PerspectiveAtmospheric Science

Ocean Effects of Blocking

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Science  04 Nov 2011:
Vol. 334, Issue 6056, pp. 612-613
DOI: 10.1126/science.1214167

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Variations in the circulations of the Atlantic Ocean and the atmosphere above it influence societies far beyond the ocean basin itself. Scientists have long tried to understand and predict the dramatic year-to-year variability of the North Atlantic Oscillation (NAO) (1), but modeling the associated ocean-atmosphere interaction remains a challenge (2). Attention has turned to longer-term warming and cooling episodes of the North Atlantic Ocean. These variations—often referred to as Atlantic multidecadal variability (AMV)—are widely assumed to arise from variability in the ocean's overturning circulation (3), in which warm water flows northward near the ocean surface and returns southward at depth. In contrast, Häkkinen et al. argue on page 655 of this issue (4) that the AMV owes its existence to atmospheric events with time scales as short as a week.