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Science Forum Index » Environment Forum » AGU statment on Human Impacts on Climate
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| Jim Norton |
 Posted: Tue Dec 16, 2003 9:51 pm |
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http://www.agu.org/sci_soc/policy/climate_change_position.html
Human Impacts on Climate
Adopted by Council December, 2003
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 to improve 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 events.
====================================================
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