Global and regional climate in 2010

The global average temperature near the surface of the earth calculated from the third version of the Hadley Centre and Climatic Research Unit’s (HadCRUT3) (Brohan et al., 2006) data set in 2010 was 0.50 ± 0.09 degC above the 1961–1990 average (Figure 1(a)). 2010 is nominally the second warmest year in HadCRUT3, but the uncertainties are such that it is statistically indistinguishable from any of the seven warmest years. The largest component of the uncertainty in recent years arises from large areas of missing data at high latitudes where there are few observing stations. The National Climate Data Center (NCDC) and the National Aeronautics and Space Administration’s Goddard Institute for Space Studies (NASA GISS) data sets estimate temperature anomalies in these regions, with GISS extrapolating temperatures the most extensively. The Arctic has warmed much faster than the rest of the globe and so GISS has reported higher global average temperatures than NCDC and HadCRUT3 in recent years. The analyses produced by NASA GISS (Hansen et al., 2010) and NCDC (Smith et al., 2008) rank 2010 as the joint warmest year. The warmth of 2010 was due in part to the El Nino that developed in 2009: El Nino events normally lead to a rise in global average temperature. The effects of El Nino on global temperature typically lag temperature changes in the tropical Pacific (Figure 2) by a few months (Trenberth et al., 2002). The recent El Nino reached its peak strength in December 2009 with an average sea-surface temperature anomaly in the Nino 3 region (150°–90°W, 5°S–5°N, Figure 2) of around +1.5 degC. There was a rapid transition from El Nino to La Nina conditions in 2010 and