By Alister Doyle
OSLO (Reuters) - Global warming poses a mounting threat to health, economic growth, crops and water supplies, according to a draft report by top scientists that puts unprecedented emphasis on the risks of a changing climate.
A leaked 29-page draft by the U.N. Intergovernmental Panel on Climate Change (IPCC), about the impacts of rising temperatures and due for release in March 2014, mentions "risk" 139 times against just 41 in its last assessment in 2007.
The increased stress on risk may make the case for cutting greenhouse gas emissions clearer both to policymakers and the public by making it sound like an insurance policy for the planet, analysts say.
Many governments, meeting in Warsaw from November 11-22 for U.N. talks on climate change, have long pleaded for greater scientific certainty before making billion-dollar investments in everything from flood barriers to renewable energies.
But certainty is elusive in climate science, as it is in predicting anything from the weather to Wall Street.
"The IPCC has transitioned to what I consider to be a full and rich recognition that the climate change problem is about managing risk," Christopher Field, co-chair of the IPCC group preparing the report, told Reuters.
The report, posted on a climate skeptical website "nofrakkingconsensus" on November 1, resembles a previous draft that warns that parts of society and nature are more vulnerable than expected to climate change.
Field, a professor at Stanford University, also said there was more certainty about many aspects of climate change than in 2007. He cautioned the draft was subject to change in editing.
It says, for instance, that a rise of temperatures of more than 2.5 degrees Celsius (4.5 Fahrenheit) above pre-industrial times could lead to economic losses of between 0.2 and 2.0 percent of global income.
It also says that warming will exacerbate threats to health, damage yields of major crops in many areas and lead to more floods. It could also exacerbate poverty and economic shocks that are root causes of violent conflicts.
"Responding to climate-related risks involves making decisions and taking actions in the face of continuing uncertainty about the extent of climate change and the severity of impacts in a changing world," the draft says.
The panel's credibility is under extra scrutiny, for its last report in 2007 wrongly exaggerated the melt of Himalayan glaciers. Several reviews said that this error, however, did not undermine the key findings in 2007.
James Painter, of the Reuters Institute for the Study of Journalism at Oxford University, said that the focus on risk may make the panel's message clearer.
"More risk language helps to shift the public debate away from the idea that decisions should be delayed until absolute certainty is obtained - something that may never be achieved."
He said politicians and businesses were used to making decisions based on risks. And many people insure their homes against fire even though the risks of a blaze are small.
Field said the report tries to capture a wide range of risks, including highly unlikely events that might have a major impact. "That's the way risk is generally formulated if you are an insurance company or figuring out an anti-terrorism policy."
The report is the second in a four-part IPCC assessment meant to guide governments that have promised to agree a pact in 2015 to slow climate change. The first, in September, raised the probability that most global warming is man-made to at least 95 percent from 90 in 2007.
(Editing by Mark Heinrich)