Global warming is the observed increase in the
average temperature of the Earth's atmosphere and oceans in recent
decades and its projected continuation into the future. The decade
of 2001-2009 was the warmest decade recorded on earth.
Global average near-surface atmospheric temperature rose 0.6 ± 0.2
°Celsius (1.1 ± 0.4 °Fahrenheit) in the 20th century. The prevailing
scientific opinion on climate change is that "most of the warming
observed over the last 50 years is attributable to human
activities." The main cause of the human-induced component of
warming is the increased atmospheric concentration of greenhouse
gases (GHGs) such as carbon dioxide (CO2), which leads to warming of
the surface and lower atmosphere by increasing the greenhouse
effect. Greenhouse gases are released by activities such as the
burning of fossil fuels, land clearing, and agriculture.
Models referenced by the Intergovernmental Panel on Climate Change (IPCC)
predict that global temperatures may increase by 1.4 to 5.8 °C (2.5
to 10.5 °F) between 1990 and 2100. The uncertainty in this range
results from both the difficulty of predicting the volume of future
greenhouse gas emissions and uncertainty about climate sensitivity.
An increase in global temperatures can in turn cause other changes,
including a rising sea level and changes in the amount and pattern
of precipitation. These changes may increase the frequency and
intensity of extreme weather events, such as floods, droughts, heat
waves, hurricanes, and tornados. Other consequences include higher
or lower agricultural yields, glacier retreat, reduced summer
streamflows, species extinctions and increases in the ranges of
disease vectors. Warming is expected to affect the number and
magnitude of these events; however, it is difficult to connect
particular events to global warming. Although most studies focus on
the period up to 2100, even if no further greenhouse gases were
released after this date, warming (and sea level) would be expected
to continue to rise since CO2 has a long average atmospheric
lifetime.
Remaining scientific uncertainty comes from the exact degree of
climate change expected in the future and particularly how changes
will vary from region to region across the globe. In addition, the
complexity of the earth's climate complicates the understanding and
forecasting of the effects of climate change. For example, changes
in water vapor in the earth's atmosphere is believed to have
cancelled roughly 25% of the global warming caused by carbon
emissions during the past decade.Most national governments have
committed to taking steps to mitigate future climate change.
Read more about Climate Change from the U.S. Environmental
Protection Agency
National Oceanic and Atmospheric Administration: GW Frequently Asked
Questions
New York Times Global Warming Coverage
New Scientists Guide to Climate Change
Pew Center on Global Climate Change
Climate Change: American Museum of Natural History |
