Hurricane Harvey and Climate Change

Did climate change cause Hurricane Harvey? That’s not a good question and it can’t be answered satisfactorily. Better to ask “Did climate change make Hurricane Harvey more severe?” The answer to this question is “Yes”.  Here’s the explanation.

Water Temperature. Global warming heats the earth’s oceans. The water in the Gulf of Mexico is about 1.5 degrees Celsius warmer than it was only a few decades ago. Warm water is the fuel that feeds energy into a hurricane. Usually storms lose energy as they approach the coast as they churn up cooler deeper water, but the warmer water in the Gulf caused Harvey to gain energy as it approached the coast. By the time it made landfall it was upgraded from a tropical storm to a Category 4 hurricane.

Air Temperature. Global warming heats the earth’s atmosphere. So far the average temperature has risen almost 1 degree Celsius. Warmer air can hold more water vapour than colder air. More humid air with more moisture results in storms with more rain. There’s even a 150 year old equation called the Clausius–Clapeyron equation that can calculate how much more. In this case it’s from 3% to 5% more moisture.

Sea Level. Global warming causes sea level to rise for 2 reasons. Warmer water takes up more space, and melting ice caps add more liquid to the oceans. So far the seas have risen only about 50 cm. When the sea is higher then a storm surge associated with a hurricane causes flooding from the ocean. This was important for Sandy and Katrina but was not a factor with Harvey in Houston.

Harvey Stalled. Harvey stalled over Houston instead of just moving quickly on resulting in more and more rainfall because of the duration of the storm in one place. The link between this stalling and climate change is less certain but there is mounting evidence for it.

Infrastructure. Houston is a very populous city built on a flood plain that is largely paved over, so when rain falls it stays on the surface and causes flooding. Stormwater management systems were inadequate to deal with the volume of rain that fell. The human and the economic cost are evident as we saw with Sandy and Katrina and will certainly see again with Harvey.

I like to think of things in terms of analogies and I like the analogy that weather with climate change is like Barry Bonds hitting home runs after taking steroids. Asking if climate change caused any particular event is like asking if Barry Bonds’ steroid use caused any specific home run. You can say that some of his home runs would not have cleared the fence without the steroids but not any particular one. In a similar way we can’t say that climate change caused hurricane Harvey but there is lots of strong evidence that climate change made the storm more severe than it would have been without climate change.

Climate scientists have been predicting stronger and more frequent storms for some time and they now predict that this trend will continue at an increasingly alarming pace as the world continues to heat up.

Finally, I would like to draw your attention to this more controversial article by George Monbiot from the Guardian. In it he bemoans the fact that the media censors itself about climate change, especially when it comes to linking it to an extreme weather disaster like the Fort McMurray wildfire or Hurricanes Sandy and Harvey. It is seen as too political to talk about climate change when the event is unfolding, but then we miss our chance as people stop paying attention once the smoke clears or the flood waters recede. Here is a quote from his article.

I believe it is the silence that’s political. To report the storm as if it were an entirely natural phenomenon, like last week’s eclipse of the sun, is to take a position. By failing to make the obvious link and talk about climate breakdown, media organisations ensure our greatest challenge goes unanswered. They help push the world towards catastrophe.

So, what are we to do? It is our obligation to continue to raise public awareness of the seriousness of climate change and to continue to work on the political level to enact policies that will mitigate the damages.

For further reading on the relationship between Hurricane Harvey and climate change, please refer to the articles below.


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