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NSF
PR 03-129 - December 2, 2003
Top
Scientists Conclude Human Activity is Affecting Global Climate
Arlington,
Va.—Two of the nation's best-known atmospheric scientists,
after reviewing extensive research by their colleagues, say there is no
doubt human activities are having measurable—and increasing—impacts on global climate. Results of the
study, which appears in the December 5th issue of the journal Science as part of a "State of
the Planet" assessment, cites atmospheric observations and multiple
computer models to paint a detailed picture of the climate changes likely
to buffet Earth in coming decades, including rising temperatures and an
increase in extreme weather events such as flooding.
Thomas Karl of NOAA's National Climatic Data
Center in Asheville, N.C., and Kevin Trenberth,
director of the Climate Analysis Section at the National Center for
Atmospheric Research (NCAR) in Boulder, Colo., conclude that industrial
emissions have been the dominant influence behind climate change for the
past 50 years, overwhelming natural forces. The most important of these
emissions is carbon dioxide, a greenhouse gas that traps solar radiation
and warms the planet. Trenberth's research is
funded by the National Science Foundation (NSF), the independent federal
agency that supports fundamental research and education across all fields
of science and engineering.
"There is no doubt the composition of the atmosphere is changing
because of human activities, and today greenhouse gases are the largest
human influence on global climate," they write. "The likely
result is more frequent heat waves, droughts, extreme precipitation events,
and related impacts, e.g., wildfires, heat stress, vegetation changes, and
sea-level rise which will be regionally dependent."
"Many important climate research accomplishments over the past
several decades have led to major improvements in understanding and
predicting our climate," said Jay Fein, director of NSF's climate
dynamics program. "Karl and Trenberth
summarize those accomplishments in terms of what we have learned about our
climate and the many factors that force it. As they point out, however,
there still remain important uncertainties, both in terms of climate
forcing and climate response. Addressing the uncertainties will require
continuing research and model development, underpinned by high-quality,
long-term global environmental observations and social and economic
data."
Karl and Trenberth estimate that, between 1990
and 2100, global temperatures will rise by 1.7°C to 4.9°C (3.1°F-8.9°F).
The increase would have widespread impacts on society and the environment,
including melting the great ice sheets of Greenland and Antarctica and inundating
the world's coasts. The authors base their estimate on computer model
experiments by a number of climate scientists, observations of atmospheric
changes and recorded climate changes over the past century.
Carbon dioxide levels in the atmosphere have risen by 31 percent since
pre-industrial times-from 280 parts per million by volume (ppmv) to over 370 ppmv today.
Other human activities, such as emissions of sulfate and soot particles and
the development of urban areas, have significant but more localized climate
impacts. Such activities sometimes cause temperatures to rise or fall, but
not by enough to offset the impact of greenhouse gases.
If societies successfully cut emissions and stabilized carbon dioxide
levels in the atmosphere, temperatures would still increase by an estimated
0.5°C over a period of decades, Karl and Trenberth
warn. This is because greenhouse gases are slow to cycle out of the
atmosphere. "Given what has happened to date and is projected in the
future, significant further climate change is guaranteed," the authors
state.
If current emissions continue, the world would face the fastest rate of
climate change in at least the past 10,000 years. This could potentially
alter ocean current circulations and radically change existing climate
patterns. Moreover, certain natural processes would likely accelerate the
warming. As snow cover melts away, for example, the darker land and water
surface would absorb more solar radiation, further increasing temperatures.
Karl and Trenberth say more research is needed
to pin down both the global and regional impacts of climate change.
Scientists have yet to determine the temperature impacts of increased cloud
cover or how changes in the atmosphere will influence El Niño, the periodic warming of Pacific Ocean waters that
affects weather patterns throughout much of the world. The authors call for
multiple computer model studies to address the complex aspects of weather
and climate. The models must be able to integrate all components of Earth's
climate system-physical, chemical and biological. This, in turn, will
require considerable international cooperation and establishment of a
global climate monitoring system to collect data.
"Climate change is truly a global issue, one that may prove to be
humanity's greatest challenge," the authors conclude.
The National Science Foundation
(NSF) is an independent federal agency that supports fundamental research
and education across all fields of science and engineering, with an annual
budget of nearly $5.3 billion. NSF funds reach all 50 states through grants
to nearly 2,000 universities and institutions. Each year, NSF receives
about 30,000 competitive requests for funding, and makes about 10,000 new
funding awards. The NSF also awards over $200 million in professional and
service contracts yearly.
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