The betting is that 2010 will be the hottest year on record. But understanding how the planet’s temperature changes is still a challenge to science

IT MAY seem implausible at the moment, as northern Europe, Asia and parts of America shiver in the snow, but 2010 may well turn out as the hottest year on record. Those who doubt that greenhouse gases are quite the problem they have been cracked up to be by most of the world’s climatologists have taken comfort from the fact that the Hadley Centre, part of Britain’s Meteorological Office, reckons the warmest year since records began was 1998 (see chart 1). Twelve years without a new record would, the sceptics reckon, be rather a large lull in what is supposed to be a rising trend. Computer modelling by the Met Office, though, gives odds-on chances of the lull being broken.

The fact that no record high happened in the 2000s does not mean that there was no warming over the decade—trends at scales coarser than the annual continued to point upwards, and other authorities suggest there have been record years during the period. Nor was the length of time without an annual record exceptional. Models simulating centuries of warming normally have the occasional decade in which no rise in surface temperatures is observed. This is because heat can be stored in other parts of the system, such as the oceans, for a time, and thus not show up on meteorologists’ thermometers. …