1 “Our Great Geophysical Experiment” Source: NOAA, Hurricane Katrina shortly before landfall

2 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.

3 Emissions: fossil fuel use generates CO2 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, …) The emissions -climate- impacts- policy nexus

4 2,000 1,600 1, CO2 emissions US (millions tC/yr)

5 Trend in CO2 emissions relative to GDP, US

66 Historical CO 2 concentrations at Mauna Loa Source:

77 Instrumental record: global mean temperature index(°C) Source: GISS, Hadley center.

8 Fossil (C) fuel + O 2 → Energy + CO 2 CO 2 has long atmospheric residence time as gas. CO 2 is a “greenhouse” gas that retains surface heat. The Greenhouse Effect: A CO 2 Blanket

9 Short wave radiation Long wave radiation

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: W/m 2 albedo: W/m 2 lapse rate: W/m 2 clouds: W/m 2 [Note: these standard conversion is.86 °C per W/m 2 ] 14

From CO 2 15

16 Projections and the paleoclimatic record

All GHGs,

18 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

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

21 Critical Scientific Developments Global data on economic and geophysical systems (1970s -) Computer speed of 50 %p. y. ( ) Computer software and high-level languages to implement mathematical programming algorithms (LP from 1960s, GAMS from 1980s) Conceptual modeling in all areas (1970s -) Internet and to improve access to researchers, data, and research around the world ( )

Basic mathematics of GCMs Physical math. Basic system is an elaboration of the basic equation above: 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: These are very nasty to solve for large systems. 22

The climate model schema 23

Estimates of Climate Sensitivity 24 Transient: After 70 years of 1% per year growth in CO2 concentrations. Equilibrium: Asymptotic change in global mean temperature.

25 Some projections of climate change with no policy A, B are IPCC scenarios; EMF and RICE are economic models

Long-run: CO2 assumption. Surface warming Thermal expansion of oceans Overturning of North Atlantic circulation. 26

27 Climate model projections with CO2 and other GHG Source: IPCC, Science

Warming by latitude 28

29 (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

Climate change: model average, northern winter 30

Climate change: model average, northern summer 31