Brian Soden

The University of Miami

Global Warming and the Weakening of the Tropical Circulation

Room 811 AOSS, Monday, Feb. 26, 2007, 3:30 PM

Abstract

This study examines the response of the tropical atmospheric and oceanic circulation to increasing greenhouse gases using a coordinated set of 21st Century climate model experiments performed for the IPCC AR4. The strength of the atmospheric overturning circulation is shown to decrease as the climate warms. This decrease is a robust result of all models and supported by simple thermodynamic arguments. The weakening occurs preferentially in the zonally–asymmetric rather than zonal–mean component of the tropical circulation and is shown to induce substantial changes to the thermal structure and circulation of the tropical oceans. As climate warms, changes in both the atmospheric and ocean circulation over the tropical Pacific Ocean resemble "El Niño"–like conditions; however, the mechanisms are shown to be distinct from those of El Niño. The consensus of model results are also consistent with recently detected changes in the tropical circulation during the 20th Century.