The US National Academies of Science, the National
Aeronautics and Space Administration (NASA), and the
National Oceanic and Atmospheric Administration
(NOAA), and many others, say that greenhouse gas
levels are rising due to human activities such as burning
fossil fuels and deforestation which are causing
significant climate changes including global warming,
loss of sea ice, glacier retreat, more intense heat waves,
stronger hurricanes, and more droughts. They contend
that climate change requires immediate international
action to prevent dire consequences.
The Heartland Institute, the Heritage Foundation, and
the American Association of Petroleum Geologists, and
many others, argue that human-generated greenhouse
gas emissions are too small to substantially change the
earth’s climate. They contend that our forests and
oceans are capable of absorbing these small increases,
and that 20th century warming has resulted from
natural processes including fluctuations in the sun's
heat and ocean currents. They say that global climate
change is based on bunk science and scare tactics.
Human activities release greenhouse gases such as
carbon dioxide (CO2), methane (CH4), and nitrous oxide
(NO2), into the atmosphere. As of Apr. 2010, CO2 levels
were 389 parts per million (ppm) - reportedly higher
than at any time in the last 650,000 years when levels
fluctuated between 180 and 300 ppm. [3] This rise took
place alongside a 20th century global temperature
increase of between 1°F and 1.4°F.[ 1][ 43]
Although there was a period of cooling from 1940 to
1970 [ 2], and uncertainty exists in computer climate
models, [ 8] many researchers think the earth will
continue to warm by 3-10°F [ 1] over the 21st century.
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