Climate Change

Warming planet may drive return of ‘medieval megadroughts’ in US

Rapid increase in aridity and sea surface temperatures around the globe because of human-activities may lead to severe droughts

 
By DTE Staff
Last Updated: Thursday 25 July 2019
Photo: Getty Images

Human-induced rise in global average surface temperatures could trigger megadroughts — severe droughts that last for decades — in the United States that were much prevalent during medieval times, according to a study.

Megadroughts were a notable feature during the 9th through the 15th centuries in the American Southwest, according to the study, published in the journal Science Advances.

While the medieval megadroughts were a result of natural climate variability, rapid increase in aridity and sea surface temperatures around the globe because of human-activities could spark their return, said a team of scientists at Columbia University’s Lamont-Doherty Earth Observatory.

To understand what triggers these megadroughts, the team reconstructed aquatic climate data and sea-surface temperatures from the last 2,000 years. They found three key reasons:

  • Radiative forcing — when Earth absorbs more sunlight than it radiates back into space — and a decrease in volcanic activity
  • Severe and frequent La Niña events — cool tropical Pacific sea surface temperatures that cause changes to global weather events
  • Warm conditions in the Atlantic

High radiative forcing increases heat, which then lead to greater evaporation. Simultaneously, a warmer than usual Atlantic sea-surface temperatures combined with very strong and frequent La Niñas decreases precipitation in the already dried-out area.

Of these, repeated La Niña conditions were behind the megadroughts in the American southwest, the study showed.

“Because you increase the baseline aridity, in the future when you have a big La Niña, or several of them in a row, it could lead to megadroughts in the American West,” explained lead author Nathan Steiger, a Lamont-Doherty Earth Observatory hydroclimatologist, in a release.

The US Southwest and Great Plains are likely to experience persistent drought during the second half of the 21st century, according to a previous study.

It will be worse than anything seen in times ancient or modern, with the drying conditions “driven primarily” by human-induced global warming, it added.

The rate at which the climate is warming, currently, is 'unparalleled' in the past 2,000 years, the BBC reported, citing an research published in the Nature.

The medieval warm period (between AD 950 and AD 1250) saw significant rise in temperature across 40 per cent of the Earth's surface. On the other hand, the current warming impacts the vast majority of the world, the report said.

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