Geophys. Res. Lett. doi:10.1029/2009GL040736 (2009)

Climate change has left its mark on temperature extremes in the United States. Data collected by weather stations across the country from January 2000 to September 2009 reveal that there have been about twice as many record warm days as record cold days during the period, according to Gerald Meehl of the National Center for Atmospheric Research in Boulder, Colorado, and his colleagues.

The trend is strongest in the western states, where observations roughly match patterns simulated by the centre's climate-system model. For one scenario of future climate change, the model suggests that record warm days across the United States could outnumber record cold days by 20 to 1 by 2050 and by 50 to 1 by the end of the century.