Q. What is climate change?
A. Climate is the average meteorological
conditions—temperature, precipitation, wind, etc.—that
prevail in a region. Climate
change may refer to any change in climate over time
whether due to natural variability or human activity.
Three major sources of natural variability affect climate:
changes in Earth's orbit, changes in ocean currents due
to shifting continents or large-scale melting of continental
ice, and changes in the composition of the global atmosphere—especially
water vapor and "greenhouse" gases such as carbon dioxide
(CO2), methane (CH4),
and nitrous oxide (N2O)—due to volcanic
or other tectonic activities. The term "greenhouse" refers
to the ability of these gases to absorb energy radiated
from Earth to space and to thus warm the atmosphere.
Human activity may also influence the composition of the global
atmosphere. As of 1992, for example, atmospheric
concentrations of CO2, CH4, and N2O
had grown by about 30 percent, 145 percent, and 15 percent since
pre-industrial times (about 1750). Major sources include combustion
of fossil fuel, deforestation, and production of some agricultural
commodities such as rice and livestock. Since the late 19th century,
anthropogenic emissions of CO2, CH4, and
N2O have been associated with an overall increase in
global mean surface air temperature between about 0.3 and 0.6°C
(about 0.5 and 1.1°F).
In 1996, the Intergovernmental Panel on Climate Change (IPCC),
which organizes, summarizes, and reports the work of several hundred
scientists, released its second assessment report, which concluded
that "...the balance of evidence suggests that there is a discernible
human influence on global climate" (IPCC, 1996). The IPCC
also reported that, relative to 1990, global mean surface air temperature
could be 1.0 to 3.5°C (about 1.8 to 6.3°F) higher by 2100.
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