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U.S. Scientists and Economists’ Call for Swift and Deep Cuts in Greenhouse Gas Emissions - Letter

There is growing momentum in the United States to establish policies that cap and reduce our nation's heat-trapping emissions. A central feature of the policy debate—in Congress, in the international negotiations, and in statehouses and legislatures across the country—is over how swiftly and how deeply U.S emissions should be reduced.

A distinguished group of U.S. scientists and economists have come together to develop and endorse this Call for Swift and Deep Cuts in Greenhouse Gas Emissions. The core purpose is to ensure that this debate is informed by a powerful, succinct statement from top U.S. experts on the urgency of U.S. action, and the scale and feasibility of needed reductions.

The Union of Concerned Scientists is providing logistical support for this initiative on behalf of the signatories.

U.S. Scientists and Economists' Call for Swift and Deep Cuts in Greenhouse Gas Emissions

We call on our nation's leaders to swiftly establish and implement policies to bring about deep reductions in heat-trapping emissions. The strength of the science on climate change compels us to warn the nation about the growing risk of irreversible consequences as global average temperatures continue to increase over pre-industrial levels (i.e., prior to 1860). [1,2] As temperatures rise further, the scope and severity of global warming impacts will continue to accelerate.

The 2007 report of the Intergovernmental Panel on Climate Change [2] unequivocally concluded that our climate is warming, stating with at least 90 percent certainty that the warming of the last several decades is primarily due to human activities. Global average temperatures have already risen ~ 0.7°C (1.3°F) over the last 100 years, and impacts are now being observed worldwide. [1,2] Human-caused emissions to date have locked in further changes including sea-level rise that will intensify coastal flooding, and dramatic reductions in snowpack that will disrupt water supplies in the western United States. [1,3] If emissions continue unabated, our nation and the world will face more sea level rise, heat waves, droughts, wildfires, snowmelt, flood risk, and public health threats, as well as increased rates of plant and animal species extinctions. [1,4]

The longer we wait, the harder and more costly it will be to limit climate change and to adapt to those impacts that will not be avoided. Many emissions reduction strategies can be adopted today that would save consumers and industry money while providing benefits for air quality, energy security, public health, balance of trade, and employment. [5,6]

All nations must commit to a goal designed to limit further harm. The United States, the European Union, and a number of other countries have recognized the need for limiting global warming to no more than 2°C (3.6°F) above pre-industrial levels.[7]  Emerging science must be regularly evaluated to assess whether this goal is sufficient.

The UN Framework Convention on Climate Change recognizes that all nations have a responsibility to curb global warming, consistent with their respective contribution to emissions and capacity to act. Recent analyses indicate the United States—even with aggressive action by other nations—would need to reduce its emissions on the order of 80 percent below 2000 levels by 2050 to have a reasonable chance of limiting warming to 2ºC.[8]

A strong U.S. commitment to reduce emissions is essential to drive international climate progress. Voluntary initiatives to date have proven insufficient.  We urge U.S. policy makers to put our nation onto a path today to reduce emissions on the order of 80 percent below 2000 levels by 2050. The first step on this path should be reductions on the order of 15-20 percent below 2000 levels by 2020, which is achievable and consistent with sound economic policy. [5,6]

There is no time to waste. The most risky thing we can do is nothing.

 


1 Parry, M.L., O.F. Canziani, J.P. Palutikof, and co-authors. 2007. Technical Summary. In: Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden, and C.E. Hanson, eds. Cambridge University Press, 23-78.  For impacts on North America see Field, C.B., L.D. Mortsch, M. Brklacich, D.L. Forbes, P. Kovacs, J.A. Patz, S.W. Running, and M.J. Scott. 2007. North America. In: Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden, and C.E. Hanson, eds. Cambridge University Press, 617-652.  For additional reasons for concern see section 5.2 of Intergovernmental Panel on Climate Change Fourth Assessment Report Climate Change 2007: Synthesis Report.

