Climate change and the tropical Pacific: The sleeping dragon wakes

Abstract

The global impact of the tropical Pacific atmosphere–ocean system has been extensively studied in connection with the El Niño cycle. There is reason to believe that the system may also hold the key to rapid reorganizations of climate leading to changes that persist from centuries to millennia. The unusually steady climate of the past 10,000 years, after the ultimate recovery from the Younger Dryas cold reversion, has provided a congenial home for the rise of civilization. This era contrasts with the Last Glacial Maximum and other cold periods of the Pleistocene, which were beset by erratic, rapid, and large-amplitude climate reorganizations with no obvious astronomical pacemaker. The mechanism of these millennial scale climate changes is not known (see ref. 1 for some current thinking on the matter); given that we don't know what accounts for the unusual stability of the recent climate, we don't know what it would take to break it. This thought is unsettling in a world seemingly committed to substantial warming from anthropogenic CO2 increases in the next 2 centuries. Attention has focused on the Atlantic thermohaline circulation (THC) as the “Achilles heel” of climate, primarily because many of the abrupt climate change events of the past 100,000 years are known to have been accompanied by abrupt transitions in the THC (2). There is a need to consider other possibilities, not least because atmospheric general circulation models fail to respond to a THC shutdown with a global signal of the character and magnitude that seems to be called for by the data. Is the failure of atmospheric models to yield the required response symptomatic of some fundamental flaw in the current models, or is the resolution of the puzzle to be found in some trigger other than THC shutdown? The answer to this question would tell …