How Global Warming May Cause the Next Ice Age...

by Thom Hartmann

While global warming is being officially ignored by the political arm 
of the Bush administration, and Al Gore's recent conference on the 
topic during one of the coldest days of recent years provided joke 
fodder for conservative talk show hosts, the citizens of Europe and 
the Pentagon are taking a new look at the greatest danger such 
climate change could produce for the northern hemisphere - a sudden 
shift into a new ice age. What they're finding is not at all 
comforting.

In quick summary, if enough cold, fresh water coming from the melting 
polar ice caps and the melting glaciers of Greenland flows into the 
northern Atlantic, it will shut down the Gulf Stream, which keeps 
Europe and northeastern North America warm. The worst-case scenario 
would be a full-blown return of the last ice age - in a period as 
short as 2 to 3 years from its onset - and the mid-case scenario 
would be a period like the "little ice age" of a few centuries ago 
that disrupted worldwide weather patterns leading to extremely harsh 
winters, droughts, worldwide desertification, crop failures, and wars 
around the world.

Here's how it works.

If you look at a globe, you'll see that the latitude of much of 
Europe and Scandinavia is the same as that of Alaska and 
permafrost-locked parts of northern Canada and central Siberia. Yet 
Europe has a climate more similar to that of the United States than 
northern Canada or Siberia. Why?

It turns out that our warmth is the result of ocean currents that 
bring warm surface water up from the equator into northern regions 
that would otherwise be so cold that even in summer they'd be covered 
with ice. The current of greatest concern is often referred to as 
"The Great Conveyor Belt," which includes what we call the Gulf 
Stream.

The Great Conveyor Belt, while shaped by the Coriolis effect of the 
Earth's rotation, is mostly driven by the greater force created by 
differences in water temperatures and salinity. The North Atlantic 
Ocean is saltier and colder than the Pacific, the result of it being 
so much smaller and locked into place by the Northern and Southern 
American Hemispheres on the west and Europe and Africa on the east.

As a result, the warm water of the Great Conveyor Belt evaporates out 
of the North Atlantic leaving behind saltier waters, and the cold 
continental winds off the northern parts of North America cool the 
waters. Salty, cool waters settle to the bottom of the sea, most at a 
point a few hundred kilometers south of the southern tip of 
Greenland, producing a whirlpool of falling water that's 5 to 10 
miles across. While the whirlpool rarely breaks the surface, during 
certain times of year it does produce an indentation and current in 
the ocean that can tilt ships and be seen from space (and may be what 
we see on the maps of ancient mariners).

This falling column of cold, salt-laden water pours itself to the 
bottom of the Atlantic, where it forms an undersea river forty times 
larger than all the rivers on land combined, flowing south down to 
and around the southern tip of Africa, where it finally reaches the 
Pacific. Amazingly, the water is so deep and so dense (because of its 
cold and salinity) that it often doesn't surface in the Pacific for 
as much as a thousand years after it first sank in the North Atlantic 
off the coast of Greenland.

The out-flowing undersea river of cold, salty water makes the level 
of the Atlantic slightly lower than that of the Pacific, drawing in a 
strong surface current of warm, fresher water from the Pacific to 
replace the outflow of the undersea river. This warmer, fresher water 
slides up through the South Atlantic, loops around North America 
where it's known as the Gulf Stream, and ends up off the coast of 
Europe. By the time it arrives near Greenland, it's cooled off and 
evaporated enough water to become cold and salty and sink to the 
ocean floor, providing a continuous feed for that deep-sea river 
flowing to the Pacific.

These two flows - warm, fresher water in from the Pacific, which then 
grows salty and cools and sinks to form an exiting deep sea river - 
are known as the Great Conveyor Belt.

Amazingly, the Great Conveyor Belt is only thing between comfortable 
summers and a permanent ice age for Europe and the eastern coast of 
North America.

Much of this science was unknown as recently as twenty years ago. 
Then an international group of scientists went to Greenland and used 
newly developed drilling and sensing equipment to drill into some of 
the world's most ancient accessible glaciers. Their instruments were 
so sensitive that when they analyzed the ice core samples they 
brought up, they were able to look at individual years of snow. The 
results were shocking.

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