Climate Change: Science and Policy Implications
Excerpted from Congressional Research Service Report RL33849
Updated May 2, 2007
Jane A. Leggett
Specialist in Energy and Environmental Policy
Resources, Science, and Industry Division
Read the full report.
Almost all scientists agree that the Earth’s climate is changing, having warmed
by 0.6 to 0.9o Celsius (1.1 to 1.6o Fahrenheit) since the Industrial Revolution.
Science indicates that the Earth’s global average temperature is now approaching, or
possibly has passed, the warmest experienced since human civilizations began to
flourish about 12,000 years ago. During the 20th Century, some areas became wetter
while others experienced more drought. Most climate scientists conclude that
humans have induced a large part of the climate change since the 1970s. Although
natural forces such as solar irradiance and volcanoes contribute to variability,
scientists cannot explain the climate changes of the past few decades without
including the effects of elevated greenhouse gas (GHG) concentrations resulting from
fossil fuel use, land clearing, and industrial and agricultural emissions. Over the past
150 years, measured carbon dioxide concentrations have risen by more than onethird,
from about 280 parts per million (ppm) to about 380 ppm. The United States
contributes almost one-fifth of net global greenhouse gas emissions. Some impacts
of climate change are expected to be beneficial (e.g., increased agricultural
productivity in some regions), whereas others are expected to be adverse (e.g.,
drought in some regions, rising sea levels in some coastal areas).
Forecasting future climate conditions is challenging, and some major processes
remain poorly understood. However, methods are improving to characterize the
risks. Scientists have found it is very likely that rising greenhouse gas
concentrations, if they continue unabated, will raise the global average temperature
above natural variability by at least 1.5o Celsius (2.7o Fahrenheit) during the 21st
Century (above 1990 temperatures), with a small likelihood that the temperature rise
may exceed 5oC (9oF). The projections thought most likely by many climate
modelers are for a greenhouse gas-induced temperature rise of approximately 2.5 to
3.5oC (4.5 to 6.3oF) by 2100. However, the magnitude, rapidity, and details of the
change are likely to remain unclear for some time. Future climate change may
advance smoothly or sporadically, with some regions experiencing more fluctuations
in temperature, precipitation, and frequency or intensity of extreme events than
others. Some scientists emphasize potential beneficial effects of climate change, or
count on the ability of humans to adapt their behaviors and technologies to manage
climate change in the future; other scientists argue that the benefits of climate change
may be limited, even accounting for probable adaptation and its costs, and that there
are risks of abrupt, surprising change with accompanying dislocations.
The continuing scientific process has resulted in a better understanding of
climate change and generally confirms the broad conclusions made in previous
decades by the preponderance of scientists: that human activities emit greenhouse
gases that influence the climate, with potentially serious effects. Details have been
revised or refined, but the basic conclusion of the risks persists. The principal
questions remaining for the majority of scientists concern not whether greenhouse
gases will result in climate change, but the magnitude, speed, geographic details, and
likelihood of surprises, and the appropriate timing and options involved in addressing
the human components of climate change.
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The National Resource Defense Council (NRDC) has put out an issue summary for the McCain-Lieberman Climate Act as well as all a comparison of climate change legislation introduced in the 110th Congress.
[1] On Apr 24, 2008 Representative Dave Reichert gave a press release to clarify his his global warming legislation.
[2] On Aug 8, 2007 Representative Nick Lampson gave a press release addressing the need for Air and Water Pollution Control Facilities.
[3] On August 6, 2007 Representative Heath Shuler put out a press release regarding energy independence and climate change.
[4] On August 1, 2007 Representative Ciro Rodriguez put out a press release supporting Renewable Electricity Standard.
