Coolest year since 2000 but trend still shows global warming

The last 12 months have been cooler, but 2008 is still the tenth hottest year on record

James Randerson, science correspondent
guardian.co.uk, Tuesday 16 December 2008 16.00 GMT

Warming up? Climate scientists predicted 2008 would be relatively cool because of La Niña. Photograph: John McConnico/AP
The last 12 months have been the coolest since 2000, according to an analysis by Nasa's Goddard Institute for Space Studies. The meteorological year - which runs from December 2007 to November 2008 - was 0.42C warmer than the global average temperature between 1951 and 1980.
Nasa's calculations agree closely with a similar analysis by the UK Met Office which was released officially this morning, but reported by the Guardian earlier this month. According to Met Office figures for the last 11 months, the global mean temperature for 2008 is 14.3C, which is 0.14C below the average temperature for 2001-07. That makes 2008 the tenth hottest year on record.
Climate scientists had predicted that 2008 would be relatively cool compared with recent years because at the beginning of the year there was a strong La Niña event - characterised by unusually cold ocean temperatures in the equatorial Pacific Ocean.
Professor Phil Jones head of the Climate Research Unit at the University of East Anglia in Norwich said that El Niño and La Niña events have a profound impact on yearly temperature fluctuations. "The most important component of year-to-year variability in global average temperatures is the phase and amplitude of equatorial sea surface temperatures in the Pacific that lead to La Nina and El Nino events."
The influence of La Niña can be clearly seen in Nasa's analysis. Its researchers have produced a world map showing which regions of the planet were above and below their average temperature during 1951 to 1980. While much of the equatorial Pacific was 1C below average, the Antarctic Peninsula and parts of Siberia were over 2.5C above average. The Goddard Institute for Space Studies is led by the US climate scientist Prof James Hansen.
Although 2008 is cool by recent standards, it still fits with a warming trend. The 10 warmest years have occurred since 1997 and world average temperatures for the current decade are nearly 0.2C warmer than the average for the last decade.
"Human influence, particularly emission of greenhouse gases, has greatly increased the chance of having such warm years. Comparing observations with the expected response to manmade and natural drivers of climate change it is shown that global temperature is now over 0.7C warmer than if humans were not altering the climate," said Dr Peter Stott of the Met Office.