HR: 15:30h
AN: A24A-01    [Abstracts]
TI: Charney Lecture: Interpretation of recent climate change
AU: * Thompson, D W
EM: davet@atmos.colostate.edu
AF: Dep't. of Atmospheric Science, Colorado State University, Fort Collins, CO 80523 United States
AB: The observed climate change of the past few decades is characterized not only by increases in global mean temperatures, but also by substantial changes in the structure of the atmospheric circulation. In this overview talk, I will review the observed changes in the atmospheric flow, discuss the implications of these changes for regional weather, and outline a series of possible causal mechanisms. In both hemispheres, recent changes in the extratropical circulation are dominated by trends in the extratropical zonal flow that extend from the surface of the Earth to the middle stratosphere. In the Northern Hemisphere, the circulation trends are largest in winter, and account for a substantial fraction of recent changes in such widely varying fields as Arctic sea-ice, precipitation over Europe, and temperatures throughout North America and northern Eurasia. The Northern Hemisphere trends were substantial through the late 1990s, but have relaxed in recent years. In the Southern Hemisphere, the circulation trends peak during the summer months, and have contributed to much of the observed cooling of eastern Antarctica and a portion of the warming of the Antarctic Peninsula during that season. It is argued that a substantial fraction of the Southern Hemisphere trends can be traced to anthropogenic emissions of stratospheric ozone-depleting gases. Northern Hemisphere stratospheric ozone depletion is likely too small to account for the trends there, and it remains unclear how increasing greenhouse gases will impact the extratropical circulation in either hemisphere. The recent trends in the extratropical circulation are juxtaposed against an unanticipated cooling maximum in the tropical stratosphere, where temperatures have decreased by several K over the past few decades. The tropical stratospheric cooling maximum is readily apparent at virtually all radiosonde stations, but is not expected based on numerical simulations of recent climate change.
DE: 1610 Atmosphere (0315, 0325)
DE: 3319 General circulation
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly