"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
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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