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

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

The report, released 10 days before climate talks in Durban, South Africa, is the UN's first comprehensive review of global warming's impact on 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 approved a summary of 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 projections -- a sharp reduction in carbon emissions, a modest one, and current "business-as-usual" levels -- were reviewed in the report.

All three scenarios see a roughly similar trajectory of increased extremes up to mid-century.

But towards the end of the century the pathways diverge dramatically, with far higher and more frequent heatwaves and rainfall peaks in the worst-case scenario of 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 was 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 summarises 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.

Climate-fuelled extremes will hit the globe unevenly, it says: the 2003 heatwave that left 70,000 dead in Europe may be a template for future peaks in southern Europe and northern Africa; swathes of Africa where millions already live at hunger's edge face more drought; small island states could become unliveable due to storm surges enhanced by rising seas.

"The key message is the way the interaction of the extremes, exposure and vulnerability create disaster risk," said Chris Field, co-chair of the IPCC's Working Group II, which focuses on adaptation.

"It goes without saying that this [report] is yet another wake-up call," the European commissioner for climate action, Connie Hedegaard, said in a statement issued in Brussels.

"With all the knowledge and rational arguments in favour of urgent climate action, it is frustrating to see some governments do not show the political will to act."

"This report should leave governments in no doubt ... that climate change is, through its impact on extreme weather, already harming the lives and livelihoods of millions of people," said Bob Ward of the Grantham Research Institute on Climate Change and the Environment at the London School of Economics.