Report: Climate change behind rise in weather disasters

• Reinsurer Munich Re reports climate change behind rise in disasters
• Weather disasters in North America are among the worst
• Other experts take issue with Munich Re's findings

The number of natural disasters per year has been rising dramatically on all continents since 1980, but the trend is steepest for North America where countries have been battered by hurricanes, tornadoes, floods, searing heat and drought, a new report says.

The study being released today by Munich Re, the world's largest reinsurance firm, sees climate change driving the increase and predicts those influences will continue in years ahead, though a number of experts question that conclusion.

Whatever the causes, the report shows that if you thought the weather has been getting worse, you're right.

The report finds that weather disasters in North America are among the worst and most volatile in the world: "North America is the continent with the largest increases in disasters," says Munich Re's Peter Hoppe.

The report focuses on weather disasters since 1980 in the USA, Canada, Puerto Rico and the U.S. Virgin Islands.

Hoppe says this report represents the first finding of a climate change "footprint" in the data from natural catastrophes.

Some of the report's findings:

-- The intensities of certain weather events in North America are among the highest in the world, and the risks associated with them are changing faster than anywhere else.

-- The second costliest year of the study period, 2011, was dominated by strong storms. Insured losses in the U.S. due to thunderstorms alone was the highest on record at an estimated $26 billion, more than double the previous thunderstorm record set in 2010.

-- Insured losses from disasters averaged $9 billion a year in the 1980s. By the 2000s, the average soared to $36 billion per year.

Global warming combined with natural cycles such as the El Niño or La Niña phenomena also intensify the risk of severe weather. "This will result in higher natural peril losses and affect not only the onset of heat waves, droughts and thunderstorms but also, in the long term, the intensity of tropical cyclones," the report finds.

Reinsurers such as Munich Re offer backup policies to companies writing primary insurance policies. Reinsurance helps spread risk, so the system can handle large losses from natural disasters.

"We see some trends that are linked with changes in atmospheric conditions, such as more water content in the atmosphere due to global warming," Hoppe says. Additional water vapor in the atmosphere is the fuel for the big storms, he says.

However, other experts take issue with Munich Re's findings. "Thirty years is not an appropriate length of time for a climate analysis, much less finding causal factors like climate change," says Roger Pielke, a professor of environmental studies at the University of Colorado.

Another reinsurer, Axa, isn't quite sure of the link either: "While a clear upward trend arises from the figure with respect to the number of reported natural events, the attribution of this rise to a climate change signal should be investigated very cautiously," the French company says in its report "Climate Risks" released earlier this month.

Atmospheric scientist Clifford Mass of the University of Washington also has a problem with Munich Re's findings, saying that once the data are adjusted for population there is no recent upward trend in tornado or hurricane damages. Also, he adds that there is no evidence that global warming is causing more extreme weather in the USA.

Hoppe, however, says that even if we adjust for population spread and increased property values, Munich Re still says there were significant increases in the costs of weather disasters over the past few years.