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US 'at risk of mega-drought future' | US 'at risk of mega-drought future' |
(about 7 hours later) | |
The American south-west and central plains could be on course for super-droughts the like of which they have not witnessed in over a 1,000 years. | |
Places like California are already facing very dry conditions, but these are quite gentle compared with some periods in the 12th and 13th Centuries. | Places like California are already facing very dry conditions, but these are quite gentle compared with some periods in the 12th and 13th Centuries. |
Scientists have now compared these earlier droughts with climate simulations for the coming decades. | Scientists have now compared these earlier droughts with climate simulations for the coming decades. |
The study suggests events unprecedented in the last millennium may lie ahead. | The study suggests events unprecedented in the last millennium may lie ahead. |
"These mega-droughts during the 1100s and 1200s persisted for 20, 30, 40, 50 years at a time, and they were droughts that no-one in the history of the United States has ever experienced," said Ben Cook from Nasa's Goddard Institute for Space Studies. | "These mega-droughts during the 1100s and 1200s persisted for 20, 30, 40, 50 years at a time, and they were droughts that no-one in the history of the United States has ever experienced," said Ben Cook from Nasa's Goddard Institute for Space Studies. |
"The droughts that people do know about like the 1930s 'dustbowl' or the 1950s drought or even the ongoing drought in California and the Southwest today - these are all naturally occurring droughts that are expected to last only a few years or perhaps a decade. Imagine instead the current California drought going on for another 20 years." | "The droughts that people do know about like the 1930s 'dustbowl' or the 1950s drought or even the ongoing drought in California and the Southwest today - these are all naturally occurring droughts that are expected to last only a few years or perhaps a decade. Imagine instead the current California drought going on for another 20 years." |
Dr Cook's new study is published in the journal Science Advances, and it has been discussed also at the annual meeting of the American Association for the Advancement of Science. | Dr Cook's new study is published in the journal Science Advances, and it has been discussed also at the annual meeting of the American Association for the Advancement of Science. |
There is already broad agreement that the American Southwest and the Central Plains (a broad swathe of land from North Texas to the Dakotas) will dry as a consequence of increasing greenhouse gases in the atmosphere. But Dr Cook's research has tried to focus specifically on the implications for drought. | There is already broad agreement that the American Southwest and the Central Plains (a broad swathe of land from North Texas to the Dakotas) will dry as a consequence of increasing greenhouse gases in the atmosphere. But Dr Cook's research has tried to focus specifically on the implications for drought. |
His team took reconstructions of past climate conditions based on tree ring data - the rings are wider in wetter years - and compared these with 17 climate models, together with different indices used to describe the amount of moisture held in the soils. | His team took reconstructions of past climate conditions based on tree ring data - the rings are wider in wetter years - and compared these with 17 climate models, together with different indices used to describe the amount of moisture held in the soils. |
The use of the palaeo-information, Dr Cook said, allowed the simulations to capture the full extent of the natural variability that exists in the climate system, giving his team a better feel for what is normal and what is extreme. | The use of the palaeo-information, Dr Cook said, allowed the simulations to capture the full extent of the natural variability that exists in the climate system, giving his team a better feel for what is normal and what is extreme. |
And what the group found was clear and consistent: that after 2050, the Southwest and the Central Plains would likely shift to drier conditions that exceeded even the great drought epochs of the so-called "Medieval Climate Anomaly" in the 12th and 13th Centuries. | And what the group found was clear and consistent: that after 2050, the Southwest and the Central Plains would likely shift to drier conditions that exceeded even the great drought epochs of the so-called "Medieval Climate Anomaly" in the 12th and 13th Centuries. |
The cause of the drying was twofold: reduced precipitation - that is, reductions in rainfall and snowfall; but also increased evaporation, driven by higher temperatures, leading to more parched soils. | The cause of the drying was twofold: reduced precipitation - that is, reductions in rainfall and snowfall; but also increased evaporation, driven by higher temperatures, leading to more parched soils. |
"In both the Southwest and Central Plains, we're talking about levels of risk of 80% of a 35-year-long drought by the end of the century, if climate change goes unmitigated," said co-author Toby Ault from Cornell University. | "In both the Southwest and Central Plains, we're talking about levels of risk of 80% of a 35-year-long drought by the end of the century, if climate change goes unmitigated," said co-author Toby Ault from Cornell University. |
"And that's a really important point - we're not necessarily locked into these high levels of mega-drought risk if we take actions to slow the effects of rising greenhouse gases on global temperatures." | "And that's a really important point - we're not necessarily locked into these high levels of mega-drought risk if we take actions to slow the effects of rising greenhouse gases on global temperatures." |
Asked to define mega-drought conditions more precisely, Dr Ault used the example of Tucson, Arizona, where precipitation has been at 80% of expected levels since the late 1990s. If that continued for another two decades, it would qualify as mega-drought conditions, he said. | Asked to define mega-drought conditions more precisely, Dr Ault used the example of Tucson, Arizona, where precipitation has been at 80% of expected levels since the late 1990s. If that continued for another two decades, it would qualify as mega-drought conditions, he said. |
The Cornell researcher told reporters that modern America would certainly be challenged by such aridity, but that strategies could be found to cope. | The Cornell researcher told reporters that modern America would certainly be challenged by such aridity, but that strategies could be found to cope. |
"The records we have of past mega-droughts are based on tree-ring width estimates, and if you think that through, that's a little bit encouraging because it means the events weren't so bad as to kill off all the trees. I am optimistic that we can cope with the threat of mega-drought in the future because it doesn't mean no water - it just means significantly less water than we're used to having from the 20th Century," Dr Ault explained. | "The records we have of past mega-droughts are based on tree-ring width estimates, and if you think that through, that's a little bit encouraging because it means the events weren't so bad as to kill off all the trees. I am optimistic that we can cope with the threat of mega-drought in the future because it doesn't mean no water - it just means significantly less water than we're used to having from the 20th Century," Dr Ault explained. |
Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos | Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos |
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