Climate scientists have overlooked a major cause of global warming and cooling, a new study reveals today.
American researchers have discovered that the amount of water high in the atmosphere is far more influential on world temperatures than previously thought.
Although the findings do not challenge the theory of man-made global warming, they help explain why temperatures can rise and fall so dramatically from decade to decade.
The study, published in the journal Science, says a 10 per cent drop in humidity 10 miles above the Earth's surface explains why global temperatures have been stable since the start of the century, despite the rise in carbon dioxide in the atmosphere.
And a rise in water vapour in the 1980s and 90s may also explain why temperatures shot up so quickly in the previous two decades, they say.