Climate Change 2001:
Working Group I: The Scientific Basis
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Figure 2.7: Smoothed annual anomalies of combined land-surface air and sea surface temperatures (°C), 1861 to 2000, relative to 1961 to 1990, for (a) Northern Hemisphere; (b) Southern Hemisphere; and (c) Globe. The smoothed curves were created using a 21-point binomial filter giving near-decadal averages. Optimally averaged anomalies (Folland et al., 2001) solid curves; standard area weighted anomalies (adapted from Jones et al., 2001) dashed curves. Also shown are the unsmoothed optimum averages red bars, and twice their standard errors width denoted by black I. Note that optimum averages for the Southern Hemisphere are a little warmer before 1940, when the data are sparse, than the area-weighted averages. However, the two types of averaging give similar resoults in the Northern Hemisphere.

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