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Detection of human influence on sea-level pressure


Greenhouse gases and tropospheric sulphate aerosols—the main human influences on climate—have been shown to have had a detectable effect on surface air temperature1,2,3, the temperature of the free troposphere and stratosphere2,4 and ocean temperature5,6. Nevertheless, the question remains as to whether human influence is detectable in any variable other than temperature. Here we detect an influence of anthropogenic greenhouse gases and sulphate aerosols in observations of winter sea-level pressure (December to February), using combined simulations from four climate models. We find increases in sea-level pressure over the subtropical North Atlantic Ocean, southern Europe and North Africa, and decreases in the polar regions and the North Pacific Ocean, in response to human influence. Our analysis also indicates that the climate models substantially underestimate the magnitude of the sea-level pressure response. This discrepancy suggests that the upward trend in the North Atlantic Oscillation index7 (corresponding to strengthened westerlies in the North Atlantic region), as simulated in a number of global warming scenarios8,9,10, may be too small, leading to an underestimation of the impacts of anthropogenic climate change on European climate.

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Figure 1: Observed and simulated sea-level pressure trends.
Figure 2: Regression coefficients, β, of observed sea-level pressure changes against changes simulated in response to greenhouse gas and sulphate aerosol increases.

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We thank R. Allan and J. Arnott for supplying the HadSLP data set, and M. Allen for allowing us to use his optimal detection code. We thank NSERC and CFCAS for CLIVAR funding. A.J.W. is grateful for support from the Killam Foundation and the Canada Research Chair Program, and P.A.S. is grateful for support from the Department for Environment, Food and Rural Affairs.

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Correspondence to Nathan P. Gillett.

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Gillett, N., Zwiers, F., Weaver, A. et al. Detection of human influence on sea-level pressure. Nature 422, 292–294 (2003).

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