“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
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