U.N.: Wilder weather on the way

The threat of heat waves and heavy precipitation are becoming especially severe, warns the Intergovernmental Panel on Climate Change.

Fri, Nov 18 2011 at 1:36 PM EST

STORM SCOURGE: Hurricane Katrina roars toward New Orleans in this satellite photo, taken on Aug. 28, 2005. (Photo: U.S. National Oceanic and Atmospheric Administration)

People around the planet should prepare for "unprecedented extreme weather," according to a report released Friday by top international scientists and disaster experts. Earth's recent wild weather is likely just a sneak peek, the report warns, as rising global temperatures cook the oceans and atmosphere into a frenzy.

"We need to be worried," one of the study's lead authors tells the Associated Press. "And our response needs to anticipate disasters and reduce risk before they happen rather than wait until after they happen and clean up afterward. ... Risk has already increased dramatically."

This dire outlook comes via the U.N. Intergovernmental Panel on Climate Change, a Nobel Prize-winning research group that issues periodic reports on global warming. The IPCC's next big report is due in 2014, but a panel meeting in Uganda this week decided the threat of extreme weather warrants a warning now. If greenhouse gas emissions keep rising, the IPCC says temperatures — and weather — could quickly spiral out of control.

"For the high-emissions scenario, it is likely that the frequency of hot days will increase by a factor of 10 in most regions of the world," says the IPCC's Thomas Stocker. "Likewise, heavy precipitation will occur more often, and the wind speed of tropical cyclones will increase while their number will likely remain constant or decrease."

Scientists avoid blaming specific storms on climate trends, but the broader link between weather and warming has been discussed for years — especially after the horrific 2005 hurricane season. It has become an increasingly common topic of debate over the last two years, as blizzards battered North America and Europe, wildfire and droughts ravaged Russia and Somalia, floods inundated Pakistan and Thailand, and tornadoes leveled U.S. cities from Missouri to Massachusetts.

Governments are still fighting over details in the new study, since its "summary for policymakers" (PDF) must be ratified by every participating nation, the Guardian reports. But when the full special report comes out in February, it's expected to add major clout to the theory that manmade emissions are raising the risk of extreme weather events, namely heat waves, droughts and rainfall.

Climate science has grown more sophisticated in recent years, the report's authors explain, letting them link the frequency of many severe weather events to climate change with more confidence than before. They are now "virtually certain" that heat waves are becoming longer and hotter, for example, and they predict heat waves that used to strike once every 20 years will occur every five years by 2050, and could occur every other year by 2100. There's also a two-in-three chance that heavy rainfall will increase, the report adds, in the tropics as well as mid-latitude and northern regions.

Still, just as temperatures don't increase uniformly across the planet, the threat of extreme weather isn't the same everywhere, IPCC Chairman Rajendra Pachauri points outs in a press release. The new report, he explains, also aims to help communities customize their plans for adapting to the various ways severe weather affects them.

"This summary for policymakers provides insights into how disaster risk management and adaptation may assist vulnerable communities to better cope with a changing climate in a world of inequalities," Pachauri says. "It also underlines the complexity and the diversity of factors that are shaping human vulnerability to extremes — why for some communities and countries these can become disasters whereas for others they can be less severe."

Friday's summary doesn't identify which communities or countries will be hardest hit, but it's well-known that low-lying islands, coastal areas and mountainous regions are especially at risk from heavy rain, cyclones, floods and mudslides. Poor regions of Southeast Asia, Africa and South America are often highlighted as danger zones, but wealthier regions aren't immune from severe weather — as seen during this year's historic flooding in Australia and tornado outbreaks in the U.S. Overall, global financial losses to weather disasters are already up to $200 billion per year, the report says.

While the IPCC irons out the details of its severe weather warning, here are some U.S. forecasts produced by the National Climatic Data Center: