* Rising population, development put more in harm's way
* Policymakers urged to act in next few decades
* Less emphasis on mitigation, more on cutting risk
By David Fogarty and Deborah Zabarenko A future on Earth of more extreme weather and rising seas will require better planning for natural disasters to save lives and limit deepening economic losses, the United Nations said on Wednesday in a major report on the effects of climate change.
The U.N. climate panel said all nations will be vulnerable to the expected increase in heat waves, more intense rains and floods and a probable rise in the intensity of droughts.
Aimed largely at policymakers, the report by the Intergovernmental Panel on Climate Change makes clear nations need to act now, because increasingly extreme weather is already a trend.
The need for action has become more acute as a growing human population puts more people and more assets in the path of disaster, raising economic risk, the report said. The report's title made the point: "Managing the risks of extreme events and disasters to advance climate change adaptation."
Asia was most vulnerable to potential disasters, with East Asia and the Pacific facing the highest adaptation costs.
The 594-page report, with authors from 62 countries, is the world body's most up-to-date assessment of climate change risks. Its general message is that enough is known about these risks for policymakers to start making decisions about how to deal with them.
It follows the release of the report's executive summary in November after an extensive review by scientists and government officials and is based on the work of thousands of scientific studies.
"Few countries appear to have adopted a comprehensive approach - for example, by addressing projected changes in exposure, vulnerability, and extremes," the report said. Building this into national development planning is crucial.
Global reinsurer Munich Re says that since 1980, weather-related disasters worldwide have more than tripled.
But the report sidestepped the politically divisive issue of tougher action on curbing greenhouse gas emissions blamed for stoking global warming. U.N. climate talks have become bogged down over who should take most responsibility for action.
Instead, it aimed to push adaptation to a warmer world, offering a range of strategies.
Chris Field, a lead editor of the document, acknowledged this is a change from previous IPCC reports, which largely focused on plans to mitigate climate change by limiting heat-trapping greenhouse gas emissions.
In part, Field said in a telephone interview, this is because the world's governments asked the scientists to see what could be done in the next few decades.
"BAKED INTO THE SYSTEM"
"That's a time frame where most of the climate change that will occur is already baked into the system and where even aggressive climate policies in the short term are not going to have their full effects," said Field, director of the Carnegie Institution's department of global ecology.
But the head of the U.N. panel, Rajendra Pachauri, stressed at a briefing that climate-warming emissions must be curbed: "Whatever we do, we have to adapt, of course, but also at a global level, we need to mitigate the emissions of greenhouse gases so that we ensure that these thresholds or tipping points are not exceeded."
The report looks for "low regrets" strategies that not only protect those in the path of natural disasters but also boost sustainable development. These include early warning systems, better drainage, preserving ecosystems such as mangroves, forests and water catchments, plus better building standards and overhauling health systems.
Spreading financial risk of disasters was another tool to limit the already-strained cash reserves of many poorer nations.
Micro-insurance, catastrophe bonds, national and regional risk pools could help to finance rebuilding and recovery. While take-up rates for insurance were increasing in poorer nations, the rate was still low compared with wealthier states.
Remittances, officially estimated at $325 billion in 2010, were another crucial form of finance and risk sharing, but more steps are needed to cut transaction costs.
Insurance groups said the report confirmed their experience of rising costs from climate-related disasters.
"U.S. property and casualty insurers, who are on the front line on this issue, saw catastrophe-related losses double in '11, while their net income was cut in half," Cynthia McHale, insurance program director at Ceres, an investor coalition, said in a statement.
Mark Way, head of sustainability Americas at re-insurer Swiss Re, called the report "yet another reminder of the pressing need to tackle climate risk in both the near and long term."
Nations need to do a better job in assessing people and places vulnerable to climate disasters, such as mega cities expanding further into flood plains or along low-lying coasts. Key was treating the causes, not the symptoms of vulnerability.
Risks also vary widely, from the threat of more droughts and wildfires in Australia and melting permafrost damaging buildings and roads in the Arctic to heat waves in southern Europe.
The report also said some populations are already living on the edge, given the projected increases in the magnitude or frequency of some extreme events in many regions.
"Small increases in climate extremes above thresholds or regional infrastructure 'tipping points' have the potential to result in large increases in damages to all forms of existing infrastructure nationally and to increase disaster risks," it said.
Most deaths from natural disasters -- 95 percent between 1970 and 2008 -- still occur in developing countries, the report found.
It said current spending on adaptation projects in developing countries is about $1 billion per year, a fraction of the estimated range of $70 billion to $165 billion per year on technologies to curb greenhouse gas pollution.
Yet losses from disasters were substantially higher for developing nations, with middle-income countries suffering losses of 1 percent of GDP between 2001 and 2006, compared with 0.1 percent for high-income countries.
The report's release dovetailed with an unprecedented March heat wave in the continental United States and a London conference where scientists warned the world was nearing tipping points that would make the planet irreversibly hotter.