CLIMATE COLLAPSE by David Stipp at www.fortune.com
- CLIMATE COLLAPSE
Growing Evidence of Scary Change
By David Stipp
Scientists used to think that major climate changes, like the onset
of an ice age, took thousands of years to unfold. Now they know such
dramatic transitions can occur in less than a decade. The probable
trigger of abrupt climate changes, at least in the Northern
Hemisphere, is the shutdown of a huge ocean current in the Atlantic
Ocean. The current is driven by dense, salty water that flows north
from the tropics and sinks in the North Atlantic. If fresh water is
pumped into the northerly part of the currentwhich can occur as
global warming melts Arctic iceits salinity drops, making it less
dense. This diminishing density can prevent the water from sinking in
the North Atlantic, stopping the current's flow. Much of Europe and
the U.S. could become colder and drier if that happened.
Many details of this big picture remain hazy, including whether
recent global warming threatens to shut down the Atlantic current.
But over the past few years, scientists have detected disquieting
In tandem with rising average temperatures across the globe, 3% to
4% of the Arctic ice cap has melted per decade since about 1970.
Recently the Arctic's largest ice shelf broke up near Canada's
Ellesmere Island, releasing an ice-dammed freshwater lake into the
ocean. (Scientists believe that the similar melting of an Arctic ice
dam 8,200 years ago triggered an episode of abrupt climate change.)
The North Atlantic's salinity has declined continuously for the
past 40 yearsthe most dramatic oceanic change ever measured.
The flow of cold, dense water through a North Atlantic channel near
Norwaypart of the great ocean current that warms northern Europehas
dropped by at least 20% since 1950, suggesting that the current is
Scientists still don't know whether a climate disaster is on the way.
But taken together, these changes appear strikingly similar to ones
that preceded abrupt climate shifts in the past. Many researchers now
believe the salient question about such change is not "Could it
happen?" but "When?"
From the Feb. 9, 2004 Issue