Climate change obliterated Greenland's leafy cover, turning it into an
icy island, a new study says
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Extensive spruce forests used to cover the southern half of Greenland,
according to a Canadian study that gives a remarkable glimpse of the
icy island's green past and possible future.

The work, by a team at the Universite du Quebec a Montreal, shows the
impact of past climate warming on the massive ice sheet was much
greater than previously believed.

And it "should increase concerns about its fate" as the global climate
warms because of increasing greenhouse gas emissions, Anne de Vernal
and Claude Hillaire-Marcel report in the journal Science Friday.

The journal also features a second report showing how North America's
climate suddenly flipped from a cold to a warm state at the end of the
last ice age, with dramatic changes in atmospheric circulation in as
little as a single year.

The shifts happened so quickly it is "as if someone had pushed a
button," says Dorthe Dahl-Jensen of the University of Copenhagen, who
led the international team that found the distinct signature of the
sudden changes in a Greenland ice core. There were two huge
temperature spikes in the Northern Hemisphere at the end of last ice
age - one 14,700 years ago associated with a 10-degree Celsius rise in
temperatures over 50 years. Then icy conditions returned before
another abrupt warming about 11,700 years ago.

The ice core points to a "reorganization" of atmospheric circulation
over one or two years in the Northern Hemisphere before each
temperature spike, say the scientists. The findings are based on dust,
oxygen and hydrogen found in the annual layers of ice that have
collected in Greenland over the eons.

The abrupt transitions they see occurred at the end of the last ice
age as the planet warmed up from extremely cold conditions. It is not
clear if such sudden changes could occur in today's relatively warm
climate.

But the scientists say there is a "pressing" need to find out if such
abrupt change could be triggered by the greenhouse gases being pumped
into the atmosphere today.

The Canadian report fills in a significant gap in Greenland's history
and how its ice has waxed and waned over time.

It is based on pollen found in sediments taken near Cape Farewell at
the southern tip of Greenland. The sediment cores, dating back almost
a million years, were collected by the international ocean drilling
program and analyzed in De Vernal's lab.

The pollen shows Greenland was much greener than it is today during
several warm periods over the million-year span, with extensive
fernlike vegetation 125,000 ago and widespread spruce forests 400,000
years ago.

"It was probably much like the forest in Norway is today, with a
relatively mild climate," de Vernal said in a telephone interview from
France, where she is travelling this week.

Knowing how much the Greenland ice sheet shrank in the past is key to
better understanding vulnerability of the ice sheet today, said
University of Alberta paleoclimatologist Alexander Wolfe, co-author of
a Science commentary that discusses the findings.

If all of Greenland's ice were to melt it would raise the global sea
level close to seven metres - "that's enough to submerge all of
Bangladesh, the Pacific Islands and much of Florida," says Wolfe.

The new study is reassuring in that it shows it took a prolonged
20,000-year warm period to melt back the ice sheet enough to allow
spruce forests to grow over the southern half of Greenland.

But Wolfe notes that humans have now added a wild card into the equation.

"What's remarkable about this (the past ice retreats) is that they
occurred with greenhouse gas emissions that are about 30 per cent
lower than they are today," he says.