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“Our Great Geophysical Experiment” 1 The basic outline for the rest of the course 1. The science of global warming. 2. The impacts of global warming on markets and environmental systems. 3. Why global warming poses such difficult problems for economic and environmental policy and the theory of stock global public goods. 4. The use of integrated assessment models to analyze trends and examine policies. 5. Alternative strategies for slowing climate change, especially cap and trade, the Kyoto Protocol, and carbon taxes. 2 Emissions: fossil fuel use generates CO2 The emissions -climateimpactspolicy nexus Carbon cycle: redistributes C around atmosphere, oceans, etc. Climate system: change in radiation warming, precip., ocean currents, etc.. Impacts on ecosystems, agriculture, diseases, skiing, golfing, … Policies: Measures to control emissions (limits, taxes, subsidies, …) 3 CO2 emissions US (millions tC/yr) 2,000 1,600 1,200 800 400 1930 1940 1950 1960 1970 1980 1990 2000 2010 4 Trend in CO2 emissions relative to GDP, US .6 .5 .4 .3 .2 CO2-GDP ratio Trend (-1.7 percent per year) .1 1930 1940 1950 1960 1970 1980 1990 2000 2010 5 Historical CO2 concentrations at Mauna Loa 390 380 370 360 350 340 330 320 310 60 65 70 75 80 85 90 Source: http://www.mlo.noaa.gov/home.html 95 00 05 6 Instrumental record: global mean temperature index(°C) Temperature anomaly (1895-1905 = 0) 1.0 0.8 GISS Hadley US NCDC 0.6 0.4 0.2 0.0 -0.2 -0.4 1850 1875 1900 Source: GISS, Hadley center. 1925 1950 1975 2000 7 The Greenhouse Effect: Fossil (C) fuel + O2 → Energy + CO2 CO2 has long atmospheric residence time as gas. CO2 is a “greenhouse” gas that retains surface heat. A CO2 Blanket 8 Short wave radiation Long wave radiation 9 Energy balance of the earth 10 Radiative forcing and climate change 11 Absorption on the spectrum 12 Central notion of radiative forcings “The radiative forcing of the surface-troposphere system due to the perturbation (say, a change in greenhouse gas concentrations) is the change in net (down minus up) irradiance (solar plus long-wave in Wm-2) at the tropopause AFTER allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values.” IPCC Basic equation: ΔT = λ ΔF where T = mean surface temperature, F = forcings (W/m2), and λ is a feedback parameter. 13 Model uncertainty of the 20 models surveyed With CO2 doubling: Direct forcing effect: 1.2 °C per CO2 doubling Indirect effects: water vapor: 1.8 + .18 W/m2 albedo: 0.26 + 0.08 W/m2 lapse rate: -0.84 + 0.26 W/m2 clouds: 0.69 + 0.38 W/m2 [Note: these standard conversion is .86 °C per W/m2] 14 From CO2 15 Projections and the paleoclimatic record Temperature record and projections to 2200, Vostok core, Antarctica Temperature (2000 = 0) 8 4 0 -4 -8 -12 -400,000 -300,000 -200,000 -100,000 0 Years before present 16 All GHGs, 2005 17 Atmospheric Ocean General Circulation Models - - These are the workhorses of climate change science. They are 3D computerized time-stepped simulation models of the atmosphere, oceans, cryosphere, and biosphere Based on fundamental physics (conservation, etc.), geography (where are oceans), and observations (initial conditions) Used to predict weather first, now climate, both historically and in the future Large ones are still very coarse grid (100 x 100 km) and require supercomputers (e.g., 8 TFLOP for GFDL). Because of complex physics, large remaining errors in and across GCMs 18 Model development over the last decades AR4, Chapter 1. 19 Geographic resolution characteristic of the generations of climate models used in the IPCC Assessment Reports: FAR (IPCC, 1990) and AR4 (2007). (Source: IPCC, AR4) 20 Basic mathematics of GCMs Physical math. Basic system is an elaboration of the basic equation above: x(i, j, k; t) = f [x(i , j , k ; t - 1); ] N(i, j,k) For locations (i, j, k) and small time steps, subject to initial conditions, complex geography, laws of physics and chemistry, many parameterizations to The α are parameters reflect aggregation and imperfect understanding. N(i,j,k) refers to cells in the neighborhood of the point. Note that this is a recursive system. Relatively simple to solve. Economic systems are often much more complex to solve because they involve forward-looking elements: p(i,t) = f [x(i ,t), p(i,t - 1), p(i,t + 1)] These are very nasty to solve for large systems. 22 The climate model schema 23 Estimates of Climate Sensitivity Averages of models are at arrows: 5 Number of models Transient Equilibrium 4 3 2 1 0 0 1 2 3 4 5 6 Temperature increase for CO2 doubling (°C) Transient: After 70 years of 1% per year growth in CO2 concentrations. Equilibrium: Asymptotic change in global mean temperature. 24 Some projections of climate change with no policy 5.0 4.5 RICE-201 EMF-22 Global mean temperature increase (from 1900, ◦C) 4.0 A1B 3.5 A2 3.0 B1 2.5 B2 2.0 1.5 1.0 0.5 0.0 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 A, B are IPCC scenarios; EMF and RICE are economic models 25 Long-run: CO2 assumption. Surface warming Thermal expansion of oceans Overturning of North Atlantic circulation. 26 Climate model projections with CO2 and other GHG Climate model projections with CO2 and other GHG Source: IPCC, Science 27 Warming by latitude .28 14 Share population T: Hadley T: GISS T: NCAR T: GFDL .20 12 10 .16 8 .12 6 .08 4 .04 2 .00 0 -80 -40 0 Latitude 40 80 Temperature change (oC) Share global population .24 28 (a) Atmospheric CO2 emissions and changes in ocean pH and (b) projections compared with history(A and C), uncontrolled C/W (D); red + = uncontrolled WN; green triangle = “optimal” WN) Caldeira and Wickett, Nature 2003 29 Climate change: model average, northern winter 30 Climate change: model average, northern summer 31