The heat wave and human influence on climate

Most of the United States just endured a remarkable heat wave in which hundreds of daily temperature records were broken and a number of all-time high records were also broken.  Additionally, because of the flooding of the Mississippi River, humidity levels were also very high, leading to extremely high heat indexes, as high as 131 degrees in Knoxville, Iowa on Monday, July 18.

The standard line regarding extreme weather events has generally been, "It is almost impossible to attribute a particular weather event to climate change, so--no--this heat wave was not caused by climate change."  I think that statement has become more and more inaccurate as the amount of CO2 in the atmosphere continues to rise.

I think the new statement should be, "Because humans have changed the chemistry of the atmosphere, all weather now has the fingerprint of human-caused climate change on it.  So, yes, this extreme weather was affected by climate change."

The exact differences between this heat wave and the hypothetical heat wave that would have occurred in a world with a CO2 concentration of 290 ppm is impossible to know.  But what we do know is that it was different.  It almost certainly was hotter and more humid that it otherwise would have been.  So, no, this heat wave was not "caused" by climate change.  But it most certainly was exacerbated by it.

Enjoy the new world we now inhabit!

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