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Global warming will disrupt food supplies, slow world economic growth and may already be causing irreversible damage to nature, according to a U.N. report due this week that will put pressure on governments to act.

A 29-page draft by the Intergovernmental Panel on听Climate听Change听(IPCC) will also outline many ways to adapt to rising temperatures, more heatwaves, floods, and rising seas.

"The scientific reasoning for reducing emissions and adapting to听climate听change听is becoming far more compelling,"听, chair of the IPCC, told Reuters in听.

Scientists and more than 100 governments will meet in听听from March 25-29 to edit and approve the report. It will guide policies in the run-up to a U.N. summit in听听in 2015 meant to decide a deal to curb rising greenhouse gas emissions.

The 29-page draft projects risks such as food and water shortages and extinctions of animals and plants. Crop yields would range from unchanged to a fall of up to 2 percent a decade, compared to a world without warming, it says.

And some natural systems may face risks of "abrupt or drastic changes" that could mean irreversible shifts, such as a runaway melt of听听or a drying of the Amazon rainforest.

It said there were "early warning signs that both coral reef and Arctic systems are already experiencing irreversible regime shifts". Corals are at risk in warmer seas and the Arctic region is thawing fast.

Climate听change听will hit growth. Warming of 2.5 degrees Celsius above pre-industrial levels could mean "global aggregate economic losses between 0.2 and 2.0 percent of income", it says.

Almost 200 governments have agreed to limit warming to less than 2.0 degrees Celsius above pre-industrial times, mainly by curbing emissions from burning fossil fuels.

Temperatures have already risen by about 0.8 degrees Celsius (1.4 degrees F).听

RISING RISKS

"A wide range of impacts from听climate听change听are already happening," said听听of听听and a co-chair of the IPCC report. "Risks are much greater with more warming than less warming."

"And it doesn't require 100 percent certainty before you have creative options for moving forwards ... there are compelling adaptation options," he told Reuters by telephone.

The report points to options such as improved planning for disasters such as hurricanes or flooding, efforts to breed drought- or flood-resistant crops, measures to save water and energy or wider use of insurance.

Field said the IPCC will have to take account of thousands of comments since the draft was leaked to aclimate听sceptic's website late last year.

And the findings will be under scrutiny, especially after the previous IPCC assessment in 2007 wrongly projected that Himalayan glaciers might all melt by 2035, affecting water supplies for millions of people from听to听.

This time, a sub-chapter projects Himalayan ice will range from a 2 percent gain to a 29 percent loss by 2035. "It is virtually certain that these projections are more reliable than an earlier erroneous assessment," it says.

The study is the second part of a mammoth three-part report.

The first, in September, raised the probability that human activities, rather than natural variations, are the main cause of warming since 1950 to at least 95 percent from 90 in 2007.

But many people in big emitting nations are unconvinced.

Only 40 percent of Americans and 39 percent of Chinese view听climate听change听as a major threat, according to a Pew Research Center survey of 39 nations in 2013.

A third instalment, due in听听in mid-March, will show solutions to听climate听change听such as more renewable energy.

Reporting By听, with extra reporting by Stian Reklev in听