Warming begins to hit rain

A study has yielded the first confirmation that global warming is already affecting world’s rainfall patterns, bringing more precipitation to northern Europe, Canada and northern Russia but less to swathes of sub-Saharan Africa, southern India and Southeast Asia. The changes "may have already had significant effects on ecosystems, agriculture and human regions that are sensitive to changes in precipitation, such as the Sahel," warns the paper, released on Monday by Nature, the British science journal.

Scientists have long said that global warming is bound to interfere with snow and rainfall patterns, because air and sea temperatures and sea-level atmospheric pressure — the underlying forces behind these patterns — are already changing. But, until now, evidence for declaring that the interference is already happening existed anecdotally or in computer models, rather than from observation.

One problem for researchers has been a lack of accurate, long-term rainfall data from around the world that would enable them to distinguish between regional or cyclical shifts in rainfall. Francis Zwiers, a scientists with Environment Canada, Toronto, used two data-sets of global rainfall pattern beginning, conservatively, in 1925 and ending in 1999. They compared these figures with 14 powerful computer models that simulate the world’s climate system, and found a close fit.