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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L17704, doi:10.1029/2007GL030643, 2007

Explaining the record US warmth of 2006

Martin Hoerling

NOAA Earth System Research Laboratory, Boulder, Colorado, USA


Jon Eischeid

NOAA Earth System Research Laboratory, Boulder, Colorado, USA


Xiaowei Quan

NOAA Earth System Research Laboratory, Boulder, Colorado, USA


Taiyi Xu

NOAA Earth System Research Laboratory, Boulder, Colorado, USA


Abstract

This study explores origins for record setting 2006 temperatures over the conterminous United States. The efficacy of two mechanisms is quantified; one associated with sea surface temperatures (SSTs) in the equatorial Pacific related to El Niño, and the other associated with increased greenhouse gas concentrations. We use historical records of US temperatures observed during past El Niños, model simulations subjected to El Niño SST conditions and to projections of the 2006 greenhouse gas concentrations. We use ensemble methods to yield probabilistic estimates of temperature anomalies related to each forcing. Neither historical data nor model simulations reveal a US warm response to El Niño indicating it was not a factor in elevating US temperatures. Instead, over half of the anomalous warmth in 2006 is attributed to greenhouse gas forcing, whose strength now exceeds the standard deviation of natural fluctuations. We conclude that the record warmth was primarily due to human influences.

Received 10 May 2007; accepted 18 July 2007; published 5 September 2007.

Keywords: greenhouse gas forcing; attribution; El Niño.

Index Terms: 1616 Global Change: Climate variability (1635, 3305, 3309, 4215, 4513); 1620 Global Change: Climate dynamics (0429, 3309); 1635 Global Change: Oceans (1616, 3305, 4215, 4513); 1637 Global Change: Regional climate change.

Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 218887 bytes)

Citation: Hoerling, M., J. Eischeid, X. Quan, and T. Xu (2007), Explaining the record US warmth of 2006, Geophys. Res. Lett., 34, L17704, doi:10.1029/2007GL030643.