3.5 Changes in Atmospheric Circulation

Changes in the circulation of the atmosphere and ocean are an integral part of climate variability and change. Accordingly, regional variations in climate can be complex and sometimes counter-intuitive. For example, a rise in global mean temperatures does not mean warming everywhere, but can result in cooling in some places, due to circulation changes.

This section assesses research since the TAR on atmospheric circulation changes, through analysis of global-scale data sets of mean sea level pressure (MSLP), geopotential heights, jet streams and storm tracks. Related quantities at the surface over the ocean, including winds, waves and surface fluxes, are also considered. Many of the results discussed are based on reanalysis data sets. Reanalyses provide a global synthesis of all available observations, but are subject to spurious changes over time as observations change, especially in the late 1970s with the improved satellite and aircraft data and observations from drifting buoys over the SH. See Appendix 3.B.5 for a discussion of the quality of reanalyses from a climate perspective.