If we can all avert our eyes for a moment from the CRU emails, the inexorable momentum of climate science hurtles down the track with a new paper in today’s Science using paleo records to suggest (among many interesting things) that a warming world is, for the southwestern US, a drier world.
Mike Mann and colleagues (yeah, I know, get your mind off the emails, dammit!) have used a network of proxies in an attempt to reconstruct spatial variability for the Medieval Warm Period and Little Ice Age. For those of us in the Southwest, the reconstruction of sea surface temperatures in the equatorial Pacific is of particular import. The paper supports an argument Mann and others have previously made that the MWP was characterized by persistent La Nina-like conditions, a cooling along the equator that, among other things, leads to generally drier conditions here in the Southwest.
Mann and others (see Volcanic and Solar Forcing of the Tropical Pacific over the Past 1000 Years, Journal of Climate, Vol. 18, 447-456) have argued in the past for a sort of “thermostat” mechanism, where generally warm conditions create a cool anomaly in the Pacific, a “thermostat effect”. From the new paper:
The paleoclimate reconstructions presented here hold important implications for future climate change. For example, if the tropical Pacific thermostat response suggested by our analyses of past changes applies to anthropogenic climate change, this holds profound implications for regional climate change effects such as future drought patterns.