Global Warming
By Holli Riebeek
Design by Robert Simmon
June 3, 2010
Throughout its long history, Earth has warmed and cooled time and
again. Climate has changed when the planet received more or less
sunlight due to subtle shifts in its orbit, as the atmosphere or surface
changed, or when the Sun’s energy varied. But in the past century,
another force has started to influence Earth’s climate: humanity
Previous versions of this article were published in
2007 and
2002. Archived versions are available as PDF files.
Global warming is the unusually rapid increase in Earth’s average
surface temperature over the past century primarily due to the
greenhouse gases released by people burning fossil fuels.
Earth has experienced climate change in the past without help from
humanity. But the current climatic warming is occurring much more
rapidly than past warming events.
In Earth’s history before the Industrial Revolution, Earth’s
climate changed due to natural causes unrelated to human activity. These
natural causes are still in play today, but their influence is too
small or they occur too slowly to explain the rapid warming seen in
recent decades.
Models predict that as the world consumes ever more fossil fuel,
greenhouse gas concentrations will continue to rise, and Earth’s average
surface temperature will rise with them. Based on plausible emission
scenarios, average surface temperatures could rise between 2°C and 6°C
by the end of the 21st century. Some of this warming will occur even if
future greenhouse gas emissions are reduced, because the Earth system
has not yet fully adjusted to environmental changes we have already
made.
The impact of global warming is far greater than just increasing
temperatures. Warming modifies rainfall patterns, amplifies coastal
erosion, lengthens the growing season in some regions, melts ice caps
and glaciers, and alters the ranges of some infectious diseases. Some of
these changes are already occurring.
http://earthobservatory.nasa.gov/Features/GlobalWarming/
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