Ships and buoys made global warming look slower

New Scientist: Claims that global warming has slowed down over the past decade were partly based on faulty data. Instead, the rate of global warming was underestimated because of a new way of measuring sea-surface temperatures, suggests a new study.

Since the 1970s average global temperatures have risen by 0.16 °C per decade, but over the past decade they seemed to rise by only 0.09 °C, an apparent slowdown of 0.07 °C. John Kennedy and colleagues at the UK Met Office have now found that the real slowdown was smaller.

Over the past decade, sea-surface temperature has mostly been measured by thermometers on buoys, whereas previously it was measured aboard ships. Ship measurements tend to be too high because the water warms up as it is taken on board. So although the newer buoy measurements are more accurate, the switch in method has erroneously shown sea-surface temperatures appearing to level off.

"Compared with ships, buoys show cooler temperatures," says Vicky Pope at the Met Office. "You have to be careful of false signals." Kennedy says the underestimation of the change in sea-surface temperature could account for up to 0.03 °C of the apparent slowdown in global temperatures. The correction could mean that 2010 will be the warmest year on record, surpassing 1998 and 2005…