Wednesday, April 20, 2016

Climate disruption and extreme weather

From Facebook post by Katharine Hayhoe
Apr. 19, 2016

Houston and southeast Texas is being hammered by devastating rain and flood this week--flooding homes, damaging infrastructure, and even leading to loss of life. In this age of digital media we often become inured to pictures of disaster; but when it's happening somewhere you're familiar with, affecting people you know, it is very real.

When disaster like this strikes, the most common question for climate scientists is, "is this natural? or is it climate change?" But this is like asking our cardiologist, after a frightening and unexpected heart attack, "is this genetic? or is it my lifestyle?"


As a cardiologist would say, however, often our lifestyle choices - what we eat, and how much we do (or don't) exercise - exacerbate our health risks. In the same way, our collective lifestyle choices as the human race - depending on fossil fuels for most of our energy, as we have over the past three centuries - exacerbate our risks of heavy precipitation.

The physics connecting a warming world to heavier precipitation has been well established since the 1800s. As the planet warms, more water evaporates from oceans, lakes, rivers and streams. When the "genetic risk" of a naturally-occurring storm comes along, as it usually does at this time of year, there is now on average more "lifestyle-enhanced" water vapour available for it to pick up and dump on us than there would have been 50 or 100 years ago.

This year, though, the situation is particularly dire. Over the last few decades, we've seen record-breaking years and months. But these typically occur one at a time, broken up by more "normal" conditions. Global temperature records aren't usually smashed in long continuous strings; yet that's exactly what we've seen recently. 2014 was the warmest year on record, quickly surpassed by 2015; every month in 2016 has been remarkably warmer than average, so far; and NASA Goddard's Gavin Schmidt, one of the smartest and most knowledgeable climate scientists I know, estimates a >99% chance of 2016 breaking records as well.

What does this astonishing string of record-breaking temperatures mean for extreme precipitation risks? Simply this: the warmer the planet, the greater the amount of extra water available for storms to sweep up and dump on us. And the terrible events this week illustrate how - nine times out of ten - climate change doesn't bring strange and new impacts we've never seen before; it takes the naturally-occurring risks we've already faced in the past, and gives them steroids.

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