A record number of tropical storms and hurricanes formed in the North Atlantic last year (SN: 12/24 & 31/05, p. 406: Available to subscribers at Beyond the ABC’s: North Atlantic posts record hurricane season). One factor driving this unprecedented activity was the unusually warm waters there, and global warming was largely to blame, says Kevin E. Trenberth, an atmospheric scientist at the National Center for Atmospheric Research in Boulder, Colo.
Between June and October 2005, the average sea-surface temperature in the region between Africa and the Caribbean where such storms typically form was 0.92°C above the average recorded there between 1901 and 1970. That 70-year period predates a recent surge in temperatures worldwide, report Trenberth and Dennis J. Shea, also of the center.
By analyzing oceanographic data gathered around the world, Trenberth and Shea estimate that less than 0.1°C of last year’s North Atlantic temperature anomaly resulted from long-term variations in a regional climate cycle called the Atlantic Multidecadal Oscillation. About 0.2°C stems from the aftereffects of an El Niño.
About 0.45°C comes from climate changes that boosted sea-surface temperatures worldwide. The remainder of the anomalous warmth, around 0.2°C, reflects normal year-to-year variation in weather, Trenberth and Shea report in the June 28 Geophysical Research Letters.