Guest essay by Eric Worrall

According to New Scientist, anthropogenic CO2 is making the current drought harsher. But they admit an even worse drought occurred in the 16th century.

US megadrought is being made more intense by effects of climate change

ENVIRONMENT 16 April 2020
By  Adam Vaughan

Climate change caused by humans transformed an otherwise moderate drought in the US and Mexico into one of the driest periods in more than a millennium.

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While the area was known to have suffered past extreme droughts due to natural cycles such as the La Niña climate phenomenon, A. Park Williams at Columbia University, New York, and his colleagues, have now revealed that potentially almost half of the current episode’s severity was down to human-caused global warming. The event was second in intensity only to a megadrought at the end of the 16th century.

Williams’s team worked out the region’s soil moisture, a measure of drought, for the past 1200 years. Calculating figures for the past century was straightforward, using temperature, rainfall and other weather records to construct soil moisture. To go further back in time, they used data from more than 1500 tree-ring records. These give an indication of how rapidly trees grew in a given year, which is based in part on how much water there was in the soil at the time.

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“Even without climate change, we still would have had a drought,” says Williams. “But this drought would have been no big deal without climate change.”

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Read more: https://www.newscientist.com/article/2240738-us-megadrought-is-being-made-more-intense-by-effects-of-climate-change/

The abstract of the study;

Large contribution from anthropogenic warming to an emerging North American megadrought

A. Park Williams¹,*, Edward R. Cook¹, Jason E. Smerdon¹, Benjamin I. Cook¹,², John T. Abatzoglou³,⁴, Kasey Bolles¹, Seung H. Baek¹,⁵, Andrew M. Badger⁶,⁷,⁸, Ben Livneh⁶,⁹

See all authors and affiliationsScience  17 Apr 2020:
Vol. 368, Issue 6488, pp. 314-318
DOI: 10.1126/science.aaz9600

Severe and persistent 21st-century drought in southwestern North America (SWNA) motivates comparisons to medieval megadroughts and questions about the role of anthropogenic climate change. We use hydrological modeling and new 1200-year tree-ring reconstructions of summer soil moisture to demonstrate that the 2000–2018 SWNA drought was the second driest 19-year period since 800 CE, exceeded only by a late-1500s megadrought. The megadrought-like trajectory of 2000–2018 soil moisture was driven by natural variability superimposed on drying due to anthropogenic warming. Anthropogenic trends in temperature, relative humidity, and precipitation estimated from 31 climate models account for 47% (model interquartiles of 35 to 105%) of the 2000–2018 drought severity, pushing an otherwise moderate drought onto a trajectory comparable to the worst SWNA megadroughts since 800 CE.

Read more (paywalled): https://science.sciencemag.org/content/368/6488/314

Unfortunately the full study is paywalled. But as the study authors admit, a worse drought occurred in the late 1500s.

Acting on climate change by eliminating CO2 emissions won’t stop severe droughts from occurring. There weren’t many SUV’s being driven around in the 1500s. But eliminating CO2 would throw away affordable energy, which is our best tool for addressing droughts when they occur.

Affordable energy makes it possible to survive a drought and prosper, by making large scale pumping economically viable. If groundwater runs out, there are regions of the USA with water to spare, which are currently experiencing an abundance of water.

If the situation deteriorates, if the entire USA starts to experience severe drought, affordable fossil fuel energy could be used to power monster desalination plants to make up the shortfall.