1 Online Course Evaluations SIO course and instructor online evaluations are open November 22 - December 5, 2010 for Fall Quarter 2010. Please announce the link to the students: https://sio.ucsd.edu/secure/student/course_eval/ The students received an email message and will receive reminder email messages on how to access the evaluations. The students must complete the evaluations from November 22 - December 5, 2010. !Presentation Schedule Monday 80 min • Johannes – 10+2 • Scutrhabit (Bryan, Chi, Patrick) – 30+6 • Kristin+Amelia? – 20+2 Wednesday • Thunderclap (Michelle, James, Matt) – 30+6 • Dan – 10+2 • Nick? – 10+2 Review Session • Friday 12/3 – 3pm – Final Exam: Thursday 12/9 at 11:30 am here Climate Feedbacks - A Study Guide to Chapter 13 This topic is extremely important and is central to modern research on climate, especially anthropogenic climate change. It is no exaggeration to say that understanding feedbacks in the climate system is a major challenge to science, and indeed to humanity. However, the Chapter 13 formalism (from control theory) can obscure rather than illuminate key issues. “Perturbation/Forcing” e.g. double CO2 Feedback e.g. water vapor increases Overall Effect The Enhanced Greenhouse Effect Solar (S) and longwave (L) radiation in Wm-2 at the top of the atmosphere S L 236 236 T = -18°C S L 236 232 CO2 x 2 S L 236 236 CO2 x 2 S L 236 236 CO2 x 2 + Feedbacks H2O (+60%) Ice/Albedo (+20%) Cloud? Ocean? TS = 15°C TS = 15°C ΔTS ~ 1.2K ΔTS ~ 2.5K2 The chapter emphasizes 3 especially important feedbacks (but there are many others). Section 13.3 Water Vapor Feedback Section 13.4 Cloud-radiation Feedback Section 13.5 Snow/Ice-albedo Feedback One complexity is that these feedbacks (and others) can and do interact with one another. The partial derivatives in the control theory formalism are an idealization that cannot be observed in the “real world” -- rarely does only one variable vary. Feedbacks also often involve the following complexities: The climate system is not linear. Important “tipping points” or thresholds or instabilities are known to exist. The base state can influence the feedbacks. Example: Snow-albedo feedback depends on snow being present. A global average can be misleading. Feedbacks may be locally important but less important in the global mean. Climate sensitivity depends strongly on feedbacks, and the usual way of defining it, as a surface temperature change in response to doubling CO2, is not always best. Sea level rise The Development of Climate models, Past, Present and Future Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere Land surface Land surface Land surface Land surface Land surface Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice Sulphate aerosol Sulphate aerosol Sulphate aerosol Non-sulphate aerosol Non-sulphate aerosol Carbon cycle Carbon cycle Atmospheric chemistry Ocean & sea-ice model Sulphur cycle model Non-sulphate aerosols Carbon cycle model Land carbon cycle model Ocean carbon cycle model Atmospheric chemistry Atmospheric chemistry Off-line model development Strengthening colours denote improvements in models Mid 1970s Mid 1980s Early 1990s Late 1990s Present day Early 2000s? Section 13.3 Water Vapor Feedback Key points: This is a strongly positive feedback, nearly doubling the effect of carbon dioxide alone. Relative humidity seems to be approximately constant under climate change (p. 359). Relatively dry regions, such as the upper troposphere and polar regions, are especially sensitive (p. 362).3 Water Vapor Feedback Loop Increase CO2 Increase Temperature Increase Water Vapor Water Vapor Feedback Approximately Doubles the Sensitivity of Climate ~1 to 2 ˚C warming +3C ~ +20% H2O Natural Feedbacks within the Climate System:Water Vapor Feedback Change in Global Water Vapor at 2xCO2 All models predict total column water vapor to increase at 7% /K!Change in Upper Tropospheric Water Vapor at 2xCO2 All models predict upper trop water vapor to increase at ~15% /K!Section 13.4 Cloud-radiation Feedback Key points: Clouds affect both shortwave (low clouds) and longwave (high clouds). Present climate has cloud cooling dominating cloud warming (pp. 368-369). Many different mechanisms, including those involving aerosol-cloud interactions, may be important, but the sign and magnitude of cloud feedbacks is still largely unknown (p. 374). Clouds have big effects in models.4 Model Estimates of Cloud Radiative Forcing with CO2 Doubling Effect of cloud feedback formulation on climate prediction • Feedback scheme Global Av Temp change,C for doubled CO2 – RH 5.3 – CW 2.8 – CWRP 1.9 – after Senior & Mitchell, Hadley Centre Senior, C. A., and J. F. B. Mitchell, 1993: Carbon Dioxide and Climate: The Impact of Cloud Parameterization. Journal of Climate, 6, 393-418. This classic paper showed that the same climate model can produce different sensitivites to carbon dioxide, varying by a factor of three in terms of global average warming, depending on the treatment of clouds and cloud-radiation interactions. Evolution of Climate Sensitivity in AM2 0123452xCO2 Sensitivity (K)4.53.94.34.62.62.9p5p7p9p10p12ap12bNew BL Scheme Global Mean ΔTs (K) 4.5 1.5 Large change in sensitivity occurred between AM2p10 and AM2p12a due to the introduction of a new boundary layer parameterization, which modifies the response of low-level clouds to warming Section 13.5 Snow/Ice-albedo Feedback Key points: This feedback is large and positive in high northern latitudes. Observations show that this effect is occurring now. Melting ice on land has another large effect, unrelated to albedo: it causes sea level to
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