Tuesday, August 29, 2017

It's a Fact, Jack/Jill

Climate Change

There is both ink and words on whether Tropical Storm Hurricane Harvey was "caused by" climate change.

What can be said is nicely summarized by climate scientist Michael Mann, writing for the The Guardian who steers us away from the notion of causation (this is, as he says an "ill-posed question") to evidence about worsening and exacerbating the flooding that followed.

His short article is worth reading. These are some of  the factors at play which he describes in more detail

--A combination of sea level rise and coastal subsidence due to human disturbance led to a higher storm surge.

--Regional ocean surface temperatures have risen almost 1 degree Fahrenheit (about 0.5 degrees Centigrade over time. Mann notes that there is rough relationship between average atmospheric moisture content and each increase of 0.5 degrees Centigrade of warming. The result is some 3-5% increase in moisture in the atmosphere.

--Not only is the surface of the ocean warmer than it used to be, the warming effect of global climate change is penetrating into deeper layers. This means that the surface layer can "feed" on warmer water below.

--Many reports have emphasized that Harvey stalled, stayed in place moving only slowly away from where it made landfall. The prevailing winds are weak so the storm spun and wobbled almost in place. Mann writes that this pattern "is associated with a greatly expanded subtropical high pressure system over much of the US at the moment, with the jet stream pushed well to the north. This pattern of subtropical expansion is predicted in model simulations of human-caused climate change."
 The take home message: global climate change worsened this ferocious storm. It is also important to note that this is based on evidence.
And this is the fact to which I refer.

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