Some Green readers have probably heard by now that a draft of the next big United Nations report on climate change has leaked.
The agent of the leak is a rather colorful climate contrarian named Alec Rawls, who essentially claimed, on the basis of a single sentence in the draft, that the entire edifice of climate science is about to collapse. In his interpretation, the group putting the report together, the Intergovernmental Panel on Climate Change, is about to acknowledge the validity of a longstanding fringe theory: that cosmic rays have a huge influence on the earth?s climate.
This claim turns out to be an overstatement, to say the least. But first, what do the leak and the accompanying flurry of reaction on blogs tell us about the United Nations exercise of periodically summarizing climate science?
These reports come out roughly every five years. They are unlike anything else in science that I know of: an attempt to digest the many thousands of relevant papers and discern a global scientific consensus about the state of climate science, the likely impacts of climate change, and the policies that might be effective in countering the risks.
The exercise is a special type of response to a unique global problem. Ultimately, the reports are supposed to help governments decide what steps to take to act on their own stated commitment under a global treaty to ?prevent dangerous anthropogenic,? or human, ?interference with the climate system.?
The I.P.C.C. has won accolades over the years, most notably the 2007 Nobel Peace Prize. But the reports have also become political lightning rods. Climate-change contrarians, though they publish very little in the relevant scientific literature, use the Internet to mount persistent attacks on the I.P.C.C. Being a human enterprise, the I.P.C.C. has certainly made mistakes, and these get magnified by people attempting to generate doubt about the overall body of climate science.
I?ve had conversations with several mainstream scientists who have their own doubts about the continuing value of the whole exercise. Some of them think the I.P.C.C. reports have become a too-convenient target. Most of these folks continue to participate, though. One top scientist, Ken Caldeira, caused a stir last year when he resigned as a lead author, saying he was confident in the other authors and felt that his own time could be put to better use.
Some other scientists, and a lot of environmental campaigners, feel the I.P.C.C. is just too cautious and too bureaucratic to make contributions to the global discourse that matter in real time. In their view, climate change itself is outrunning the statements that scientists are able to make about it through such a ponderous mechanism.
As best as I can tell, the majority of climate scientists hold a moderate view: that the I.P.C.C. certainly has its problems but remains a valuable forum for helping governments and the public understand the vast complexities of the field.
Now, as to the leak at hand, what does it tell us?
The first thing to say is that the document is a draft and is right now undergoing revisions that could turn out to be extensive. That means nothing in it yet represents the official position of the I.P.C.C. or the governments that appointed it.
That said, assuming that the current language survives revision, the top-line findings are not going to be especially surprising to anyone. The last I.P.C.C. report, in 2007, made headlines by going beyond the previous three reports, concluding on the basis of accumulating evidence that ?most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.?
The draft report pushes only a little beyond this language, saying it is ?virtually certain? that greenhouse gases released by human activities are causing an energy imbalance that is warming the earth, and finding ?very high confidence? that natural drivers of climate change are causing only a small fraction of that imbalance.
Again, assuming the draft language survives, this will be the single most important conclusion:
It is extremely likely that human activities have caused more than half of the observed increase in global average surface temperature since the 1950s. There is high confidence that this has caused large-scale changes in the ocean, in the cryosphere, and in sea level in the second half of the 20th century. Some extreme events have changed as a result of anthropogenic influence.
For anyone who has been following climate science closely the last few years, this is pretty much exactly what you would expect the next I.P.C.C. report to say. So what is it that got Mr. Rawls excited enough to leak the draft? (He got his hands on it by signing up to be an official reviewer, as virtually anyone can do, and then breaking his pledge to keep the draft confidential.)
The backdrop is that, in their quest to prove that anything other than human-generated greenhouse emissions are the cause of global warming, climate contrarians have seized on a theory promulgated by a Danish scientist named Henrik Svensmark. He believes that cosmic rays modulated by the sun exercise a substantial influence on the earth?s climate.
Some scientific results issued by Dr. Svensmark and others may turn out to be initial steps toward establishing the theory. The idea is a long, long way from being proven, however. Gavin Schmidt, a scientist at NASA, has outlined the missing steps here and further dissected the issue here. For more of a grounding in the basics, you can go here.
In this discussion, scientists often use the abbreviation G.C.R. for galactic cosmic ray. The sentence that fired Mr. Rawls? imagination is the one in bold within the following paragraph:
Many empirical relationships have been reported between G.C.R. or cosmogenic isotope archives and some aspects of the climate system? The forcing from changes in total solar irradiance alone does not seem to account for these observations, implying the existence of an amplifying mechanism such as the hypothesized G.C.R.-cloud link. We focus here on observed relationships between G.C.R. and aerosol and cloud properties.
Mr. Rawls found this to be a ?game-changing? acknowledgement that, yes, earthly climate must be influenced by cosmic rays. Indeed, in his manifesto leaking the document, he called this sentence ?an astounding bit of honesty, a killing admission that completely undercuts the main premise and the main conclusion of the full report, revealing the fundamental dishonesty of the whole.?
Well.
Looking at the full report, I have to wonder if Mr. Rawls just stopped reading when he got to that sentence. Because what follows is a lengthy discussion of the science to date regarding cosmic rays and climate, one that points out the intriguing results suggesting a possible connection, but also points out that many of those studies cannot be reproduced by other scientists, that many of the supposed correlations are weak, and so forth. (To read the whole discussion for yourself, download Chapter 7 here or, if that has crashed again, as happened earlier, try here and click ?create download link.? Go to Section 7.4.5.)
That single sentence may, in fact, be inartfully worded, giving more credence to the cosmic ray theory than it deserves ? and I?m guessing the I.P.C.C. authors will now take a closer look at it. But as I read it, the full discussion is a balanced recitation of what we know so far, a diligent attempt to take the published science into account, including the many holes in the theory ? exactly what one would hope for from the climate body.
The discussion concludes, explicitly, that evidence of a connection between cosmic rays and climate is quite weak. That is not the same as saying it won?t be proven some day, but it certainly has not been proven yet.
My interpretation of all this appears to be confirmed by a statement from Steve Sherwood, a climate scientist at the University of New South Wales who is a lead author of the chapter in question. He told the blogger Graham Readfern:
The single sentence that this guy pulls out is simply paraphrasing an argument that has been put forward by a few controversial papers (note the crucial word ?seems?) purporting significant cosmic-ray influences on climate. Its existence in the draft is proof that we considered all peer-reviewed literature, including potentially important papers that deviate from the herd. The rest of the paragraph from which he has lifted this sentence, however, goes on to show that subsequent peer-reviewed literature has discredited the assumptions and/or methodology of those papers, and failed to find any effect. The absence of evidence for significant cosmic-ray effects is clearly stated in the executive summary. This guy?s spin is truly bizarre. Anyone who would buy the idea that this is a ?game changer? is obviously not really looking at what is there.
There you have it. For those who can?t get enough of this flap, go to the invaluable Skeptical Science Web site, where Dana Nuccitelli has further deconstructed Mr. Rawls?s argument.
Here?s the real kicker, as Mr. Nuccitelli points out: if the supposed cosmic ray mechanism were valid, and as strong as the climate contrarians want to believe, the earth should be cooling rather sharply right now. But it is doing nothing of the sort.
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