Jake Crouch of the National Climatic Data Center recaps the temperature patterns of 2011, emphasizing the much greater than average warmth across Arctic latitudes and the influence of La Niña in the tropical Pacific.
Following a brief interlude of “neutral” sea surface temperature conditions this summer, La Niña has returned to the tropical Pacific Ocean. The cool phase of the El Niño-Southern Oscillation climate pattern is expected to persist through winter.
Between January and April 2010, temperatures in the Pacific were under the warming influence of a fading El Niño episode. Meanwhile, higher latitudes of the Northern Hemisphere were dominated by a strong negative phase of the Arctic Oscillation.
Two natural climate patterns, the Arctic Oscillation and the El Niño-Southern Oscillation, had strong influences on the patterns of unusually warm and unusually cool spots worldwide in early and late 2010.