Earth Could Plunge Into Sudden Ice
In the film, "The Day After Tomorrow," the world gets
gripped in ice within the span of just a few weeks. Now research
now suggests an eerily similar event might indeed have occurred
in the past.
Looking ahead to the future, there is no reason why such a freeze
shouldn't happen again and in ironic fashion it could be
precipitated if ongoing changes in climate force the Greenland
ice sheet to suddenly melt, scientists say.
Starting roughly 12,800 years ago, the Northern Hemisphere was
gripped by a chill that lasted some 1,300 years. Known by scientists
as the Younger Dryas and nicknamed the"Big Freeze,"
geological evidence suggests it was brought on when a vast pulse
of fresh water a greater volume than all of North America's
Great Lakes combined poured into the Atlantic and Arctic
This abrupt influx, caused when the glacial Lake Agassiz in North
America burst its banks, diluted the circulation of warmer water
in the North Atlantic, bringing this "conveyer belt"
to a halt. Without this warming influence, evidence shows that
temperatures across the Northern Hemisphere plummeted.
No time to react
Previous evidence from Greenland ice samples had suggested this
abrupt shift in climate happened over the span of a decade or
so. Now researchers say it surprisingly may have taken place over
the course of a few months, or a year or two at most.
"That the climate system can turn on and off that quickly
is extremely important," said earth system scientist Henry
Mullins at Syracuse University, who did not take part in this
research. "Once the tipping point is reached, there would
be essentially no opportunity for humans to react."
For two years, isotope biogeochemist William Patterson at the
University of Saskatchewan in Canada and his colleagues investigated
a mud core a tube of mud taken from the ancient
lake Lough Monreach in Ireland. Because this sediment was deposited
slowly over time, each layer from this core effectively represents
a snapshot of history, with slices just a half-millimeter thick
presenting one to three months.
"Basically, I drive around in western Ireland looking for
the right conditions bedrock, vegetation and lake
to obtain the most complete record of climate," Patterson
By looking at isotopes of carbon in each slice, the researchers
could deduce how productive the lake was. When plants grow in
lakes, they prefer carbon-12 to make up their organic tissue
that is, carbon atoms that have 12 protons and neutrons in total
in their nucleus. This leaves the lake water with relatively more
carbon-13. At the same time, oxygen isotopes give a picture of
temperature when animals or plants produce calcium carbonate,
the ratio of oxygen-16 and oxygen-18 isotopes within are related
At the start of the Younger Dryas, Patterson and his colleagues
discovered temperatures and lake productivity dropped over the
course of just a few years.
"It would be like taking Ireland today and moving it up
to above the Arctic Circle, creating icy conditions in a very
short period of time," Patterson said.
Their findings also suggest that it may have taken 100 to 200
years before the lake and climate recovered, rather than the decade
or so that Greenland ice cores had indicated.
"This makes sense because it would take time for the ocean
and atmospheric circulation to turn on again," Patterson
The discrepancies between the evidence from the mud core and
the ice cores might be due to disturbances in how material flowed
within the ice. "Sometimes there's melting, and you have
percolation of material between layers, which can blur the records,"
Patterson explained. "We found a core that had not been disturbed
even on a millimeter by millimeter basis, so the sediment had
been layered in order since it was deposited."
Looking ahead to the future, Patterson said there was no reason
why a big freeze shouldn't happen again.
Reference Sources 135
December 3, 2009