At a talk given last month at the American Geophysical Union meeting in San Francisco, Mark Bove of Munich Re insurance company examined trends in both damages and number of natural disasters since 1980. These numbers have shown significant increases since 1980. After we take out the increase in disasters reported due to an increasing population, greater wealth, and more advanced communications, is there a trend due to climate change?

One way to check is to compare natural disasters due to geophysical events--earthquakes, tsunamis, and volcanic eruptions--to weather-related disasters. Geophysical disasters should remain relatively constant in number in a changing climate (unless sea level rise is occurring so rapidly that it is causing significant changes in stress on earthquake faults, something that is theoretically possible, but has not yet been observed.) If we then look at trends in the number of geophysical disasters versus weather-related disasters reported, it should give us an idea of how much of the recent increase in weather-related disasters may be due to climate change.

Between 1980 and 2010, geophysical disasters increased by about a factor of 1.5, while weather-related disasters increased by a factor of 2.7 to 3.5 (Figure 3.) Bove stated that he thought weather-related disasters were likely subject to a higher increase in reporting rate than geophysical disasters, but not enough to account for the huge difference. Climate change was the likely reason for a large portion of the increase in weather-related disasters in recent years, he argued. His talk concluded, "there is quite some probability that natural catastrophe losses are driven already by human-caused climate change."

However, this conclusion is controversial. A 2010 paper in the Bulletin of the American Meteorological Society by Netherlands researcher Laurens Bouwer titled, "Have disaster losses increased due to anthropogenic climate change?", looked at 22 disaster loss studies world-wide, published between 2011 and 2010. All of the studies showed an increase in damages from weather-related disasters in recent decades.

Fourteen of the 22 studies concluded that there were no trends in damage after correcting for increases in wealth and population, while eight of the studies did find upward trends even after such corrections, implying that climate change could be responsible for the increased disaster losses. In all 22 studies, increases in wealth and population were the "most important drivers for growing disaster losses." Looking at disasters losses to make an argument that climate change is affecting our weather is difficult, due to the rarity of extreme events, and the changes in wealth and population that also affect disaster losses. We are better off looking at how the atmosphere, oceans, and glaciers are changing to find evidence of climate change.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2009


Figure 3. The number of natural disasters reported has increased markedly worldwide since 1980, particularly for weather-related disasters. Image credit: Munich Re.