By Quirin Schiermeier of Nature magazine

Natural disasters around the world last year caused a record $380 billion in economic losses. That's more than twice the tally for 2010, and about $115 billion more than in the previous record year of 2005, according to a report from Munich Re, a reinsurance group in Germany. But other work emphasizes that it is too soon to blame the economic devastation on climate change.

Almost two-thirds of 2011's exceptionally high costs are attributable to two disasters unrelated to climate and weather: the magnitude-9.0 earthquake and tsunami that hit Japan in March, and February's comparatively small but unusually destructive magnitude-6.3 quake in New Zealand.

And the long-term rise in the costs of global disasters is probably due mainly to socio-economic changes, such as population growth and development in vulnerable regions. That conclusion is backed up by a forthcoming study--supported by Munich Re--by economists Fabian Barthel and Eric Neumayer at the London School of Economics. Their analysis of events worldwide between 1990 and 2008 concludes that "the accumulation of wealth in disaster-prone areas is and will always remain by far the most important driver of future economic disaster damage" (F. Barthel and E. Neumayer Climatic Change; in the press). Any major weather event hitting densely populated areas now causes huge losses because the value of the infrastructure has increased tremendously, they note, adding that if the 1926 Great Miami hurricane happened today, for example, it would cause much more damage than it did at the time.

However, weather-related events are generally on the rise. Thanks to a relatively quiet Atlantic hurricane season, damage caused by extreme weather was actually lower in 2011 than in four of the previous five years. But weather accounted for about 90% of the year's 820 recorded natural disasters, which caused at least 27,000 deaths. These disasters include flooding in Thailand, a series of tornadoes that hit the United States Midwest and southern states last spring, and storms and extreme rainfall over parts of the Mediterranean in November.

Since 1980, the report notes, the number of severe floods has almost tripled, and storms have nearly doubled, which insurance experts link, in part, to the impact of climate change (see `Catastrophe count'). "It would not seem plausible that climate change doesn't play a role in the substantial rise in weather-related disasters," says Ernst Rauch, head of Munich Re's Corporate Climate Centre.

Climate scientists believe that the frequency and severity of extreme-weather events will increase as temperatures continue to rise. The summary of a report published in November by the Intergovernmental Panel on Climate Change supports that view and warns that some areas could even become "increasingly marginal as places to live in".

But attempts to attribute specific events to global warming are in their infancy (see Nature 477, 148-149; 2011). "Disasters are a tempting image for advocacy, but the science is just not there to support strong claims," says Roger Pielke Jr, a climate-policy researcher at the University of Colorado in Boulder. "We cannot yet attribute increasing dollar losses to human-caused climate change. Maybe we will one day, but not at present."

This article is reproduced with permission from the magazine Nature. The article was first published on January 10, 2012.