As reported in
FYI #163, on December 16 the American Geophysical Union released
a new position statement discussing the scientific evidence for human
impacts on global climate change. The text of the statement follows:
Human Impacts on Climate:
"Human activities are increasingly altering the Earth's climate.
These effects add to natural influences that have been present over
Earth's history. Scientific evidence strongly indicates that natural
influences cannot explain the rapid increase in global near-surface
temperatures observed during the second half of the 20th century.
"Human impacts on the climate system include increasing concentrations
of atmospheric greenhouse gases (e.g., carbon dioxide, chlorofluorocarbons
and their substitutes, methane, nitrous oxide, etc.), air pollution,
increasing concentrations of airborne particles, and land alteration.
A particular concern is that atmospheric levels of carbon dioxide may
be rising faster than at any time in Earth's history, except possibly
following rare events like impacts from large extraterrestrial objects.
"Atmospheric carbon dioxide concentrations have increased since
the mid-1700s through fossil fuel burning and changes in land use, with
more than 80% of this increase occurring since 1900. Moreover, research
indicates that increased levels of carbon dioxide will remain in the
atmosphere for hundreds to thousands of years. It is virtually certain
that increasing atmospheric concentrations of carbon dioxide and other
greenhouse gases will cause global surface climate to be warmer.
"The complexity of the climate system makes it difficult to predict
some aspects of human-induced climate change: exactly how fast it will
occur, exactly how much it will change, and exactly where those changes
will take place. In contrast, scientists are confident in other predictions.
Mid-continent warming will be greater than over the oceans, and there
will be greater warming at higher latitudes. Some polar and glacial
ice will melt, and the oceans will warm; both effects will contribute
to higher sea levels. The hydrologic cycle will change and intensify,
leading to changes in water supply as well as flood and drought patterns.
There will be considerable regional variations in the resulting impacts.
"Scientists' understanding of the fundamental processes responsible
for global climate change has greatly improved during the last decade,
including better representation of carbon, water, and other biogeochemical
cycles in climate models. Yet, model projections of future global warming
vary, because of differing estimates of population growth, economic
activity, greenhouse gas emission rates, changes in atmospheric particulate
concentrations and their effects, and also because of uncertainties
in climate models. Actions that decrease emissions of some air pollutants
will reduce their climate effects in the short term. Even so, the impacts
of increasing greenhouse gas concentrations would remain.
"The 1992 United Nations Framework Convention on Climate Change
states as an objective the "
stabilization of greenhouse gas
concentrations in the atmosphere at a level that would prevent dangerous
anthropogenic interference with the climate system." AGU believes
that no single threshold level of greenhouse gas concentrations in the
atmosphere exists at which the beginning of dangerous anthropogenic
interference with the climate system can be defined. Some impacts have
already occurred, and for increasing concentrations there will be increasing
impacts. The unprecedented increases in greenhouse gas concentrations,
together with other human influences on climate over the past century
and those anticipated for the future, constitute a real basis for concern.
"Enhanced national and international research and other efforts
are needed to support climate related policy decisions. These include
fundamental climate research, improved observations and modeling, increased
computational capability, and very importantly, education of the next
generation of climate scientists. AGU encourages scientists worldwide
to participate in climate research, education, scientific assessments,
and policy discussions. AGU also urges that the scientific basis for
policy discussions and decision-making be based upon objective assessment
of peer-reviewed research results.
"Science provides society with information useful in dealing with
natural hazards such as earthquakes, hurricanes, and drought, which
improves our ability to predict and prepare for their adverse effects.
While human-induced climate change is unique in its global scale and
long lifetime, AGU believes that science should play the same role in
dealing with climate change. AGU is committed to improving the communication
of scientific information to governments and private organizations so
that their decisions on climate issues will be based on the best science.
"The global climate is changing and human activities are contributing
to that change. Scientific research is required toimprove our ability
to predict climate change and its impacts on countries and regions around
the globe. Scientific research provides a basis for mitigating the harmful
effects of global climate change through decreased human influences
(e.g., slowing greenhouse gas emissions, improving land management practices),
technological advancement (e.g., removing carbon from the atmosphere),
and finding ways for communities to adapt and become resilient to extreme
Adopted by AGU Council, December, 2003