Carl-Gustaf Rossby's work leading to the dispersion equation for his eponymous atmospheric wave form was motivated by his quest to understand interrelationships between fluctuations in the zonal mean wind and the quasi-stationary waves. Rossby believed that climate variability on almost all timescales could be understood in terms of changes in the frequency of occurrence of states of high and low zonal index. Using modern-day terminology and ideas, Rossby's perception of climate variability can be viewed in terms of low-frequency changes to the probability distribution of the nonlinear weather regimes that characterize our chaotic climate attractor.

A perspective on possible future climate change is outlined, based on these ideas. One of the most basic notions to emerge is that even if such change is predominantly anthropogenically induced, its manifestation may be predominantly onto the natural “modes” of variability of the climate system.

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Editor's note: This is the second of a series of papers about Carl-Gustaf Rossby that will be published in the Bulletin. All papers were presented at the 1998 Annual Meeting of the American Meteorological Society as part of the Special Session Honoring the Centennial of the Birth of Carl-Gustaf A. Rossby. Other papers in the series will appear in upcoming issues of the Bulletin.