Irma and Harvey Lay the Costs of Climate Change Denial at Trump’s Door - By Bob Ward

The president’s dismissal of scientific research is doing nothing to protect the livelihoods of ordinary Americans.

Climate change cannot be blamed for the hurricane count in any single season, nor for the occurrence of any single storm, but there are three ways in which it is making the consequences worse.

First, although the intensity of a hurricane depends on many factors, warmer seawater tends to promote stronger storms.  Average sea surface temperatures have been rising, and some parts of the North Atlantic and Gulf of Mexico are warmer than average at the moment, which is a key reason why both Harvey and Irma became so strong so quickly.

Second, a warmer atmosphere can hold more water vapor, which can result in heavier rainfall. That is true not only for hurricanes but also for weaker storms across the world. Even relatively mild tropical storms can cause great damage by dropping huge volumes of rain over one area.

Third, apart from strong winds and heavy rainfall, hurricanes cause damage through storm surges as their winds push seawater ahead of them.  Storm surges can inundate extensive low-lying coastal areas, sweeping away everything in their path.  Sea levels have been gradually rising globally, making storm surges bigger and deadlier.

Average sea surface temperatures have been rising, which is a key reason why both Harvey and Irma became so strong so quickly.

Scientists are still not sure about the other ways in which climate change may be impacting hurricanes.  The main reason Harvey created such extreme flooding around Houston was that it stalled over the city and dumped rain for several days without moving on.  We do not know if climate change played a role in creating the atmospheric conditions that made that happen.

Nor can we yet predict whether climate change will affect the number of hurricanes that occur every year.  Some studies have suggested that while numbers will drop, strengths will increase.

Also uncertain is how natural climate variability affects hurricanes.  Numbers have increased markedly in the North Atlantic since the 1990s, but this seems to be due, at least partly, to large-scale changes in ocean circulation that occur over many years or decades.

However, it is clear that the lives and livelihoods of millions of Americans will be at risk if Trump and his administration continue to deny the existence of climate change and its impact on the threat posed by hurricanes.
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Bob Ward is policy and communications director at the Grantham Research Institute on Climate Change and the Environment at the London School of Economics and Political Science

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