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11.
Global
warming
“Global
warming” has been introduced by the scientific community and the media as the
term that encompasses all potential changes in climate that result from higher
average global temperatures. Hundreds of scientists from many different
countries are working to understand global warming and have come to a consensus
on several important aspects. In general, Global warming will produce far more
profound climatic changes than simply a rise in global temperature.
An analysis of temperature records shows that
the Earth has warmed an average of 0.5°C over the past 100 years. This is
consistent with predictions of global warming due to an enhanced greenhouse
effect and increased aerosols. Part of the current global warmth is associated
with the tropical El Nino, without which a record global temperature would
probably not have occurred.
The Earth's
climate is the result of extremely complex interactions among the atmosphere,
the oceans, the land masses, and living organisms, which are all warmed daily
by the sun's energy. This heat would radiate back into space if not for the
atmosphere, which relies on a delicate balance of heat-trapping gases -
including water vapor, carbon dioxide, nitrous oxide, and methane - to act as a
natural "greenhouse," keeping in just the right amount of the sun's
energy to support life.
For the past 150 years, though, the atmospheric concentrations of
these gases, particularly carbon dioxide, have been rising. As a result, more heat
is being trapped than previously, which in turn is causing the global
temperature to rise. Climate scientists have linked the increased levels of
heat-trapping gases in the atmosphere to human activities, in particular the
burning of fossil fuels (coal, oil, and natural gas for heating and
electricity; gasoline for transportation), deforestation, cattle ranching, and
rice farming.
As the Earth's climate is the result of extremely complex
interactions, scientists still cannot predict the exact impact on the earth's
climate of these rising levels of heat-trapping gases over the next century. The current best estimate is that if carbon dioxide
concentrations double over preindustrial levels, according to the scientific
possible scenarios, an atmospheric doubling of carbon dioxide could occur as
early as 2050.
In 1995, scientists with the
Intergovernmental Panel on Climate Change - the authoritative international
body charged with studying this issue-reached a conclusion in the Second Assessment Report, which summarizes the current
state of scientific knowledge on global warming, also called climate change.
For the first time ever, the Panel concluded that the observed increase in
global average temperature over the last century "is unlikely to be
entirely natural in origin" and that "the balance of evidence
suggests that there is a discernible human influence on global climate."