10 Topics for exams - topic3.



                                     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."

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