“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

The emissions -climate impacts policy nexus

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, …) 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 CO 2 concentrations at Mauna Loa

390 380 370 360 350 340 330 320 310 60 65 70 75 80 85 90 95 00 05 Source: http://www.mlo.noaa.gov/home.html

Instrumental record: global mean temperature index(°C)

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

-0.4

1850 GISS Hadley US NCDC 1875 1900 1925 1950 1975 2000 Source: GISS, Hadley center.

The Greenhouse Effect:

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.

A CO 2 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: albedo: lapse rate: clouds: 1.8 + .18 W/m 2 0.26 + 0.08 W/m 2 -0.84 + 0.26 W/m 2 0.69 + 0.38 W/m 2 [Note: these standard conversion is .86 °C per W/m 2 ] 14

From CO 2

15

Projections and the paleoclimatic record

Temperature record and projections to 2200, Vostok core, Antarctica 8 -4 -8 4 0 -12 -400,000 -300,000 -200,000 Years before present -100,000 0 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) =



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 the point.

α

are parameters reflect aggregation and imperfect understanding. N(i,j,k) refers to cells in the neighborhood of 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 2 1 4 3 Transient Equilibrium 0 0 1 2 3 4 Temperature increase for CO2 doubling (°C) 5 6 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

1.5

1.0

0.5

0.0

5.0

4.5

4.0

3.5

3.0

2.5

2.0

A2 B1 B2 RICE-201 EMF-22 A1B 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

.28

.24

.20

.16

.12

.08

.04

.00

-80

Warming by latitude

Share population T: Hadley T: GISS T: NCAR T: GFDL -40 0 Latitude 40 4 2 80 0 14 8 6 12 10 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