of the warming.
9. During the last interglacial period, for over two thousand years it was about 3C (or more) warmer than today, yet Greenland and Antarctica did not melt (if they did we wouldn’t have ice cores dating back past that time).
10. Biology likes warmth and added CO2 drives plant growth which is the primary fuel for the entire biosphere, as well as fuel for agriculture which helps feed the world’s population (far too much of which is still starving).
RW,
Your point #1 is a classic straw man argument that disproves something that no one actually believes. CO2 lagging temperature during glacial/interglacial transitions only means that CO2 wasn’t the initial cause. I think you would find it hard to locate citations in the literature that make the argument that CO2 was the initial cause. The current consensus is that it’s Milankovitch cycles that cause highly variable insolation at high northern latitudes while not changing global insolation. Those variations encourage ice formation or melting with resultant albedo feedback. Over thousands of years, the warming or cooling of the ocean changes the atmospheric CO2 concentration which provides additional feedback. It’s therefore expected that CO2 would lag temperature for this case.
Dewitt,
My point is the additional CO2 is only a small contributing factor – not that it’s a zero factor. If it was a significant factor then it stands to reason the lag when temperatures are falling should not be longer but shorter.
Dewitt,
“CO2 lagging temperature during glacial/interglacial transitions only means that CO2 wasn’t the initial cause.”
Yes, I’m aware of this.
I agree with Bryan that some sort of falsification parameters should be and need to be laid out.
arcanitecartel == TedH … not sure why it did that
RM,
Let me just say, I’m not trying to convince anyone of anything. Just myself. Also, I’ll say that I’m not a professional scientist. So anything a professional may have available at their fingers I wouldn’t necessarily have. That said, here’s my comment on your points.
Points 1,4,5. Interesting. Good information to have. But I don’t see them as falsifying the CAGW hypothesis. The hypothesis doesn’t require that temperature rises today have the same cause as they did thousands or millions of years ago. As I understand it, there is a feedback cycle between CO2 levels and temperature. If something drives up temperature outside of that feedback cycle (i.e. something other than CO2) there will be a consequent rise in CO2 as well (released from warmer ocean waters) and you would expect in that case for CO2 to lag temperature.
Regarding 7. I don’t see why theoretical calculations are to be disregarded. As I understand it, this is based on sound principles which pre-date the CAGW. Also, I have seen several studies involving comparison of the theoretical calculations and measurements by pyrgeometers and they look like they agree very well to me.
Regarding #8. Let me ask you…in what way is it inconsistent? Adding energy to the earth’s thermodynamic system doesn’t mean that all of it goes into raising the temperature all the time.
10. This, to me, seems like a gross over-simplification, much in the same manner as my office-mate reduced everything to “it’s the sun, it’s the sun, you know what I’m saying”. Yes, biology likes warmth … to a point. And its all the details around that which really matter in the end. I can grow my yogurt cultures by keeping them warm, but one degree to high and its all over. Yes, plants need CO2. They also need water and the right temperature to grow as well as the right amount of sunlight, nitrogen, and so on. The point being… does this climatic change push the environment out of the range in which we as humans, and the animals and plants we depend on, require.
“Points 1,4,5. Interesting. Good information to have. But I don’t see them as falsifying the CAGW hypothesis. The hypothesis doesn’t require that temperature rises today have the same cause as they did thousands or millions of years ago.”
Overtly falsifying – no, but they are inconsistent with, I think.
“As I understand it, there is a feedback cycle between CO2 levels and temperature. If something drives up temperature outside of that feedback cycle (i.e. something other than CO2) there will be a consequent rise in CO2 as well (released from warmer ocean waters) and you would expect in that case for CO2 to lag temperature.”
I don’t find this convincing at all. The changes in energy distribution as a result of orbital changes appear to explain very well the glacial to interglacial cycles. There is no need to illicit a CO2 induced effect to explain them. The orbital changes are like multiple 10s of W/m^2, where as the CO2 change is not not even half of one doubling.
“Regarding #8. Let me ask you…in what way is it inconsistent? Adding energy to the earth’s thermodynamic system doesn’t mean that all of it goes into raising the temperature all the time.”
The inconsistency is in the magnitude of the effect.
Well, if you care to provide the calculations as to the inconsistency in the magnitude of the effect….
And I think you missed my point, which was that a temperature rise in millenia past do not necessarily have to have the same cause as a temperature rise today. My point was, if something else did cause the temperature rise in the past, then a CO2 rise lag is logical and expected, but has nothing to do with what’s happening today. Someone here (and others elsewhere) suggest that this cause is the Milankovich cycle.
TehH,
“And I think you missed my point, which was that a temperature rise in millenia past do not necessarily have to have the same cause as a temperature rise today.”
Yes of course I agree with this (who wouldn’t?).
AGW is not a theory, it’s an outcome of the well known and thoroughly verified theory called physics. The details are too difficult allow for precise predictions for climate, but the thoery does produce many partial results. This whole site is about, what we can learn reliably from physics.
AGW can be falsified by pointing out severe errors in the calculations that appear to prove beyond much doubt that additional CO2 has an warming effect. Nobody has presented such arguments, when we exclude claims that have essential explicit errors in them.
Further empirical studies and refinement of the calculations will provide better estimates for the strength of the warming influence of CO2 (i.e. the climate sensitivity ECS). It’s possible that ECS is significantly less than the present best estimates indicate. Through that it’s possible that AGW is not a serious issue. IPCC does not claim that AGW is with certainty a serious threat, but IPCC does claim that AGW is likely to be non-negligible and that there is a high probability of serious damage, if CO2 emissions continue for long at high level.
The seriousness of AGW is a quantitative question, not one with an answer of yes or no. Therefore the whole concept of falsification does not apply to it at a general level. Fundamental theories are falsifiable, quantitative predictions can be found to be accurate or erroneous.
All the important questions concern the future: How much warming will come out, and what are the consequences of that warming. All the questions on the past are significant only to the extent they help in answering these important questions.
The rapid rise of temperatures up to 2000 (or 1998) led many to expect similarly rapid warming to continue. Now we know that that has not been the case. The most likely explanation is that natural variability added to the warming before 2000 and has essentially canceled the warming for about 15 years. That makes it likely that a new period of rapid warming will be seen at some moment, perhaps very soon, perhaps a little later. Whether that is, indeed, the case or not, the best present estimate for the climate sensitivity is somewhat lower than the best estimate done 10 years ago based on data available then.