Recent Extreme Heatwaves Were Caused by Climate Change - Even Moderate Heat Has Doubled

New research published today in Proceedings of the National Academy of Sciences concludes that extreme heatwaves have have increased 50 times over the past 30 years and that climate change is to blame.

James Hansen writes in the Washington Post (my emphasis),

This is not a climate model or a prediction, but actual observations or weather events and temperatures that have happened. Our analysis shows that it is no longer enough to say global warming will increase the likelihood of extreme weather and to repeat the caveat that no individual weather even can be directly linked to climate change. To the contrary, our analysis shows that, for the extreme hot weather of the recent past, there is virtually no explanation other than climate change.

The European heatwave of 2003, the Russian heatwave of 2010, and the record-breaking drought in Texas last year... All climate change. The ongoing drought across over half the US, and record-breaking heat this year? The data isn't fully in yet, but Hansen says it's likely the conclusion will be the same. All of it, climate change.

No doubt the word 'virtually' will be seized upon as a sliver of an opening to attempt to break apart Hansen's statement.

Mongabay sums up the statistical basis for Hansen's confidence:

Between 1981 and 2010, extreme heatwaves covered 10 percent of the world, according to the paper, which is 50 to 100 times greater than the 0.1 percent to 0.2 percent of the Earth's surface covered by extreme heat from 1951-1980. The analysis not only finds that extreme heatwaves (defined as over three standard deviations above the base period) have expanded due to a warming world, but that moderate heat (over half of a standard deviation) has more than doubled: jumping from 33 percent to 75 percent. Many climatologists refer to this phenomenon as "loading the climate dice."

Continuing the loaded dice analogy, Hansen says that rather than two-sides of a die representing warmer than normal weather, we're now in a situation where four sides of the die represent warmer than normal weather, with one of those faces being extreme heat.

Perhaps its still too soon, but what I want to know is how long should it be before we start just accepting that what we now call an extreme heat wave, based on weather observations over the past century or so, is just a new normal heat wave. In terms of weather at least, the world is a fundamentally different place now from when weather observations started in the US in the late 1800s.

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