Geoscience Reference
In-Depth Information
lieve that the current models of glacier disintegration do not fully capture
the dynamics, and that the rise may occur much more rapidly. Scientists
are hard at work modeling these changes, and it seems likely that the
pace and scope of ice sheet melting will be better understood in the com-
A second important singularity is change in ocean currents, par-
ticularly the Atlantic thermohaline circulation, popularly known as the
Gulf Stream. In the present era, the Gulf Stream carries warm surface
water to the North Atlantic. As a result, North Atlantic communities are
much warmer than their latitude would indicate. For example, Scotland
is at the same latitude as the peninsula of Kamchatka in far eastern Rus-
sia, but the average temperature in Scotland is about 12°C (22°F) warmer
than in Kamchatka.
Although the Gulf Stream has been stable for several thousand
years, it appears that large and rapid shifts occurred in earlier times,
particularly during ice ages. The Gulf Stream has even switched direc-
tion on several occasions. A reversal of the Gulf Stream would lead to a
steep temperature decline in the North Atlantic region as it would no
longer bring a fl ow of warm water to the north.
Currently, as the warm surface waters of the Gulf Stream move
north, they release their heat in the North Atlantic region, with the re-
sult that communities there are pleasant for humans and other living
things. As the water fl ows north, it cools and becomes denser. At some
point, the cooler dense water sinks, and then moves back south as if on
a conveyor belt.
What would lead to a shift in the fl ow of the Gulf Stream? In a
warmer world, the conveyor belt can get disrupted. This would happen
because of increases in both temperature and (freshwater) precipitation
at higher latitudes. These changes would make surface water less dense
because salt water is denser than fresh water. The sinking process would
weaken and reduce the speed of the conveyor belt—or might even
cause it to stop and reverse. This process would tend to cool the North
Atlantic relative to the rest of the world.
The most recent studies indicate that the Gulf Stream is likely to
weaken over the next century. However, expert assessments indicate
