Science for University Students. Part II. Translations. Сологуб Л.И. - 20 стр.

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Text 9
The Arctic: A Key to World Climate
The Arctic is part of a great -global heat engine. Changes in the arctic
atmosphere, ocean, sea ice, and permafrost are early precursors to climate
change elsewhere. In the past, those changes have been drastic. Only 18,000
years ago, virtually all of Canada and some of the United States were covered by
a thick layer of ice.
At the recent AAAS Annual Meeting, a symposium brought together some
of the leading research scientists active in studies of resources and climate. In
one of the sessions, speakers reviewed information about the evolution of the
arctic climate.
A principal impression that could be drawn from the symposium was that
the current hypothesis concerning effects of greenhouse gases on arctic behavior
is probably simplistic and may be quite wrong. The public has been told
repeatedly that a result of increased greenhouse gases would be a substantial rise
in sea level due to melting of polar ice. A related statement frequently made is
that the increase in polar temperatures would be substantially greater than those
of global averages. For example, one estimate is that an average rise of 2°C
would be accompanied by a 10°C increase in the Arctic. That estimate may or
may not adequately take into account climatic feedback mechanisms. At the
symposium this point was raised implicitly by John T. Andrews, who stated that
the Greenland Ice Sheet and the Laurentide Ice Sheet advanced during a period
of warm water influx into Baffin Bay at the end of the last interglaciation.
The vapor pressure of water is quite sensitive to temperature. Condensing
moisture in the form of snow provides a surface cover that highly reflects solar
energy leading to a regional cooling. The reflectivity of ordinary soil is about
0.1. The albedo of snow is about 0.8. At present, some of the arctic land areas
that have averaged annual temperatures of about - 14°C receive only 10
centimeters of total H
2
O per year. Most of the time the surface is bare and is a
good absorber of solar heat. Were more precipitation to occur, the total heat
absorbed by the surface would decrease. With greater moisture in the air, there
would be more clouds. The net effects of these are controversial. Some say that
more clouds would reflect more energy away from the earth. Others point out
that added moisture would enhance a greenhouse effect in the Arctic. In any
event, the factors controlling arctic climate are complex.
One of the obstacles to confidence in predicting the future of the arctic
climate is an imperfect knowledge of the past. We know that 70 million years
ago, the climate was mild and the Arctic Ocean was ice-free. Sediments formed
about 5 million years ago contained glacially related materials. We know little
about what happened in the long interval, and knowledge concerning more
recent events is sketchy. No long cores have been obtained from the Arctic
Ocean. The impediment is the perennial ice sheet that covers most of that ocean.
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