GLOBAL: Scientists find water vapour has significant effect on global temperatures (02/02/10)
National Oceanic and Atmospheric Administration (NOAA) scientists have found that the amount of water vapour high in the earth’s atmosphere has a far greater influence on global temperatures than previously thought.
The research, published in the journal Science, says that a 10% drop in humidity ten miles (16 km) above the earth’s surface explains why global temperatures have remained stable since the start of the new millennium despite an increase in carbon dioxide in the atmosphere.
An increase in water vapour in the 1980s and 1990s may also explain why temperatures rose so quickly then, the scientists said.
Water vapour has long been recognised as a key greenhouse gas, absorbing heat from the sun that would otherwise be reflected back into space. However, most computer climate prediction models focus on water vapour levels in the atmosphere near the surface.
The changes that have now been detected have taken place in the stratosphere, between eight and 30 miles (12.8 and 48 km) above the earth’s surface, although the reason for the rise and fall in vapour levels is still unknown. The study suggests that whatever the mechanism, the drop in water vapour has caused surface temperatures to rise 25% more slowly than they would have done otherwise.
NOAA senior scientist and primary study author Susan Solomon is quoted as saying: ‘Current climate models do a remarkable job on water vapour near the surface. But this is different – it’s a thin wedge of the upper atmosphere that packs a wallop from one decade to the next in a way we didn’t expect.’
Lis Stedman
