Global temperatures will drop slightly this year as a result of the cooling effect of the 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.

This would mean global temperatures have not risen since 1998, prompting some to question climate change theory.

But experts say we are still clearly in a long-term warming trend - and they forecast a new record high temperature within five years.

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.

 Source : BBC Science