Two things are uncertain. First, it is not yet clear what has
caused global warming so far. Has it occurred because human activities
have added to the "greenhouse gases" in the atmosphere?
Or has it resulted from natural temperature fluctuations? Second,
nobody knows precisely how much the world will warm for a given
amount of added greenhouse gases. Much hinges on socalled "feedbacks"
how the planet itself responds to being warmed up.
The greenhouse effect is no myth. It is a natural feature of the
atmosphere. Certain gases, such as water vapour, carbon dioxide
(CO2), and methane, are called "greenhouse gases" because
they trap solar heat in the lower atmosphere. Without them, Earth
would be frozen.
But humans are adding to these gases, producing pollutants that
cause a gas buildup in the atmosphere. Most important of these
human contributions is CO2, which is given off whenever we burn
carboncontaining materials, such as coal, oil, or wood. CO2 remains
in the atmosphere on average for more than a century. Over the
past 200 years, its concentration in the air has risen by a third,
largely because growing populations have burnt more trees and
failed to replace them and because they have begun to burn massive
quantities of fossil fuels.
If we carry on as we are, there will be twice as much CO2 in the
atmosphere by late next century. And the heating power of the
sun at the earth's surface will rise by about 4 watts per
square metre to 240 watts. Not a lot, you might think. But it
will raise temperatures directly by an average 1°C.
What is uncertain is how much the changes in the planet caused
by warming will themselves amplify that warming. Most solar heat
reaching polar regions is reflected from the white ice right back
into space. If we melt some of the ice caps, less heat will be
reflected. Likely result: a warmer Earth. Global warming will
also evaporate more water from the oceans into the air. Water
vapour is the most important greenhouse gas of all. So again,
extra warming is likely.
- The Climate Convention
- Developing Countries
- Looking For Loopholes
POLAR WARNINGS
Scientists have warned for some time that the polar regions may
be the first to show signs of global warming just as they were
for the thinning ozone layer. Some of the most persuasive evidence
that warming is already occurring here comes from the British
research bases in Antarctica that first spotted the Antarctic
ozone hole a decade ago.
In mid 1994, the British Antarctic Survey (BAS) reported that,
over the past 40 years, average temperatures in the peninsular
region of West Antarctica had risen by.5°C 10 times the
global average. BAS scientists believe the drastic warming may
be a consequence of the breakup of ice sheets in the region,
a classic example of the positive feedbacks to global warming
predicted by climate modelers. The Wardie ice shelf near the
peninsula has shrunk by more than 1,000km2 in the past 25 years.
The warming is most intense in West Antarctica. Here, researchers
warn, the ice sheet is precariously perched on top of submerged
islands and could suddenly disintegrate. The disappearance of
the West Antarctic ice sheet would raise sea levels worldwide
by an estimated 6m.
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