Geology Reference
In-Depth Information
further warming. On the other hand, in areas where climate warming results in increased
snow cover, albedo will also increase, leading to a reduction in atmospheric warming and
probably increased cloudiness. Finally, climate warming may advance the melt season
suffi ciently that seasonal-snow accumulations, which would have provided late-season
water sources for wetlands, may no longer exist. All these considerations make the impact
of climate warming upon the seasonal-snow cover diffi cult to predict.
15.3.2. Sea Ice and Sea Level
As the world's atmosphere and oceans become warmer, sea levels are expected to rise.
Projections by the Canadian Global Climate Model 1 indicate a rise in average global
sea level due to thermal expansion of approximately 40 cm by 2090 (Hengeveld, 2000).
Changes in the extent of the Greenland and Antarctic ice caps may also lead to a global
sea-level increase of between 0.5 m and 1.0 m over the next century. Of special concern to
periglacial environments will be the coastal lowlands that surround the Arctic basin in
the western North American Arctic and in Siberia. A climate-induced rise in sea level
will increase coastal erosion, fl ooding, and inshore marine sedimentation. There are sig-
nifi cant applied implications. Coastal communities will experience repeated fl ooding and
industrial structures built either at shoreline or offshore (drilling platforms and artifi cial
islands for offshore oil or gas production) will have to deal with changes in water depth,
shoreline confi guration, and sea-ice conditions.
Sea ice is perhaps the single most powerful positive feedback that will determine the
magnitude of global climate change in the coming century, particularly for the high north-
ern latitudes and much of northwestern Europe (Miller et al., 2001). There is a strong
possibility that the ice cover of the Arctic Ocean will disappear within the next 60-100
years. The US National Snow and Ice Data Center (NSIDC) reports that average surface
air temperatures in the Arctic are as much as 2-3 °C higher than 50 years ago. Satellite
records that extend back to 1978 indicate that the mean annual size of the Arctic ice cap
is shrinking at approximately 8% a year and measurements indicate the thickness of the
sea-ice cover has decreased by approximately 30% over the last 15 years. As sea ice is
already fl oating, when it melts it does not raise global sea level to any signifi cant extent.
However, the change in net albedo, the increased source of atmospheric moisture from an
ice-free ocean, and the consequent increase in cloudiness and precipitation will signifi -
cantly alter the climates and terrestrial environments of the high northern latitudes.
These changes will have mixed economic implications. Any reduction in thickness,
extent, and duration of Arctic sea ice would enhance coastal processes and shoreline
modifi cation, extend the shipping seasons along the Siberian, Alaskan, and Western
Canadian Arctic coasts, and make feasible a year-round Arctic shipping route from
Europe to Japan. Increased iceberg generation from Greenland tidewater glaciers would
possibly interfere with marine transportation in the northern North Atlantic and offshore
of eastern North America.
15.3.3. Gas Hydrates and Methane
Another important positive feedback related to the degradation of permafrost concerns
to gas hydrates and the release of methane (CH
4
) to the atmosphere.
Gas hydrates form where gas and water exist under high pressure and low
temperature. These conditions exist within and beneath permafrost where solid crystals
of gas hydrates can be found. Gas hydrates are a signifi cant and important form of
