Human behavior did not cause this climate change. Instead, climate warming caused behavioral change (10 million mouths to feed became 30 million).

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WASHINGTON

We know, because they often say so, that those who think catastrophic global warming is probable and perhaps imminent are exemplary empiricists. They say those who disagree with them are "climate change deniers" disrespectful of science.

Actually, however, something about which everyone can agree is that of course the climate is changing it always is. And if climate Cassandras are as conscientious as they claim to be about weighing evidence, how do they accommodate historical evidence of enormously consequential episodes of climate change not produced by human activity? Before wagering vast wealth and curtailments of liberty on correcting the climate, two recent books should be considered.

In "The Third Horseman: Climate Change and the Great Famine of the 14th Century," William Rosen explains how Europe's "most widespread and destructive famine" was the result of "an almost incomprehensibly complicated mixture of climate, commerce, and conflict, four centuries in gestation." Early in that century, 10 percent of the population from the Atlantic to the Urals died, partly because of the effect of climate change on "the incredible amalgam of molecules that comprises a few inches of soil that produces the world's food."

In the Medieval Warm Period (MWP), from the end of the ninth century to the beginning of the 14th, the Northern Hemisphere was warmer than at any time in the last 8,000 years for reasons concerning which there is no consensus. Warming increased the amount of arable land there were vineyards in northern England leading, Rosen says, to Europe's "first sustained population increase since the fall of the Roman Empire." The need for land on which to grow cereals drove deforestation. The MWP population explosion gave rise to towns, textile manufacturing and new wealthy classes.

Then, near the end of the MWP, came the severe winters of 1309-1312, when polar bears could walk from Greenland to Iceland on pack ice. In 1315 there was rain for perhaps 155 consecutive days, washing away topsoil. Upwards of half the arable land in much of Europe was gone; cannibalism arrived as parents ate children. Corpses hanging from gallows were devoured.

Human behavior did not cause this climate change. Instead, climate warming caused behavioral change (10 million mouths to feed became 30 million). Then climate cooling caused social changes (rebelliousness and bellicosity) that amplified the consequences of climate, a pattern repeated four centuries later.

Go here to read the rest:
George F. Will: History shows how human behavior changes along with climate