A Misleading Claim on Climate Damages

The World Bank published a new paper last week on the economic impacts of climate change driven extreme events. It’s been getting some attention in the blogosphere. Here’s the central claim:

“Climate change is calculated to increase the damages from these five extreme events [local storms, heat waves, cold spells, floods, and droughts] by between $11 and $16 billion a year by 2100. There is little supporting evidence that climate affects deaths from these events.”

This is a stunning conclusion. It also appears to be based on a definition of “extreme” that renders it largely meaningless.

The paper itself doesn’t actually define the term “extreme event”, but it includes a few clues that something is amiss. Like this: according to Table 3, extreme heat causes on average a mere five deaths in Africa each year.

The authors take their extreme event data from the Emergency Events Database, known as EMDAT. They extrapolate from recent events to future impacts.

If you look at the publicly searchable database contents for extreme temperature events, you find that only four countries experienced deaths during the past twenty years: Algeria, Egypt, Nigeria, and South Africa. (These results don’t differentiate between heat and cold – you need to order more fine grained data for that.) That’s a bit fishy – after all, doesn’t it get hot in the rest of Africa too?

But take a look at the criteria that an event must meet to get included in the database:

For a disaster to be entered into the database at least one of the following criteria must be fulfilled:

• Ten (10) or more people reported killed.

• Hundred (100) or more people reported affected.

• Declaration of a state of emergency.

• Call for international assistance.

The key word here is reported. If a disaster isn’t reported, it doesn’t exist. What that means, in practice, is that the definition of “extreme” gets distorted. A freak heat wave that kills a few people in Canada is extreme. A freak heat wave that kills far more people in Africa is just part of life. Same for drought, flooding, and so on: By defining extreme events as discrete reported occurrences, the authors are excluding many of the most vulnerable situations. Their results may be technically solid, but they don’t appear to speak to the real concerns that serious people have about climate change.