2 Solomon, S., D. Qin, M. Manning, R.B. Alley, T. Berntsen, N.L. Bindoff, Z. Chen, A. Chidthaisong, J.M. Gregory, G.C. Hegerl, M. Heimann, B. Hewitson, B.J. Hoskins, F. Joos, J. Jouzel, V. Kattsov, U. Lohmann, T. Matsuno, M. Molina, N. Nicholls, J. Overpeck, G. Raga, V. Ramaswamy, J. Ren, M. Rusticucci, R. Somerville, T.F. Stocker, P. Whetton, R.A. Wood, and D. Wratt. 2007. Technical Summary. 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. S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller, eds. Cambridge University Press.

3 Barnett, T.P. D.W. Pierce, H.G. Hidalgo, C. Bonfils, B.D. Santer, T Das, G. Bala, A.W. Wood, T. Nozawa, A.A. Mirin, D.R. Cayan, M.D. Dettinger. 2008. Human-Induced Changes in the Hydrology of the Western United States, Science, 10.1126/science.1152538

4 Frumhoff, P.C., J.J. McCarthy, J.M. Melillo, S.C. Moser, and D.J. Wuebbles. 2007. Confronting Climate Change in the U.S. Northeast: Science, Impacts, and Solutions. Synthesis report of the Northeast Climate Impacts Assessment (NECIA). Cambridge, MA: Union of Concerned Scientists.

5 Barker T., I. Bashmakov, L. Bernstein, J.E. Bogner, P.R. Bosch, R. Dave, O.R. Davidson, B.S. Fisher, S. Gupta, K. Halsnæs, G.J. Heij, S. Kahn Ribeiro, S. Kobayashi, M.D. Levine, D.L. Martino, O. Masera, B. Metz, L.A. Meyer, G.-J. Nabuurs, A. Najam, N. Nakicenovic, H.-H. Rogner, J. Roy, J. Sathaye, R. Schock, P. Shukla, R.E.H. Sims, P. Smith, D.A. Tirpak, D. Urge-Vorsatz, and D. Zhou. 2007. Technical Summary. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer, eds. Cambridge University Press.  

6 Creyts, J., A. Derkach, S. Nyquist, K. Ostrowski, and J Stephenson. 2007. Reducing U.S. Greenhouse Gas Emissions: How Much at What Cost? McKinsey & Company. And Stern, N. 2007. The Economics of Climate Change: The Stern Review. Cambridge University Press.

7. Declaration of the leaders: The major economies forum on energy and climate. Presented at the G8 Summit, L'Aquila, Italy,
July 9, 2009. Online at http://www.g8italia2009.it/static/G8_Allegato/MEF_Declarationl.pdf.

8. Luers, A.L., M.D. Mastrandrea, K. Hayhoe, and P.C. Frumhoff. 2007. How to Avoid Dangerous Climate Change: A Target for U.S. Emissions Reductions. Cambridge, MA: Union of Concerned Scientists (www.ucsusa.org/global_warming/science/emissionstarget.html). This report assesses the U.S. contribution needed to stabilize atmospheric concentrations of greenhouse gases at a level <450 CO2 equivalent (CO2eq, the concentration of all greenhouse gases expressed in terms of CO2), under conservative assumptions.  These include developing nations' average annual emissions peak between 2020 and 2025 —10 to 15 years after those of industrialized nations.   Developing nations follow the Energy Information Agency (EIA) "low-growth" emissions trajectory up to their peak followed by average annual reductions rates that match those of industrialized nations.  Report assumptions also include allowing atmospheric concentrations to briefly go above (i.e. "overshoot") the target before returning to it by the end of the century. Stabilizing atmospheric concentrations at 450 ppm CO2eq provides a roughly 50-50 chance of limiting global average temperatures from rising more than 2°C above pre-industrial temperatures (M. Meinshausen, W.L. Hare, T.M.L. Wigley, D.P. van Vuuren, M.G.J. den Elzen, and R. Swart. 2006. Multi-gas emission pathways to meet climate targets. Climatic Change 75: 151-194). Literature estimates for global emissions reductions required to achieve a specific temperature or stabilized atmospheric concentration goal may vary as a result of whether or not concentrations are allowed to overshoot and return to the stabilization target and to representation of results in terms of different reference base years (e.g., 1990, 2000, 2005). See footnote 2 above with references therein and the 2007 Bali Climate Declaration by Scientists (online at http://www.climate.unsw.edu.au/bali; accessed December 2007). 

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