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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 Printed on recycled paper using vegetable based inks © UCS July 2009. 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 Printed on recycled paper using vegetable based inks © UCS July 2009.