Is there a link between the storm and climate change?

Almost certainly, according to a statement issued by the World Meteorological Organization on Tuesday. “Climate change means that when we do have an event like Harvey, the rainfall amounts are likely to be higher than they would have been otherwise,” the UN organisation’s spokeswoman Clare Nullis told a conference. Nobody is arguing that climate change caused the storm, but it is likely to have made it much worse.

How did it make it worse?

Warmer seas evaporate more quickly. Warmer air holds more water vapour. So, as temperatures rise around the world, the skies store more moisture and dump it more intensely. The US National Weather Service has had to introduce a new colour on its graphs to deal with the volume of precipitation. Harvey surpassed the previous US record for rainfall from a tropical system, as 49.2 inches was recorded at Mary’s Creek at Winding Road in Southeast Houston, at 9.20am on Tuesday.

Is this speculation or science?

There is a proven link – known as the Clausius-Clapeyron equation – that shows that for every half a degree celsius in warming, there is about a 3% increase in atmospheric moisture content. This was a factor in Texas. The surface temperature in the Gulf of Mexico is currently more than half a degree celsius higher than the recent late summer average, which is in turn more than half a degree higher than 30 years ago, according to Michael Mannof Penn State University. As a result there was more potential for a deluge.

Are there other links between Harvey and climate change?

Yes, the storm surge was greater because sea levels have risen 20cm as a result of more than 100 years of human-related global warming. This has melted glaciers and thermally expanded the volume of seawater.

