Hansen et al 2006 Global Temperature Changes

Such feedbacks enhance the dichotomy between as and

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Unformatted text preview: cks such as GHG release, as well as sea level rise, will be limited if global temperature stays within the range of recent interglacial periods. Ice core data reveal a positive GHG feedback, GHG changes lagging temperature change, but the feedback magnitude is moderate (CO2, 20 ppm per °C; CH4, 50 ppb per °C) even if the entire observed gas change is a feedback (44). However, paleo data do not constrain the magnitude of feedbacks under BAU warming, which is far outside the range of interglacial temperatures. Such feedbacks enhance the dichotomy between AS and BAU scenarios. If global warming is not limited to 1°C, feedbacks may add to BAU emissions, making a ‘‘different planet’’ (17), including eventual ice-free Arctic, almost inevitable. The AS requires concerted efforts to both slow CO2 emissions and reduce atmospheric amounts of CH4, O3, and BC (17, 34). Achievement of the AS should limit positive climate feedbacks. However, continuation of BAU growth of CO2 emissions ( 2% per year) through 2015 yields 35% CO2 emissions relative to 2000 CO2 emissions and 40% CO2 emissions relative to AS 2015 CO2 emissions. Given the long life of CO2 and the impact of feedbacks on the plausibility of CH4 reductions, another decade of BAU emissions probably makes the AS infeasible. Inference of imminent dangerous climate change may stimulate discussion of ‘‘engineering fixes’’ to reduce global warming (45, 46). The notion of such a ‘‘fix’’ is itself dangerous if it diminishes efforts to reduce CO2 emissions, yet it also would be irresponsible not to consider all ways to minimize climate change. Considering the evidence that aerosol effects on clouds cause a large negative forcing (10), we suggest that seeding of clouds by ships plying selected ocean regions deserves investigation. However, given that a large portion of human-made CO2 will remain in the air for many centuries, sensible policies must focus on devising energy strategies that greatly reduce CO2 emissions. 1. Hansen J, Sato M, Ruedy R, Nazarenko L, Lacis A, Schmidt GA, Russell G, Aleinov I, Bauer M, Bell N, et al. (September 28, 2005) J Geophys Res 110:10.1029 2005JD005776. 2. Pierrehumbert RT (2000) Proc Natl Acad Sci USA 97:1355–1358. 3. Lea DW (2004) J Climate 17:2170–2179. 4. Hansen J, Ruedy R, Sato M, Imhoff M, Lawrence W, Easterling D, Peterson T, Karl T (2001) J Geophys Res 106:23947–23963. 5. Reynolds RW, Smith TM (1994) J Clim 7:929–948. 6. Rayner N, Parker D, Horton E, Folland C, Alexander L, Rowell D, Kent E, Kaplan, A (July 17, 2003) J Geophys Res 108:10.1029 2002JD002670. 7. Hansen J, Lebedeff S (1987) J Geophys Res 92:13345–13372. 8. Hansen J, Ruedy R, Glascoe J, Sato M (1999) J Geophys Res 104:30997–31022. 9. Comiso JC (2006) Weather 61:70–76. 10. Intergovernmental Panel on Climate Change (2001) Climate Change 2001: The Scientific Basis, eds. Houghton JT, Ding Y, Griggs DJ, Noguer M, van der Linden PJ, Dai X, Maskell K, Johnson CA (Cambridge Univ Press, Cambridge, UK). 11. Manabe S, Wetherald RT (1975) J Atmos Sci 32:3–15...
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This document was uploaded on 03/15/2014 for the course MEA 570 at N.C. State.

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