Current Melting Of Greenland's Ice
Mimicks 1920s-1940s Event
ScienceDaily (Dec. 13, 2007) — Two researchers
here spent months scouring through old expedition logs and reports, and reviewing
70-year-old maps and photos before making a surprising discovery: They found that the
effects of the current warming and melting of Greenland's glaciers that has alarmed the
world's climate scientists occurred in the decades following an abrupt warming in the
1920s.
Their evidence reinforces the belief that glaciers and
other bodies of ice are exquisitely hyper-sensitive to climate change and bolsters the
concern that rising temperatures will speed the demise of that island's ice fields,
hastening sea level rise.
The work, recently reported at the annual meeting of the American Geophysical Union in San
Francisco , may help to discount critics' notion that the melting of Greenland 's glaciers
is merely an isolated, regional event.
They recently recognized from using weather station records from the past century that
temperatures in Greenland had warmed in the 1920s at rates equivalent to the recent past.
But they hadn't confirmed that the island's glaciers responded to that earlier warming,
until now.
“What's novel about this is that we found a wealth of information from low-tech
sources that has been overlooked by most researchers,” explained Jason Box, an
associate professor of geography at Ohio State University and a researcher with the Byrd
Polar Research Center. Many researchers, he says, rely heavily on information from
satellites and other modern sources.
Undergraduate student Adam Herrington, co-author on this paper and a student in the School
of Earth Sciences, spent weeks in the university's libraries and archives, scouring the
faded, dusty books that contained the logs of early scientific expeditions, looking
primarily for photos and maps of several of Greenland 's key glaciers.
“I must have paged through more than a hundred such volumes to get the data we needed
for this study,” Herrington said.
They concentrated on three large glaciers flowing out from the central ice sheet towards
the ocean – the Jakobshavn Isbrae, the Kangerdlugssuaq and the Helheim.
“These three glaciers are huge and collectively, they drain as much as 40 percent of
the southern half of the ice sheet. All three have recently increased their speed as the
temperature rose,” Box said, adding that the Kangerdlugssuaq, at 3.1 miles (5
kilometers) wide is half-again as wide as New York's Manhattan Island .
Digging through the old data, Herrington found a map from 1932 and an aerial photo from
1933 that documented how, during a warm period, the Kangerdlugssuaq Glacier lost a piece
of floating ice that was nearly the size of New York 's Manhattan Island .
“That parallels what we know about recent changes,” Box said. “In 2002 to
2003, that same glacier retreated another 3.1 miles (5 kilometers), and that it tripled
its speed between 2000 and 2005.”
The fact that recent changes to Greenland's ice sheet mirror its behavior nearly 70 years
ago is increasing researchers' confidence and alarm as to what the future holds. Recent
warming around the frozen island actually lags behind the global average warming pattern
by about 1-2 degrees C but if it fell into synch with global temperatures in a few years,
the massive ice sheet might pass its “threshold of viability” – a tipping
point where the loss of ice couldn't be stopped.
“Once you pass that threshold,” Box said, “the current science suggests
that it would become an irreversible process. And we simply don't know how fast that might
happen, how fast the ice might disappear.”
Greenland 's ice sheet contains at least 10 percent of the world's freshwater AND it has
been losing more than 24 cubic miles (100 cubic kilometers) of ice annually for the last
five years and 2007 was a record year for glacial melting there.
This work was supported in part by the National Aeronautics and Space Administration, the
National Science Foundation and Ohio State.
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