climate change development

The number of natural disasters is on the rise

While the scientific debate spirals on into ever more intransigent spirals of obfuscation, the world continues to change around us. I’ve written before about the extraordinary number of extreme weather events last year, and the record number of temperature records set. 2011 is no different so far, with serious droughts developing in some parts of the world, and the US experiencing a vicious storm season.

If it feels like there are far more hurricanes and floods these days, then your instincts are correct. The number of weather related disasters has increased dramatically in the last 30 years.

Here’s a graph from a new Oxfam report, Time’s Bitter Flood. “There is an upwards trend in the number of reported disasters” says author Steve Jennings, particularly in weather-related disasters. (Oxfam focuses on developing countries, but those interested in the US perspective might find this post interesting.)

For cynics suggesting Oxfam may have an interest in natural disasters, the data is from EM-DAT, the international disasters database. This records any reported disaster, and reports are generally filed by UN agencies. To corroborate the trend, here’s an entirely separate set of data compiled by Munich-RE. They record insurance losses and so the data is biased slightly to the developed world, but the trend is still unmistakeable.

Before we jump to conclusions, there is more than one possible explanation for this rise in the number of reported disasters. One is reporting. Perhaps our reporting is better, and more countries are on board with the EM-DAT programme, leading to more disasters. Possible, but then we would expect the number of geophysical events to have risen too – more reported earthquakes and tsunamis. The fact that only the weather related disasters are on the rise suggests the reporting bias isn’t particularly strong. (If you’re interested, the report also checks reported disasters against democracy, a free press, GDP, bureaucracy, corruption, and conflict)

Another possibility is population. EM-DAT’s definition of a disaster requires any one of the following: “ten or more people reported killed; 100 people reported affected (i.e. requiring immediate assistance in a period of emergency); declaration of a state of emergency; or a call for international assistance.” A larger population increases the likelihood of people being affected by weather events, both more often and more people affected.

Oxfam’s report analyses the data with this in mind, and finds that population is indeed a factor. “Weather-related disasters increase by 2.1 per year, compared with 3.4 per year in the non-normalised data, suggesting that increased exposure makes a considerable contribution to the increased trend in reported disasters. Nonetheless, the upwards trend is still statistically significant”.

In short, it would appear that the number of natural disasters is on the increase, and a rising population is making it more likely that people will be affected. Current climate change theory predicts a rise in the number and intensity of weather events, including floods and storms (except tropical cyclones, which the IPCC do not appear to be affected by climate change at the moment). Is that what we’re seeing here?

“It was not possible to directly analyse the effect of climate change on disaster trends” says Oxfam’s carefully worded conclusion. “However, there is insufficient evidence to exclude the possibility that climate change is increasing hazards and hence trends in reported disasters.”

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