Abrupt Climate Change

I’ve been guilty in my journalism of playing the “thermohaline card” – using the example of a thermohaline circulation shutdown as an example of the sort of abrupt climate change that could happen unexpectedly as a result of anthropogenic climate change. I never pushed it hard, but I thought it relevant. But a good story from Richard Kerr in the Oct. 21 Science has me convinced I shouldn’t do it again. It’s not that abrupt climate change isn’t an important issue, a legitimate driver behind a “precautionary principle” attitude toward greenhouse gas reduction. But a shutdown of the thermohaline circulation, with the resulting scary European deep freeze scenario, seems less credible than I used to believe:

A precipitous shift in climate could happen again, say researchers, 25 of whom gathered here last summer to discuss abrupt climate change.* But the prime menace no longer lies in the North Atlantic. Instead, a growing contingent of scientists now sees the North Atlantic as no more of a threat than accelerating sea level rise, megadroughts, and monsoon failures. “A few years ago, people thought the [Atlantic circulation] could collapse almost like The Day After Tomorrow,” said paleoclimatologist Julia Hargreaves of the Frontier Research Center for Global Change in Yokohama, Japan. “But a very rapid collapse now seems fairly unlikely under global warming.”

* The “here” he mentions above is the “Abrupt Climate Change: Mechanisms, Early Warning Signs, Impacts, and Economic Analyses,” meeeting in July Aspen under the auspices of the Aspen Global Change Institute.