Climate Change 2001:
Working Group I: The Scientific Basis
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Figure 2.1: (a) Annual anomalies of global average land-surface air temperature (°C), 1861 to 2000, relative to 1961 to 1990 values. Bars and solid curve are from CRU (Jones et al., 2001). Values are the simple average of the anomalies for the two hemispheres. The smoothed curve was created using a 21-point binomial filter giving near decadal averages. (b) As (a) but smoothed curves only from NCDC (updated from Peterson and Vose, 1997) - thin solid curve; GISS (adapted from Hansen et al., 1999) - thick dashed curve; SHI (updated from Vinnikov et al., 1990) - thin dashed curve to 1999 only; Peterson and Vose (1997) - thin solid curve. Thick solid curve - as in (a). Two standard error uncertainties are centred on the CRU curve and are estimated using an optimum averaging method (Folland et al., 2001) and include uncertainties due to urbanisation but not due to uncertainties in thermometer exposures. The NCDC curve is the weighted average of the two hemispheres according to the area sampled, which accounts for most of the differences from the CRU curve.

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