The question of human impact has sparked intense debate from
the scientific community to the halls of Congress.
The focus in recent years has been on climate change models that
show a sharp increase in average temperature in the last 100 years
after a long period of stability -- creating a graph that looks
like a hockey stick.
model was incorporated into the international standard for assessment
of climate change, the Climate Change 2001 report produced by
the U.N. Intergovernmental Panel on Climate Change.
In 2005, 11 national science academies, including those from
the United States, United Kingdom, China and Russia, signed a
statement renewing their support for the document, asserting that
climate change is "real" and a result of human activities.
However, skeptics charge that the models forming the basis of
Climate Change 2001 haven't been sufficiently scrutinized.
A 2003 report criticized the simplicity of the mathematical models
used to create the "hockey stick" graph and suggested
using local data instead of global averages. Skeptics say other
climate change indicators account for local temperature anomalies
like a Medieval Warm Period that occurred about 1,000 years ago
and a Little Ice Age that ended about 100 years ago.
In the U.S. Congress, Republican Representative Joe Barton of
Texas, the chairman of the House Committee on Energy and Commerce,
condemned the "hockey stick" research and asked for
the raw data and a review of the methodology behind it.
This spurred a passionate response from the National Academies
of Sciences, National Science Foundation and 20 scientists, who
wrote to Barton supporting the validity of the research and its
One of those researchers was James Hansen, NASA's leading climate
scientist, who has pointed to ocean warming as the "smoking
gun" for global warming. Last year, he concluded that temperatures
could rise by 5 degrees Celsius over the next century. Hansen
has accused the federal government of censoring him and NASA documents
to align with policy.