Atmospheric Regimes: Their Recent Behavior and Future Change

Northern Hemisphere low-frequency atmospheric variability over recent decades is examined for nonlinear regime behavior. Nonlinear regimes are shown to exist during this period with their number and character depending on the time-scales retained in the analysis. The relationship between nonlinear regimes and the Arctic and North Atlantic Oscillations will be discussed. A coupled global climate model reproduces this historical behavior and predicts significant future change under enhanced greenhouse gas and aerosol forcing. These results offer a new perspective on historical atmospheric variability and predicted 21^st century change.