Global temperatures 'to decrease'

Global temperatures for 2008 will be slightly cooler than last year as a result of the cold La Nina current in the Pacific, UN meteorologists have said.

The World Meteorological Organization's secretary-general, Michel Jarraud, told the BBC it was likely that La Nina would continue into the summer.

But this year's temperatures would still be way above the average - and we would soon exceed the record year of 1998 because of global warming induced by greenhouse gases.

The WMO points out that the decade from 1998 to 2007 was the warmest on record. Since the beginning of the 20th Century, the global average surface temperature has risen by 0.74C.

While Nasa, the US space agency, cites 2005 as the warmest year, the UK's Hadley Centre lists it as second to 1998.

Researchers say the uncertainty in the observed value for any particular year is larger than these small temperature differences. What matters, they say, is the long-term upward trend.

Rises 'stalled'

La Nina and El Nino are two great natural Pacific currents whose effects are so huge they resonate round the world.

El Nino warms the planet when it happens; La Nina cools it. This year, the Pacific is in the grip of a powerful La Nina.

It has contributed to torrential rains in Australia and to some of the coldest temperatures in memory in snow-bound parts of China.

Mr Jarraud told the BBC that the effect was likely to continue into the summer, depressing temperatures globally by a fraction of a degree.

This would mean that temperatures have not risen globally since 1998 when El Nino warmed the world.

Watching trends

A minority of scientists question whether this means global warming has peaked and argue the Earth has proved more resilient to greenhouse gases than predicted.