Climate Science

What Have We Done?

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Science  10 Oct 2008:
Vol. 322, Issue 5899, pp. 167
DOI: 10.1126/science.322.5899.167b

Global climate is warming rapidly, and has been for more than 150 years, since around the start of the Industrial Revolution. Climate models suggest that most of the rise is due to greenhouse gas emissions, but the accuracy of the models is not entirely certain, and there have been numerous high-profile disagreements about their credibility. An alternate way to estimate the magnitude of human influence on global temperatures is to look at the observational record. Lean and Rind found that only four factors—ENSO (El Niño-Southern Oscillation), volcanic activity, solar activity, and anthropogenic forcing by greenhouse gases—are required to explain 76% of the variance in the temperature records. Furthermore 90% or more of the warming trend of the past 100 years can be explained by invoking anthropogenic effects, and solar forcing can explain a negligible percentage of the rise in temperature over the past 25 years. Finally, the zonal temperature response to natural and anthropogenic forcing does not increase rapidly with latitude from mid- to high latitudes, as it does in models, and anthropogenic warming effects are more pronounced in the latitudes between 45°S and 50°N than at higher latitudes. — HJS

Geophys. Res. Lett. 35, L18701 (2008).

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