This week brings news of 1) a dramatic improvement in the estimates of how soil carbon content is related to atmospheric carbon concentration and 2) the exposure of some really crappy work on the rate of melting of Himalayan glaciers by the International Panel on Climate Change (IPCC). The soil carbon work is Good Data, but Bad News if you care about the effects of high atmospheric carbon concentrations, while the Himalayan glacier story is all about terrible peer review and Bad Data (non-existent data, actually), which doesn't help anybody figure out the real story on water supplies in Asia.
First up, a paper from this week's PNAS by Breeker et al at UT Austin, "Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for A.D. 2100". Already from the title you can see where this is going.
The problem Breeker and colleagues address is the following: how do you correlate the carbon content of fossil soils with prevailing atmospheric carbon dioxide concentrations? Well established methods exist for measuring the carbon content of compounds in fossil soil, but less certain were conditions under which chemical reactions produce those particular compounds. It turns out that model used to infer atmospheric CO2 contained an error. Breeker determined that the primary compound assayed when determining soil carbon content forms at much lower atmospheric CO2 concentrations than had been assumed.
Prior attempts to correlate soil carbon (and by proxy atmospheric CO2) with greenhouse periods in Earth's climate had concluded that warm periods experienced CO2 concentrations of much greater than ~1000 parts per million (ppm). Therefore, one might conclude that only when average atmospheric CO2 spiked above this level would we be in danger of experiencing greenhouse gas warming that threatened glaciers. The correction supplied by Breeker substantially lowers estimates of the average CO2 concentration that is correlated with continental glacial melting. Eyeballing the main figure in the paper, it looks to me like we could be in real trouble above 450 ppm -- today we are at just shy of 390 ppm and there is no sign we will be slowing down anytime soon, particularly if India and China keep up their pace of development and emissions.
Looking forward to 2100, things get a touch squiffy because Breeker relies on an estimate of CO2 concentrations that come out of model of global economic activity. So the title of the paper might be a tad alarmist, simply because 2100 is a long way out for any model to be taken too seriously. But the correction of the paleodata is a big story because at minimum it reduces the uncertainty of atmospheric CO2 levels, and it appears to clarify the connection between CO2 levels and continental glaciation. More work is needed on the later point, obviously, or this paper would have been on the cover of Science or Nature.
Now on to a serious screw-up at the IPCC. Elisabeth Rosenthal at the NYT is reporting that "A much-publicized estimate from a United Nations panel about the rapid melting of Himalayan glaciers from climate change is coming under fire as a gross exaggeration." Here is Andrew Revkin's take on DotEarth, and anyone interested in this story should read through his post. The comments are worth perusing because some of the contributors actually seem to have additional useful knowledge, though, of course, nut jobs aplenty show up from both sides of the debate over climate change.
In a nutshell, the issue is that the most recent IPCC chapter on glaciers contained a conclusion, advertised as real analysis, that was in fact a speculation by one scientist promulgated through the popular press. The authors of that section of the IPCC report may have been warned about the unsubstantiated claim. Contradictory data and analysis seems to have been ignored.
So, to be frank, this is a giant, inexcusable fuck-up. The IPCC is composed of so many factions and interest groups that this may be a case of simple blundering or of blatant politicization of science. But here is the beautiful thing about science -- it is self-correcting. It may take a while, but science always wins. (See also my post of a couple of years ago, Dispelling a Climate Change Skeptic's "Deception".) Every newspaper story I have seen about this particular IPCC screw-up notes that it was brought to light by...wait for it...a climate scientist. It is an excellent public airing of dirty laundry by the community of science. So while this episode demonstrates that the last official IPCC report on glacial melting in the Himalayas should not be used for any sort of scientific policy recommendation or economic forecast, you can bet that the next report will do a damn fine job on this topic.
Finally, whether or not the IPCC gets its act together, there are plenty of good data out there on the state of the planet. Eventually, Science -- with a capital S -- will get the right answer. The same methodical process that has resulted in computers, airplanes, and non-stick fry pans will inevitably explain what is really going on with our climate. And if you use computers, fly on airplanes, or eat scrambled eggs then you are implicitly acknowledging, whatever your political or religious persuasion, that you believe in science. And you better, 'cause science always wins.