May 8, 2006
Presently, there
is growing and compelling evidence that the Earth's surface is getting warmer.
In particular, it is warmer today than it was a century ago. Sea surface
temperatures, for example, are running about 1 to 2 degrees Centigrade
(approximately 1.8 to 3.6 degrees Fahrenheit) above normal. There have been two
relatively rapid periods of temperature increases, one between 1910 and 1940, and the other
between 1960 and today.
Many scientists believe the current trend of global warming is one of the
greatest environmental threats facing humanity, next to a nuclear cataclysm.
For instance, climate warming could accelerate the melting of the West
Antarctic Ice Sheet (anchored in the ocean below sea level) and of the Greenland
Ice Cap. The resulting rise in sea level over the next century could threaten
major coastal communities. The implications of the current phase of global
warming for modern civilization could be very serious, even though all its
damaging effects remain to be fully ascertained.
Because so many forces influence the Earth's climate, there is still
some uncertainty about the relative importance of each set of causes behind the
current observed climate warming. For example, some scientists estimate that
part of the trend in Earth's warming could be caused by natural factors acting
within a very long cycle, such as a recurring closer proximity of the Earth to
the Sun, the
star that supplies our planet with heat and energy. The remaining observed
warming is attributed to human-made pollution, such as the release of carbon
dioxide (CO2) gas into the
atmosphere.
It appears that human-made pollution of the atmosphere is already
having a serious affect on the Earth's climate and on the Earth's ecological
system. On the one hand, human activities over the past 100 years, such as the
burning of fossil fuel (coal, oil, natural gas, etc.) have contributed to
creating 'global warming'. It is because the greenhouse gases
that result from fossil fuel consumption insulate the Earth's atmosphere and
prevent the Earth's heat from escaping into space, causing surface air temperatures
and sub-surface ocean temperatures to rise. Greenhouse gases in the atmosphere absorb infrared radiation, thereby
preventing some of the outgoing energy from returning to space. As a result,
the Earth's atmosphere gets warmer.
On the other hand, the same human-made air pollutants caused by fossil
fuel use, and which result in the visible layers of smog that can be seen in
the atmosphere, make clouds that reflect more of the sun’s rays back into
space. This leads to a contrary effect known as 'global dimming',
whereby less heat and energy from the Sun reaches the Earth. As a result of the
Earth receiving less sunlight, there is a global cooling effect on land and the
oceans. This has influenced the occurence and patterns of rainfalls in some
regions of the globe, causing droughts and famine in these areas, especially in
the Northern Hemisphere mid-latitudes. It has been postulated that the failure
of the monsoon in sub-Saharan Africa during the 1970s and 1980s may have been
caused by 'global dimming'.
The Earth's climate seems to be caught in a sort of tug-of-war between
two competing atmospheric effects: One kind of pollution prevents sunlight from
reaching the Earth, while another one prevents the radiation of heat from the
Earth from escaping into space. The global cooling effects of air pollution
with visible particles thus tend to mask somewhat the global warming effects of
invisible greenhouse gases. However, scientists have estimated that over the
last few decades, the global warming effects of pollution have been stronger
than its cooling effects. Without the cooling effects of pollution, indeed, the
Earth's surface temperature would have risen by about 1.8 degree Centigrade
(about 3 degrees Fahrenheit), over the last few decades. But, because of the
cooling effect of "global dimming', estimated at around 1 degree
Centigrade (less than 1.5 degrees Fahrenheit), the Earth's average temperature
only rose between 0.6 and 0.8 degrees Centigrade.
This poses a potentially difficult dilemma regarding the fight against atmospheric pollution.
Indeed, if there is less visible pollution in the air at the same time that
greenhouse gas emissions keep augmenting, a reduction in global dimming effects
would tend to exacerbate global warming. Thus, paradoxically, a rapid solution
to global dimming may lead to more pronounced increases in the Earth's temperature.
The ice caps at the Earth's poles would risk melting at a faster rate and the
level of oceans could rise faster, with all the consequences that such
occurrences could entail for low sea-level inhabited regions and for the global
ecological system. The obvious but difficult solution would consist in reducing
simultaneously both visible (particles) pollution and invisible (greenhouse
gases) pollution. This will be the mounting challenge facing humanity in the
coming decades.
Whether we like it or not, humans are now a significant part of the
Earth climate system and this means that they can do something to influence it
in the right direction, or, at least, slow its advance in the wrong direction.
Humans have to pay attention to the environment and to the global life support
system. We need more scientific understanding of the Earth as a complex system
and more enlightened international collaboration to face the new challenges
that global pollution presents. The current generation of humans has no right to
leave a damaged and depreciated environment to future generations.
Meanwhile, let us deplore that American scientists are being prevented by the Bush administration from
speaking forthrightly to the public about global warming and other pollution
topics. We need more debate on this issue, not less. In a democracy,
intimidation and censorship are inherently dangerous. As one scientist put it,
this "seems more like Nazi Germany or the Soviet Union than the United
States." The more so, knowing full well that the United States is the world's biggest polluter.
Posted by Rodrigue Tremblay, May
8, 2006, at 9:00 am
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