Figure 2.8: Smoothed annual
anomalies of global combined land-surface air and sea surface temperatures (°C),
1861 to 2000, relative to 1961 to 1990, and twice their standard errors. The smoothed
curves and shaded areas were created using a 21-point binomial filter giving near-decadal
averages, with appropriate errors. Optimally averaged anomalies and uncertainties
(Folland et al., 2001) – solid curve and dark shading; standard area weighted
anomalies and uncertainties (adapted from Jones et al., 1997b, 2001) – dashed
curve and light shading. Note that uncertainties decrease after 1941 due to the
cessation of uncertainties due to bias corrections in sea surface temperature.
On the other hand, uncertainties due to urbanisation of the land component, assessed
as zero in 1900, continue to increase after 1941 to a maximum in 2000.