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Unformatted text preview: IOP P UBLISHING E NVIRONMENTAL RESEARCH LETTERS Environ. Res. Lett. 3 (2008) 044002 (6pp) doi:10.1088/1748-9326/3/4/044002 What do recent advances in quantifying climate and carbon cycle uncertainties mean for climate policy? Joanna I House 1 , 5 , Chris Huntingford 2 , Wolfgang Knorr 1 , Sarah E Cornell 1 , Peter M Cox 3 , Glen R Harris 4 , Chris D Jones 4 , Jason A Lowe 4 and I Colin Prentice 1 1 QUEST, Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK 2 CEH Wallingford, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK 3 School of Engineering, Computer Science and Mathematics, University of Exeter, Harrison Building, North Park Road, Exeter EX4 4QF, UK 4 Hadley Centre for Climate Prediction and Research, Met Office, FitzRoy Road, Exeter, Devon EX1 3PB, UK E-mail: [email protected] Received 4 June 2008 Accepted for publication 10 September 2008 Published 14 October 2008 Online at stacks.iop.org/ERL/3/044002 Abstract Global policy targets for greenhouse gas emissions reductions are being negotiated. The amount of emitted carbon dioxide remaining in the atmosphere is controlled by carbon cycle processes in the ocean and on land. These processes are themselves affected by climate. The resulting ‘climate–carbon cycle feedback’ has recently been quantified, but the policy implications have not. Using a scheme to emulate the range of state-of-the-art model results for climate feedback strength, including the modelled range of climate sensitivity and other key uncertainties, we analyse recent global targets. The G8 target of a 50% cut in emissions by 2050 leaves CO 2 concentrations rising rapidly, approaching 1000 ppm by 2300. The Stern Review’s proposed 25% cut in emissions by 2050, continuing to an 80% cut, does in fact approach stabilization of CO 2 concentration on a policy-relevant (century) timescale, with most models projecting concentrations between 500 and 600 ppm by 2100. However concentrations continue to rise gradually. Long-term stabilization at 550 ppm CO 2 requires cuts in emissions of 81 to 90% by 2300, and more beyond as a portion of the CO 2 emitted persists for centuries to millennia. Reductions of other greenhouse gases cannot compensate for the long-term effects of emitting CO 2 . Keywords: carbon dioxide, climate, policy, carbon cycle, feedbacks, uncertainty, Stern Review, emissions targets, stabilisation 1. Introduction: climate policy The temperature increase due to human activity since pre- industrial times has been in the order of 0 . 8 ◦ C (IPCC 2007 ). The Intergovernmental Panel on Climate Change 5 Author to whom any correspondence should be addressed. ( 2007 ) projected an additional global warming of 1.1–6 . 4 ◦ C for the 21st century based on greenhouse gas emissions scenarios (SRES) that intentionally exclude mitigation policy (Naki´cenovi´c and Swart 2000 ). The United Nations Framework Convention on Climate Change commits its signatories to achieve ‘...
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This note was uploaded on 08/23/2011 for the course ECE 4833 taught by Professor Doolittle during the Spring '10 term at Georgia Tech.
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