18 December 2009

More to Climate Change Evidence than Just Tree-Ring Records

Posted by Michael McFadden

Tons of climate scientists were here in San Francisco this week; many of their policy counterparts were in Cophenhagen, trying to put together some kind of consensus plan for how to deal with global climate change. Their job got a lot more daunting a few weeks ago, when leaked emails from the Climate Research Center at the University of East Anglia were “leaked” to the general public.

One of the major “controversies” that the news media blew up was the issue of the dendrochronological record: the tree-ring record, which before 1960 matches measured temperature records very well, for some reason stopped responding to increases in temperature. Climate skeptics criticize scientists for simply chopping off the record after 1960 or so, claiming (amongst many other things) that because the tree-ring record doesn’t show increasing temperatures, climate change must not be happening.

So the sessions PP52A and PP53A, Decadal- to Century-Scale Climate Variability Over the Past Millennium: Evidence From Non-Tree-Ring Archives, which went on this morning and afternoon, was particularly well-timed. Yeah, the tree-ring data doesn’t show that the world has been warming since 1960, but the whole of climate science isn’t based on one proxy—there are plenty of other methods by which scientists measure temperature changes, and there are plenty of well-tested, reliable proxies that provide evidence for recent climate change.

Image from NOAASeveral researchers—like Casey Saenger, from Yale—showed distinct warming trends in well-constrained coral records from the Caribbean. Others, like Julia Richey, from the University of South Florida, used foram proxies (Mg/Ca temperature records) and chrenarchaeota (TEX-86 temperature reconstructions) to track Holocene sea surface temperature trends—they saw late-Holocene warming, as well. Jeffrey Salacup, from Brown, used alkenones in the Narragansett Bay to reconstruct the temperature and productivity history of the bay, also observing anthropogenic impacts.

I could go on, but the point of the session was clearly that though Holocene climate records were historically based on terrestrial, Northern Hemisphere proxies like the dendrochronological record, there are plenty of robust records from around the world that are neither Northern Hemisphere nor terrestrial, that show the same thing: warming in the late Holocene. Climate change is not a hoax, world—let’s hope the policy makers of the world have put together a good plan for us to mitigate our future impacts.

–Ale Borunda, Columbia University Earth and Environmental Sciences Journalism Graduate Student