An especially cold year in North America in 2008 led some members of the public and the media to question the scientific consensus on human-induced global warming. In addition, the cool global temperatures during the past decade may appear to contrast with the warming expected due to human influence.
To clarify the roles of human influence and natural climate variability, Perlwitz et al. used observed temperature data and a suite of climate model simulations to analyze factors contributing to the 2008 North American temperature conditions.
The researchers found that the anthropogenic forcing in 2008 did contribute to temperatures warmer than would otherwise have occurred but that those human-induced effects were overwhelmed by a particularly strong bout of natural cooling. The authors determined that the North American cooling likely resulted from a widespread natural coolness in the tropical and northeastern Pacific Ocean.
The study implies that the abnormally cool 2008 is not likely part of a prolonged cooling trend and that general warming trends are likely to continue.
The research is published in Geophysical Research Letters. Authors include Judith Perlwitz, Jon Eischeid, and Taiyi Xu: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA, and Earth System Research Laboratory, NOAA, Boulder, Colorado, USA; Martin Hoerling: Earth System Research Laboratory, NOAA, Boulder, Colorado, USA; and Arun Kumar: Climate Prediction Center, NOAA, Camp Springs, Maryland, USA
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