Washington: Scientists have claimed
that global wind shifts many have ushered in a warmer climate
and the birth of human civilisation at the end of the last Ice
Age about 20,000 years ago.
An international team has looked to a global shift
in winds and propose a chain of events that began with melting
of the large northern hemisphere ice sheets about 20,000 years
ago, the 'Science' journal reported.
The melting ice sheets reconfigured the planet's wind
belts, pushing warm air and seawater south, and pulling carbon
dioxide from the deep ocean into the atmosphere, allowing the
planet to heat even further. Their hypothesis makes use of
climate data preserved in cave formations, polar ice cores and
deep-sea sediments to describe how Earth finally thawed out.
"Finally, we have a clear picture of the global
teleconnections in Earth's climate system that are active
across many time scales.
"These same linkages that brought the earth out of the
last ice age are active today, and they will almost certainly
play a role in future climate change as well," Bob Anderson at
Columbia University, who led the team.
Earth regularly goes into an ice age every 100,000
years or so, as its orientation toward the sun shifts in what
are called Milankovitch cycles.
At the peak of the last ice age, about 20,000 years
ago, with New York City and large parts of Europe and Asia
buried under thick sheets of ice, Earth's orbit shifted.
It may sound counterintuitive, but the scientists say
freshening of the North Atlantic triggered a series of cold
spells in Greenland and northern Europe by shutting down the
Gulf Stream current, which usually carries warm water north
from the equator.
By 16,000 years ago, the glaciers had beaten a
spectacular retreat. This shift in westerly winds would also
amplify the warming in both hemispheres by resetting the
planet's thermostat, according to the scientists.
The displaced westerlies caused heavy mixing in the
Southern Ocean around Antarctica, pumping dissolved carbon
dioxide from the water into the air. Ice core records show
that between 18,000 and 11,000 years ago atmospheric carbon
dioxide levels rose from 185 parts per million to 265 parts
First Published: Saturday, June 26, 2010, 13:10