AGU: Geophysical Research Letters

 

Editors' Highlight

Record U.S. warmth in 2006 was due to human influences

Early this year, NOAA issued a statement indicating that 2006 was the warmest in the 112-year record for the contiguous United States. However, it was unclear how much of that warming was due to human influences stemming from increasing greenhouse gases or natural influences stemming from El Niño warming of the equatorial east Pacific Ocean. To quantify the degree to which different factors contributed to this record warming, Hoerling et al. (2007) analyzed historical records of U.S. temperatures observed during past El Niño years and model simulations of sea surface temperatures under El Niño conditions, and compared these data with last year's estimates of greenhouse gas concentrations. Through statistical methods that yield estimates of temperature anomalies related to each forcing, they found that neither historical data nor model simulations revealed a U.S. warm response to El Niño. Instead, over half of the anomalous warmth in 2006 is attributed to greenhouse gas forcing, whose strength overprints natural fluctuations. The authors concluded that the record warmth was due primarily to human influences.

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