MIT OpenCourseWare http://ocw.mit.edu 15.023J / 12.848J / ESD.128J Global Climate Change: Economics, Science, and PolicySpring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.15.023-12.848-12.308-ESD.128GLOBAL CLIMATE CHANGE: ECONOMICS, SCIENCE AND POLICYR. PRINN, FEBRUARY 19, 2008THE CLIMATE MACHINE IPast Climate, and Gases, Aerosols and Radiation1. Past Climate Trends2. The Climate System3. Energy Balance in the Climate System4. Radiative Forcing of Climate5. Carbon Dioxide and the Carbon Cycle6. Other Greenhouse Gases & AerosolsFrom: Petit et al., NATURE, 399: 429-436 (1999)⇑⇑⇑HOW HAVE TEMPERATURE & GREENHOUSE GASES CHANGED OVER THE PAST 400,000 YEARS?HOW HAS TEMPERATURE CHANGED OVER THE PAST 1200 YEARS?Figure and text removed due to copyright restrictions. See figure entitled “Records of past climate” in:Briffa, Keith, and Timothy Osborn. “Blowing Hot and Cold.” Science 295 (2002): 2227-2228.Ref: IPCC 4th Assessment, Summary for Policymakers, Feb. 2, 2007HOW HAVE GLOBAL TEMPERATURE & SEA LEVEL, & N.H.SNOW COVER CHANGED OVER THE PAST 150 YEARS?1998 and 2005 had the highest temperatures ever recordedSea level rise driven by expanding ocean water and melting glaciersLess snow cover means more sunlight absorbed & increased warmingCourtesy of the Intergovernmental Panel on Climate Change. Used with permission. From: Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Figure SPM.3, Cambridge University Press.HOW HAVE CONTINENTAL TEMPERATURES CHANGEDOVER THE PAST CENTURY (1906-2005), AND WHY?Black lines:observed changes. Blue bands: range for 19 model simulations using natural forcings.Red bands: range for 51 model simulations using natural and human forcings.Ref: IPCC 4th Assessment, Summary for Policymakers, Feb. 2, 2007Courtesy of the Intergovernmental Panel on Climate Change. Used with permission.IMAGESFromNASA’sTERRAsatelliteInvestigation of this complex systemrequires an integrated approachWHAT IS THE NATURE OF THE SYSTEM THAT DETERMINES CLIMATE?WHAT IS THE NATURE OF THE SYSTEM THAT DETERMINES CLIMATE?WHAT COULDFORCECLIMATE CHANGE?CLIMATESYSTEM COMPONENTSCourtesy of the Intergovernmental Panel on Climate Change. Used with permission.WHAT ARE THE VERTICAL FLOWS OF ENERGYTHAT DETERMINE GLOBAL TEMPERATURES?THE FUNDAMENTAL UNITS WE WILL USETO MEASURE FLOWS ARE WATTS/(METER)2ENERGY BALANCE IN THE CLIMATE SYSTEMENERGY BALANCE IN THE CLIMATE SYSTEMESSENCEOF THE GREEN-HOUSEEFFECTCourtesy of the Intergovernmental Panel on Climate Change. Used with permission.HOW HAVE THE ENERGY FLOWSCHANGED SINCE PRE-INDUSTRIAL TIMES?RADIATIVE FORCING (watt/m2) IS THE CHANGE IN THE VERTICAL ENERGY FLOW (at the tropopause) INDUCED BY CHANGESIN GREENHOUSE GASES, AEROSOLS, & OTHER CLIMATE FORCING PROCESSESHUMAN & OTHER INFLUENCES ON CLIMATEHOW IS THE COMPOSITION OF THE ATMOSPHERE CHANGING?Ref: IPCC 4th Assessment, Summary for Policymakers, Feb. 2, 2007ATMOSPHERIC COMPOSITION & RADIATIVE FORCING: TRENDS OVER THE LAST 20,000 YEARS The concentrations and radiative forcing by (a) carbon dioxide (CO2), (b) methane (CH4), (c) nitrous oxide (N2O) and (d) the rate of change in their combined radiative forcing over the last 20,000 years reconstructed from Antarctic and Greenland ice and firn data (symbols) and direct atmospheric measurements (panels a,b,c, red lines). The grey bars show the reconstructed ranges of natural variability for the past 650,000 years. The rate of change in radiative forcing (panel d, black line) has been computed from spline fits to the concentration data. The negative rate of change in forcing around 1600 shown in the higher-resolution inset in panel d results from a CO2decrease of about 10 ppmin the ice core record.Courtesy of the Intergovernmental Panel on Climate Change. Used with permission.WHAT CONTROLS GREENHOUSE GAS AND AEROSOL LEVELS?Courtesy of the Intergovernmental Panel on Climate Change. Used with permission.WATER VAPOR IS THE MOST POWERFUL GREEN-HOUSE GAS!WHAT ARE THE EFFECTS OFAEROSOLS ON CLIMATE? Direct Effect: aerosols reflect or absorb sunlight leading to warming or coolingIndirect Effects: aerosols create more and smaller cloud droplets which: (1) increases reflection, and(2) suppresses rainfallSemi-direct effects: absorbing aerosolsheat air and cool surface suppressingconvection and condensationDO WE HAVE EVIDENCE FOR GLOBAL COOLING BY SULFATE AEROSOLS?⇑⇑⇑Hansen, J., R. Ruedy, M. Sato, R. Reynolds, "Global Surface Air Temperature in 1995: Return to Pre-Pinatubo Level." Geophys Res Lett 23, no. 13 (1665-1668, 1996). Copyright [1996] American Geophysical Union. Reproduced/modified by permission of American Geophysical Union.WHAT ARE THE MAJOR HUMAN & NATURAL ACTIVITIES FORCING CLIMATE CHANGE IN THE INDUSTRIAL ERA (1750-2005)?Ref: adapted from IPCC 4th Assessment, Summary for Policymakers, Feb. 2,