One of the commenters to my last post, an attempt to explain why the hacked climatology emails do not constitute a scientific scandal, came up with a darn fine idea:
If you think that global warming rests on a few temperature data sets and models, you are very wrong. If you don’t understand this then you don’t know enough to have an opinion on the subject, and you most likely will be treated just like any other ineducable troll.
Grab a climate textbook and do some reading…it will help if you have some physics background too. Yeah, science takes effort…
I just happen to have at hand a brand new textbook on the very subject at hand. It’s called Paleoclimates: Understanding Climate Change Past and Present, by Thomas M. Cronin of Georgetown University, Columbia University Press, 2009. ( I have no idea why the CUP folks decided I would be an appropriate reviewer deserving a free copy of $95 textbook, but I haven’t bought a book with my own money in more than four years thanks to this blogging gig and I’m happy to accept this one, too.)
As has been pointed out numerous times, nothing in the stolen emails and other documents that found their way onto the Internet last week in any way challenges the science behind anthropogenic global warming. But a lot of the material does deal with one particular subfield of climatology, dendrochronology, the science of which appears to confuse just about everyone who doesn’t study the subject for a living.
I’m no expert, but Cronin is, and on page 312 he address the very issue that has so many amateurs puzzled. Specifically, what do climatologists mean when they write about “hiding the decline” in tree-ring proxies? It sounds bad, but it really isn’t. The Real Climate gang explained it, and rather well I think. But many remain unconvinced. So let’s turn to the text, specifically the section titled “Proxy limitations — Divergence and Segment Length Curse,” shall we?
… no tree ring-based reconstructions of northern hemisphere temperatures that includes the 1990s is able to capture the range of late 20th century warming seen in the instrumental records. This means that instrumental records show warming, but reconstructed temperatures from trees show cooling or no change.
That excerpt appears immediately above a graph that shows how temperatures inferred from tree-ring records since about 1850 (the “proxies”) are a pretty good match for actual temperature records derived from thermometers right up until the 1980s. After that, the tree-ring data begin to show lower temperatures than were actually recorded.
Just why tree rings no longer provide useful proxy data for temperatures is not known. There are several theories, many of which suggest that climate change itself is the problem. Trees no longer grow as they once did before the climate started changing so rapidly. But the point is, there is no question that tree-ring growth rates of the past — before we had thermometers — can serve as useful proxies for historical temperature data. They are much less useful now, but that doesn’t matter so much because we have actual temperature records. All of this was sorted out back in 1998. It’s not new, nor even particularly interesting, to anyone familiar with the science.
This is why those working with tree-ring data want to “hide” the decline in recent decades; they know the data aren’t useful. Perpetual thorn-in-the-side-of-actual-climatologists Steve McIntyre fails to grasp this simple issue when he questions the usefulness of dendrochronology data to support global warming models. And so, it would appear, do a large number of climate change pseudoskeptics who remain convinced the stolen emails paint a picture of scientists trying to obfuscate or distort climate records.
Incidentally, in case anyone wants to suggest that Cronin is somehow complicit in the alleged coverup, the author repeatedly takes great pains in his text not to come across as a climate change alarmist. I would say he actually goes too far in the opposite direction. In one section he even wastes a quarter of a page discussing the controversial 2003 paper in Climate Research by Soon and Baliunas that convinced half the journal’s editorial board to resign in protest over a failure of the peer-review process. The very paper and journal that some of the stolen emails discussed in a manner that led many of the pseudoskeptics to conclude mistakenly that there was a coordinated attempts at scientific journal censorship.
No one takes Soon and Baliunas seriously in climatology circles, and Cronin does point out the serious flaws in their paper, which tried to argue that “the 20th century is probably not the warmest nor a uniquely extreme climatic period of the last millennium.” But by including the paper, even as an example of flawed analysis, in a textbook, he’s probably doing them a favor they don’t deserve.
So, thanks, commenter Daniel J. Andrews. Turning to a textbook was a fine idea. For those don’t have a recent climatology text handy, well, maybe it would be best if we let gave the benefit of the doubt to the scientists.
And if you made it this far, please turn to Carbon Fixation for what is the definitive commentary on the whole affair: “Global Warming and Climate Change: Phrases of the decade Newtongate: the final nail in the coffin of Renaissance and Enlightenment ‘thinking’“