July 11, 2017, by Tim Radford
LONDON, 11 July, 2017
– Here is the long-term
weather forecast for the heart of the Middle East. There
will be 10,000 years of drought before rainfall increases significantly. If
anything, rainfall will decrease.
And then, 100 centuries from
now, subtle shifts in the planetary orbit and Earth’s axis will combine to
bring a climate shift. Slightly more sunlight will fall on Eurasia, the climate
regime of the North Atlantic will shift and the Mediterranean storms will
return, bringing with them more rain.
The hard evidence for this
story of future climate is locked in subterranean stalagmites, calcium
carbonate deposits that grow slowly upwards on the floor of a cave in northern
Iran.
A team of Iranian and US-based
scientists used a sophisticated measuring technique – the shorthand for it is
uranium-thorium geochronometry – to date their stalagmite samples and then use
them to “read” the climate history of the region.
They report in the
journal Quaternary Science Reviews that their samples and the isotope
evidence within them spanned a record of annual rainfall – and therefore
regional weather – for a period that began 127,000 years ago and ended 73,000
years ago, and another that spanned 7,500 to 6,500 years ago.
No relief foreseeable
And the evidence says: the
drought is not going to end any time soon, whatever the politicians might say.
“Local governments generally
prefer the narrative that the region is only in a temporary dry spell and
better prospects of water availability lie ahead,” said Sevag Mehterian, based at
the University of Miami Rosenstiel School, who led the research.
“Our study has found evidence
to the contrary, suggesting that, in fact, the future long-term trend based on
paleoclimate reconstructions is likely towards diminishing precipitation, with
no relief in the form of increased Mediterranean storms, the primary source of
annual precipitation to the region, in the foreseeable future.”
The Eastern Mediterranean is
right now in the
grip of the worst drought for the last 900 years. The collapse of
agriculture, as the fields parch and the wells begin to dry up, has been linked to
the catastrophic conflict in Syria.
Researchers have attributed a
calamitous dust storm that in 2015 obscured seven Middle East nations from
satellite view to human-induced climate change, but recent
evidence from the Dead Sea region has delivered a reminder that the region
has always been vulnerable to devastating drought.
All such forecasts need to be
placed in context: this one is so far consistent with evidence from other
caves, but like all use of what climate scientists call “proxy evidence” – a
category that includes fossilised pollen in lake beds, tree growth ring counts,
ice cores from ancient glaciers and so on – it could be subverted or overturned
by some future discovery.
The prediction does not take
into account any of the future global shifts that could follow climate change
driven by ever-rising ratios of greenhouse gases in the atmosphere as a
consequence of fossil fuel consumption: this is the human dimension.
And, of course, humans in the
region have already
seen whole civilisations collapse because of drought in the last few
thousand years, and have quite enough to worry about as regional temperatures
rise over the next century or so to, in some locations, potentially
lethal levels.
But the Iranian evidence
points to enduring harsh conditions in the very long term. The challenge is for
other scientists to confirm or to challenge their conclusions, and for
politicians to find ways to prepare for a thirstier tomorrow.
“We take what we have learned
from the past climate and applied it to better understand what to expect moving
forward with the current state of the changing global climate,” said Ali
Pourmand, a marine geoscientist at the University of Miami, and one of
the authors.
– Climate News Network
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