http://ecowatch.com/2015/02/13/nasa-megadroughts-human-induced-climate-change/
[video, image and links in on-line article]
NASA Scientists: Future Megadroughts Could Last 30+ Years ‘Thanks to
Human-Induced Climate Change’
Anastasia Pantsios | February 13, 2015 2:08 pm
The drought in California, going into its fourth year, has been in the
news, especially since California produces much of the country’s food.
But a new NASA study, published this week in the journal Science
Advances, suggests that the U.S. could be looking at much worse. It
predicts multi-decade “megadroughts” of more than 30 years by the end of
the 21st century if we don’t significantly reduce greenhouse gas emissions.
“Recent droughts such as the ongoing drought in California or the
Southwest, or even historical droughts such as the Dust Bowl in the
1930s, these are naturally occurring droughts that typically last
several years or sometimes almost a decade,” said the study’s lead
author Ben Cook, a climate scientist at NASA’s Goddard Institute for
Space Studies and Columbia University’s Lamont-Doherty Earth
Observatory. “What we’re seeing is that with climate change many of
these types of droughts will likely last for 20, 30, sometimes even 40
years.”
How bad these droughts will get is tied to how much greenhouse gas
emissions humans generate in future years. Cook and his colleagues say
the current risk of a megadrought is 12 percent. If greenhouse gas
emissions stop increasing by the mid-21st century, they project the risk
at more than 60 percent in the second half of the 21st century. And if
they continue to rise at current rates, the researchers say, there is an
80 percent chance of a megadrought in the Southwest and Central Plains
between 2050 and 2099. “Alternatively, if the world were to take
aggressive actions to reduce emissions, the model still showed drought
but the trends would be less severe,” they found.
Cook said this study is more robust than previous research, which used
fewer drought indictors and few climate models. This study used 17
different climate models, all of which showed a drier planet “thanks to
human-induced climate change,” says NASA.
“What I think really stands out in the paper is the consistency between
different metrics of soil moisture and the findings across all the
different climate models,” said climate scientist Kevin Anchukaitis of
Woods Hole Oceanographic Institution, who was not involved in the study.
“It is rare to see all signs pointing so unwaveringly toward the same
result, in this case a highly elevated risk of future megadroughts in
the United States.”
This is also the first study to compare future drought projections to
droughts over the last 1,000 years, using tree-ring information to
estimate droughts beyond the last 150 years. The researchers looked at
megadroughts of 30-50 years that occurred in North America between 1100
and 1300 and compared them with projected late 21st-century droughts.
They found that whether greenhouse gas emissions stop increasing or
continue to increase at the current rate, the likelihood of drier
conditions and droughts lasting 30 years or more is greater.
“We can’t really understand the full variability and the full dynamics
of drought over western North America by focusing only on the last
century or so,” said Cook. “We have to go to the paleoclimate record,
looking at these much longer timescales, when much more extreme and
extensive drought events happened, to really come up with an
appreciation for the full potential drought dynamics in the system.”
Anchukaitis agreed that comparing medieval-era droughts with projected
ones is useful.
“Those droughts had profound ramifications for societies living in North
America at the time,” he said. “These findings require us to think about
how we would adapt if even more severe droughts lasting over a decade
were to occur in our future.”
Those adaptations would be more challenging than anything we’ve seen in
the past, says Cook.
“The droughts represent events that nobody in the history of the U.S.
has ever had to deal with,” he said. “Even in the modern era, droughts
such as the ongoing droughts in California and the Southwest, these
normal droughts act as major stressors on water resources in the region.
So we expect that with these much longer droughts, it’s going to be even
more impactful and cause even more problems for agriculture and
ecosystems in the region.”
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