Environmental Engineering Reference
In-Depth Information
In December 2005, researchers at the National Oceanography Centre
in the United Kingdom reported that the Gulf Stream slowed by about
30 percent between 1957 and 2004.
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This has had no known effect on
temperatures in Western Europe. Early in 2006, a senior researcher at
the Ocean Physics Laboratory in France said that the changing climate
could slow the Gulf Stream by 25 percent by the year 2100.
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Clearly
we are in uncharted territory when considering modifi cations of ocean
currents.
Permafrost
Permafrost is defi ned as ground perennially frozen for more than two
years. It is present at high latitudes and, to a lesser degree, at high eleva-
tions. Permafrost covers an area slightly smaller than South America and
extends across a quarter of the Northern Hemisphere to depths of 1,000
feet or more. Sixty percent of Russia and 42 percent of Canada are
covered by permafrost. It is present beneath the Arctic Ocean as well as
on land. Most of the world's permafrost has been in this condition for
thousands of years.
The southern boundary of permafrost, now generally located between
55ºN and 60ºN latitudes in Canada, Alaska, and Siberia, has been
migrating northward in response to global warming. As recent warming
trends continue and perhaps accelerate, the area covered by permafrost
will continue to decrease. Glaciologists estimate that it will take several
centuries for all of it to disappear, but such estimates are as uncertain
as the melting rates of Antarctica and Greenland.
Recent warming has degraded large sections of permafrost across
central Alaska, with pockets of soil collapsing as the ice within it melts.
There is damage to construction founded on ice-rich permafrost, such as
buckled roads and bridges, airports, destabilized houses, damaged pipe-
lines, and “drunken forests”—trees that lean at wild angles. In Siberia,
some industrial facilities have reported signifi cant damage. Thawing
permafrost is sending large amounts of water to the oceans. Runoff to
the Arctic Ocean has increased about 7 percent since the 1930s.
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There is concern about emissions of greenhouse gases from thawing
soils. Permafrost may hold 30 percent or more of all the carbon stored
in soils worldwide. Thawing permafrost could lead to large-scale emis-
sions of carbon dioxide or methane beyond those produced by fossil
fuels. Decomposition of organic matter in contact with atmospheric
oxygen will produce carbon dioxide; organic matter in water-saturated
