Download Global Warming: Frequently Asked Questions

Global Warming:
Frequently Asked Questions
FACT SHEET
SCIENTIFIC CONSENSUS, URGENCY, SCIENTIFIC CONTRARIANS, U.S. AND WORLD ACTION
Scientists agree that excess carbon dioxide from burning
gas, burning coal and destroying forests is the main driver
of global warming. Global warming is happening more
quickly than anticipated and emissions today will lock in
future warming for centuries. Scientific contrarians don’t
represent the consensus opinion of scientists or the
scientific literature. Science indicates that deep emissions
reductions are needed to prevent the worst consequences
of climate change.
What Scientists Say
Scientists conclude that global temperatures have increased
more than 1 degree Fahrenheit during the past century.
During that time, the accumulation of excess carbon
dioxide and other heat-trapping gases in the atmosphere -primarily from burning coal, gas and destroying forests -has been the largest change to the Earth’s climate. Changes
in the Earth’s orbit, the Sun’s power and the changing
positions of the continents have had dramatic effects on
the Earth’s climate over tens-of-thousands and hundredsof-thousands of years. Like car mechanics diagnosing an
engine noise, scientists have eliminated variables that drive
temperatures up and down and concluded that excess
carbon dioxide and other heat-trapping gases are the only
reasonable explanation for most of the observed warming.
collaboration of 13
“Global warming is
federal agencies also
unequivocal and primarily
shares this view. Their
human-induced.”
2009 report states,
– US Global Change Research
“Global warming is
Program (2009)
unequivocal and
primarily humaninduced. Global temperature has increased over the past
50 years. This observed increase is due primarily to
human-induced emissions of heat-trapping gases.”i No
scientific body in the world disputes the basic premise that
human activity is driving global warming.
Urgency
Human Activities and Natural Factors are Needed to
Explain Recent Warming
Recent warming also matches the pattern scientists expect
from gases building up like a heat-trapping blanket around
the Earth. In particular, the boundary between the two
layers of the atmosphere directly above the land has
shifted upward over the past 20 years. Such a shift could
only result from heat-trapping gases building up in the
atmosphere. If other factors, such as solar radiation, were
at work, we would expect to see a different heating pattern
in the atmosphere.
Major scientific bodies endorse the basic hypothesis, first
articulated more than two centuries ago, that excess carbon
dioxide drives global warming. They include: the National
Academy of Sciences, the American Meteorological
Organization and the American Geophysical Union. The
United States Global Climate Research Project, a
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Carbon dioxide stays in the atmosphere for a long time.
About 20 percent of excess carbon dioxide emitted today
will still exist in the atmosphere approximately 800 years
from now.ii Additionally, the Earth’s ability to absorb
excess carbon dioxide, primarily through the ocean, is
diminishing.iii Additional scientific evidence indicates that
the Earth is responding more rapidly to temperature
increases than scientists have projected.
CO2’s long life in the atmosphere provides the clearest
possible rationale for reducing our CO2 emissions without
delay. We do not have time to “wait and see” before taking
action because the emissions we put into the atmosphere
today are locking in warming for future generations.
systems risk crossing dangerous thresholds at around 2
degrees Fahrenheit above today’s temperatures. Working
backward from that temperature target, climate science can
tell us the probability of exceeding such a temperature
threshold based on current and future carbon dioxide
emissions. A conservative estimate indicates that we would
have a 50/50 chance of coming in under that threshold if
we stabilized the atmospheric concentration of carbon
dioxide at 450 parts per million (ppm), up from today’s
380 ppm.iv Scientific evidence continues to indicate that a
lower atmospheric concentration target would be prudent
to prevent the worst consequences of global warming.
One recent paper put it more simply: the world can only
burn about half of its remaining gas and coal reserves to
meet such a target.v
Scientific Contrarians
While scientists are willing to update their views in light
of new evidence, many contrarians fail to do so. Many
individual contrarians and organizations have been using
the same discredited arguments for years. Other have
quietly shifted their arguments as their old positions on
the science lost credibility with the mainstream media
without acknowledging their previous errors. To explain
the scientific consensus that contradicts their views, they
often invoke conspiratorial thinking.
Scientific contrarian viewpoints are almost never found in
the scientific literature and no contrarian arguments have
withstood the test of scientific scrutiny. Therefore,
contrarian viewpoints are found almost exclusively in
non-scientific outlets such as talk radio and blogs. While
unanimity is almost unheard of in any scientific discipline,
the wide-spread consensus on human-induced climate
change is overwhelming.
What should the United States Do?
Climate science can inform emissions reductions targets
for 1) preventing a certain level of climate change 2)
reducing global emissions 3) reducing emissions for any
one country.
Other countries recognize that the United States must act
to make a global emissions reduction deal possible. An 80
percent reduction in emissions from today’s level by midcentury is a reasonable goal politically, economically and
scientifically. A strong short-term target, on the order of
35 percent below today’s levels is achievable for ensuring
flexbility in meeting a long-term emissions reduction goal.vi
i
http://www.globalchange.gov/publications/reports/scientific-assessments/usimpacts/key-findings
ii
Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J.
Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz
and R. Van Dorland, 2007: Changes in Atmospheric Constituents and in Radiative
Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of
Working Group I to the Fourth Assessment Report of the Intergovernmental Panel
on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B.
Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge,
United Kingdom and New York, NY, USA.
iii
Canadell, J.G., C. Le Quéré, M. R. Raupach, C. B. Field, E. T. Buitenhuis, P.
Ciais, T. J. Conway, N. P. Gillett, R. A. Houghton, and G. Marland. 2007.
Contributions to accelerating atmospheric CO2 growth from economic activity,
carbon intensity, and efficiency of natural sinks, Proceedings of the National
Academy of Sciences.
iv
http://www.ucsusa.org/global_warming/solutions/big_picture_solutions/a-targetfor-us-emissions.html
v
Meinshausen, M., N. Meinshausen, W. Hare, S.C.B. Raper, K. Frieler, R.
Knutti5, D. J. Frame and M. R. Allen. 2009. Greenhouse-gas emission targets for
limiting global warming to 2 °C, Nature 458:1158-1163. doi:10.1038/nature08017
vi
http://www.ucsusa.org/assets/documents/global_warming/Climate-2030Blueprint_executive-summary.pdf
Most scientists agree that sensitive human and natural
A fully referenced version of this fact sheet is available online at www.ucsusa.org/global-warming-faq.html
For more information, please contact Liz Perera,
Washington Representative at
[email protected] and 331-6948
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© UCS July 2009.