Climate change drives extreme weather: UN

Man-made climate change has already boosted heatwaves and flood-provoking rainfall and is likely to contribute to future natural disasters, according to UN scientists.

But the human and economic toll of these extreme weather events will depend as much on the measures taken to protect populations as the violence of Nature's outbursts, it warned.

The report, released only days before the start of climate talks in Durban, South Africa, is the UN's first comprehensive review of global warming's impact on disaster-provoking weather extremes, and how best to manage them.

"We can actually attribute the increase of hot days in the past few years to an increase in greenhouse gases," said Thomas Stocker, co-chair of the Intergovernmental Panel on Climate Change (IPCC), which published the report at a meeting in the Ugandan capital, Kampala.

"And it is virtually certain that increases in the frequency and magnitude of warm daily temperature extremes, and decreases in cold extremes, will occur in the 21st century," he said at a press conference.

"Heavy precipitation will become more frequent in many regions of the world," he added.

Heat and rain extremes under three carbon pollution scenarios -- ranging from a sharp reduction in emissions to business-as-usual -- were reviewed in the report.

All three increase along a similar trajectory up to 2050.

But towards the end of the century these pathways diverge dramatically, with far higher and more frequent heatwaves and rainfall peaks in a world saturated with greenhouse gases.

For the high-emission scenario -- the path the world is on now -- one-in-20-year heat peaks would occur every five years by about 2050, and every year or two by the end of the century. Precipitation extremes increase in a similar fashion, the report showed.

Qin Dahe, also an IPCC co-chair, said the panel is likewise "more confident" that climate change is boosting glacier retreat, a major concern for nations in Asia and South America dependent on glaciers for water.

But for other extreme weather events such as cyclones, scientists are still unable to pin down the impact of climate change, due to lack of data and the "inherent variability and variations in the climate system," Stocker said.

"Uncertainty cuts both ways. Events could be more severe and more frequent than projections suggest, or vice versa."

Some studies have suggested that warmer air and sea surface temperatures combined with greater moisture in the air will intensify tropical storms.

The 20-page document released Friday summarizes the conclusions of an underlying 800-page report, three years in the making, that reviews thousands of recent peer-reviewed scientific articles.

It was written by some 200 scientists, and approved this week by the 194-nation IPCC, which gathers government representatives as well as experts.