Global Warming and the Weakening of the Tropical Circulation

• Published in: Journal of climate Vol. 20; no. 17; pp. 4316 - 4340
• Main Authors: Vecchi, Gabriel A., Soden, Brian J.
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01.09.2007
• Subjects: Archives & records; Atmospheric circulation; Atmospheric models; Atmospherics; Boundary layer; Change detection; Circulation; Climate change; Climate models; Climatology. Bioclimatology. Climate change; Dipoles; Earth, ocean, space; El Nino; El Nino phenomena; Exact sciences and technology; External geophysics; Gases; General circulation. Atmospheric waves; Global climate models; Global warming; Greenhouse effect; Greenhouse gases; Humidity; Intergovernmental Panel on Climate Change; Meteorology; Mixed layer; Modelling; Ocean circulation; Ocean currents; Ocean dynamics; Ocean warming; Oceans; Physics of the oceans; Precipitation; Scaling; Sea level changes; Sea level pressure; Temperature; Thermal circulation; Thermal structure; Thermohaline structure and circulation. Turbulence and diffusion; Tropical atmosphere; Tropical circulation; Tropical climates; Updraft; Water circulation; ISW, Indian Ocean; IS, Tropical Pacific; Century 21st; Indian ocean dipole; North south asymmetry; Carbon dioxide; tropical zone; Climate models; digital simulation; ocean-atmosphere interaction; Forecast model; troposphere; greenhouse gas; Dynamical climatology; intensity; Walker circulation; climate modification; global change; warming; Air pollution; atmospheric circulation; ocean circulation
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/jcli4258.1

This study examines the response of the tropical atmospheric and oceanic circulation to increasing greenhouse gases using a coordinated set of twenty-first-century climate model experiments performed for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The strength of the atmospheric overturning circulation decreases as the climate warms in all IPCC AR4 models, in a manner consistent with the thermodynamic scaling arguments of Held and Soden. The weakening occurs preferentially in the zonally asymmetric (i.e., Walker) rather than zonal-mean (i.e., Hadley) component of the tropical circulation and is shown to induce substantial changes to the thermal structure and circulation of the tropical oceans. Evidence suggests that the overall circulation weakens by decreasing the frequency of strong updrafts and increasing the frequency of weak updrafts, although the robustness of this behavior across all models cannot be confirmed because of the lack of data. As the 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 and are reproduced in both mixed layer and full ocean dynamics coupled climate models. The character of the Indian Ocean response to global warming resembles that of Indian Ocean dipole mode events. The consensus of model results presented here is also consistent with recently detected changes in sea level pressure since the mid–nineteenth century.