ABSTRACT
This chapter examines whether and with what level of certainty such changes in polar climate may be directly attributed to human activity. There are several large-scale modes of atmospheric circulation variability that influence climate across all or part of the Arctic region and such sources of climate variability need to be accounted for when attempting to attribute regional climate change to an anthropogenic source. The North Atlantic Oscillation is the major mode of extra-tropical atmospheric circulation variability in the Northern Hemisphere and plays a key role in determining the Arctic climate. The Southern Annular Mode (SAM) is the principal mode of atmospheric circulation variability in the Southern Hemisphere extra-tropics and has a huge influence on Antarctic climate. J. P. Nicolas and D. H. Bromwich showed that the SAM trends have had a statistically significant cooling effect in East Antarctica in both summer and autumn and also West Antarctica in the latter season only.
