Tree Rings And Weather Data Warn Of Megadrought

| Educate!

Above photo: A drought in 2011 parched O. C. Fisher Lake in San Angelo, TX. Tony Gutierrez/AP.

Farmers in the US West know they have a drought, but may not yet realise these arid years could become a megadrought.

London -Climate change could be pushing the US west and northern Mexico towards the most severe and most extended period of droughtobserved in a thousand years of US history, a full-blown megadrought.

Natural atmospheric forces have always triggered prolonged spells with little rain. But warming driven by profligate human use of fossil fuels could now be making a bad situation much worse.

The warning of what climate scientists call a megadrought – outlined in the journal Science – is based not on computer simulations but on direct testimony from more than a century of weather records and the much longer story told by 1200 consecutive years of evidence preserved in the annual growth rings of trees that provide a record of changing levels of soil moisture.

“Earlier studies were largely model projections of the future. We are no longer looking at projections, but at where we are now,” said Park Williams, a bioclimatologist at the Lamont Doherty Earth Observatory of Columbia University in the US.

“We now have enough observations of current drought and tree ring records of past drought to say we’re on the same trajectory as the worst prehistoric droughts.”

Repeating the past

Previous research has already linked catastrophic drought to turmoil among pre-Columbian civilisations in the American Southwest.

Studies by other groups have also warned that what happened in the past could happen again, as carbon dioxide emissions from fossil fuel combustion enrich the atmosphere, raise temperatures and parch the soils of the US West.

Global heating has been repeatedly linked to the last devastating drought in California, and to the possible return of Dust Bowl conditions in the Midwestern grain belt.

The latest study delivers a long-term analysis of conditions across nine US states, from Oregon and Montana in the north down to California, New Mexico and part of northern Mexico.

With the evidence preserved in old tree trunks, the scientists identified dozens of droughts in the region from 800 AD. They found four megadroughts – periods in which the conditions became extreme – between 800 and 1600. Since then there have been no droughts that could be matched with these – so far.

And then the researchers matched the megadrought tree ring evidence with soil moisture records collected in the first 19 years of this century, and compared this with any 19-year period in the prehistoric droughts.

“We’ll need more and more good luck to break out of drought, and less and less bad luck to get into drought”

They found that the current prolonged dry spell is already more pronounced than the three earliest records of megadrought. The fourth megadrought – it ran from 1575 to 1603 – may still have been the worst of all, but the match with the present years is so close that nobody can be sure.

But the team behind the Science study is sure of one thing. This drought right now is affecting wider stretches of landscape more consistently than any of the earlier megadroughts, and this, they say, is a signature of global heating. All the ancient megadroughts lasted longer, and sometimes much longer, than 19 years, but all began in a way very similar to the present.

The snowpack in the western high mountains has fallen dramatically, the flow of the rivers has dwindled, lake levels have fallen, farmers have been hit and the wildfires have become more prolonged and more intense.

Drought and even the chance of megadrought may be a fact of life in the US West. During occasional natural atmospheric cycles, the tropical Pacific cools and storm tracks shift further north, taking rainfall away from the US drylands.

But since 2000, average air temperatures in the western states have risen by more than 1.2°C above the normal over earlier centuries. So soils already starved of rain began to lose their stored moisture at an ever-increasing rate.

Worsened by heating

Without the additional global heating, this drought might have happened anyway, and perhaps even been the 11th worst ever recorded, rather than almost the worst ever in human experience.

“It doesn’t matter if this is exactly the worst drought ever,” said Benjamin Cook, a co-author, from Nasa’s Goddard Institute for Space Studies. “What matters is that it has been made much worse than it could have been because of climate change.”

The researchers also found that the 20th century was the wettest century in the entire 1200 year record, and this relatively plentiful supply of water must have helped enrich the US West and make California, for instance, become the Golden State, the most populous in the US.

“Because the background is getting warmer, the dice are increasingly loaded towards longer and more severe droughts,” Professor Williams said. “We may get lucky, and natural variability will bring more precipitation for a while.

“But going forward, we’ll need more and more good luck to break out of drought, and less and less bad luck to get into drought.” – Climate News Network

  • voza0db

    The researchers also found that the 20th century was the wettest century in the entire 1200 year record“… SO, we are just returning to normal!

  • didactic1

    Exacerbate droughts? Human heat sources logically do. But no proof here the extended drought would not have occurred otherwise. How did a superdrought occur in 16 cent? No industry, no fossil fuels, relatively no people. Nature can be ruthless.

  • didactic1

    Did conquistadors in 16 cent have tanks, coal and endless BBQ?

  • voza0db

    Yep… Back then our technology was WAY SUPERIOR.

  • didactic1

    Great horses, quality crafts. And organic food!


  • larrysherk

    We are going through a time of lessons, with a pandemic, a drought where we grow food, a solar minimum offering unusual frosts, and an apparently ruined debt-ridden economy. And in foreign policy, the United States is clearly on the wrong side of history. Instead of using the UN for cooperation, we have weaponized it, where protecting our “interests” is almost invariably at the expense of someone else, someone less powerful. It is a shame that it has come to this, but we will pay even worse unless we start recognizing Gaia and stewardship.

  • larrysherk

    The evidence of global warming has been fairly decent, but the evidence that it is anthropogenic is very sketchy and unreliable. Nature would not be ruthless if we weren’t so acquisitive and greedy. The planet was put here for our care-taking, not for our plundering.

  • didactic1

    Planet was spun off by gravity from other mass as part of a process no one completely under stand. Most matter is dark matter.

  • Aaron Aarons

    The planet was not “put here”. Such superstitious nonsense interferes with our collective ability to actually understand the world we inhabit.

  • larrysherk

    Sorry you don’t believe in stewardship and our sacred relation to Gaia. That is not superstitious nonsense but demonstrated indigenous wisdom. You don’t have to believe that way, but be aware that thousands upon thousands do. This is actually a huge asset to scientific understanding, as many scientists like Gregg Braden have found. Calling things you don’t grasp “nonsense” just gets in your own way.

  • jwreitter

    After studying this I think massive, prolonged drought is worse than wildfires, storms, searise, heatwaves and floods. They are all related but megadroughts will have the greatest impact on thirst and starvation. Water tables and ancient aquifers are rapidly being depleted. Topsoil is being blown away or washed away. Arable land is shrinking and deserts are expanding faster than ever.

    This is not a problem that can be resolved by digging deeper wells because we have just about hit rock bottom in most countries. Melting glaciers and mountain snowfall have provided some relief, but that is only temporary. Desalinization is too limited and too expensive for the masses. Suffering and death will be the fate of humanity unless drastic action is taken to reduce GHGs, greenhouse gasses, that are heating our planet and desiccating our forests, gardens and farmlands.

    Water will soon be the new gold. Wars will be fought for agua, and are already happening. And already millions are dying of thirst every year. Soon only polluted water and salt water will be available for over a billion people.

  • Nylene13

    We don’t know that. Advanced Aliens could be creating planets all over the universe, for all we know.

    Regardless, we were better off when the Earth and Mother Nature were regarded as Sacred, not toilets for Capitalism, as is presently the case.

  • Jon

    Purge the massive oil pipelines and bring water from the Great Lakes.

  • Jon

    SOMETHING caused the earlier droughts. This time it may well be human caused. No contradiction.

  • larrysherk

    My beliefs don’t interfere with anything. We have room for a variety of spiritual and religious persuasions. From my science training, (PhD chemical physics 1968), I would suggest that “actually understanding” our world is quite beyond science, and is part of the great discovery forty years ago of the colossal overlap between natural science and spirituality (Gregg Braden)