Over the last half-century, global warming has led to changes in climate extremes such as heat waves, record high temperatures and in many regions, heavy precipitation. That's the conclusion of a new report by the Intergovernmental Panel on Climate Change. The group, founded by the United Nations in 1988, warns that nations across the globe must take steps to mitigate such disaster.

Extreme weather cut a swath across the world in 2011. For Bill Wing, it began a year ago on New Year's Day as he surveyed the damage from a tornado that touched down in Cincinnati, Arkansas.

"It sounded like a freight train coming," said Wing. "You could feel the wind was moving and the shaking, more like an earthquake for us."

That tornado was among 1600 that crisscrossed the United States last year. That same pattern of extreme weather was experienced across the globe. In Thailand, rainfall was 80 percent more than the seasonal average and the capital city was deluged. The year before, Russia experienced its hottest summer in 500 years.

"It's very clear that heat waves are on the increase both in terms of numbers and duration," said Rajendra Pachauri. "Another important finding is the fact that extreme precipitation events are on the increase."

IPCC Chairman Rajendra Pachauri says the panel's report strongly suggests that this trend will continue as temperatures rise.

"And, in fact, if you make projections for the future, you'll find that in the case of heat waves, those heat waves which are currently taking place once in 20 years will by the end of the century take place once in two years," he said.

While no evidence connects global warming with specific local weather events, Chairman Pachauri says warmer temperatures, boosted by CO2 and other gas emissions from the burning of fossil fuels, will trigger more intense droughts, heavier rainfall and stronger storms.

"Basically we have to stabilize the concentration of these greenhouse gases, which includes carbon dioxide as the most dominant gas in the atmosphere, such that, we can stabilize the climate of this planet and thereby minimize or delay or avoid some of the worst impacts that are going to take place in the future," said Pachauri.

Extreme weather disasters are costly, on average $80 billion a year. While the IPCC study makes clear that no country is immune, Pachauri notes that poorer nations will pay a higher price - in dollars and deaths - because they are least able to respond. He adds, the options are clear:

"We need to adapt to the impacts of climate change, in particular, extreme events and disasters related to climate change," he said. "And, we will have to mitigate, because it is also very clear that there are certain thresholds and points both in social as well as in natural systems where the resilience of societies will be exceeded in such a way that there will be a severe challenge in terms of adaptation. So, we have to mitigate."

The 594-page IPCC report is the work of 220 authors from 62 countries. It cites thousands of scientific studies. Enough is known, the editors say, to make good decisions about how to manage risks of climate-related disasters.