Transcript Impacts_week10_post

Agenda for today
1.
2.
3.
4.
Global warming and extreme events
Summary of damages
The 2 °C target
Non-linearities, tipping points, and decisions
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Estimates of Impacts on Agriculture late in the 21st C
Impacts on net value of agriculture as percent of national or
global income:
Mendelsohn
Cline
North American
+ 0.4 %
+ 0.5 %
Africa
- 5.0 %
- 4.0 %
Global average
- 0.2 %
- 0.1 to -.05%
Estimated effect of ag on output is small because (1)
agriculture is small, (2) farmers can adapt, (3) CO2 is a
fertilizer.
Query: Assume this is for 2075 for constant share of ag. What if
share declines by half?
Source: Mendelsohn et al.; Cline
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The tricky issue of declining share of agriculture
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High income
East Asia
Latin America
South Asia
Sub-Saharan Africa
Share of agriculture in GDP (%)
40
35
30
25
20
15
10
5
0
1965
1970
1975
1980
1985
1990
1995
2000
2005
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Price of carbon emissions
The basic analytical structure
Marginal Damages
Marginal Cost
Pcarbon*
0
Market!
Abatement*
Abatement
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Where does the marginal damage function come from?
1. Consider output as function of climate:
Qt = f(Kt , Lt , At ; Tt )
This would be appropriate sum over sectors, individuals, countries,
and time periods.
2. Then get the damage function as function of T relative to base T:
Dt = f(Kt , Lt , At ; Tt ) - f(Kt , Lt , At ; T0 )
3. We then relate temperature to past emissions:
Tt = g( E0 , E1 , E2 , … , Et )
4. From which we get the marginal damage function. Here, the
marginal damage (sometimes called social cost of carbon) is:

SCC t = MD t = [PV (D t )] / E t = [

v=t
D ve
rv
] / E t
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First Generation Estimates of Aggregate
Monetized Damages of CO2 Doubling, U.S., for
present economy
Source: IPCC, Second Assessment Report
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Damage summary from Tol survey: global
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Damages as percent of output
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Dots
from
Tol survey
4
IPCC
estimate
3
2
1
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
-1
-2
-3
Global mean temperature increase (°C)
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Damage summary: global
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Dots
from
Tol survey
Damages as percent of output
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4
Line is Yale
DICE/RICE
model
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2
1
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
-1
-2
-3
Global mean temperature increase (°C)
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Targets for international policy
• Framework for international climate change policy is
United Nations Framework Convention on Climate
Change, ratified in 1994
• This stated target as “The ultimate objective … is to
achieve … stabilization of greenhouse gas concentrations
in the atmosphere at a level that would prevent
dangerous anthropogenic interference with the climate
system.”
• No consensus on what is meaning of “dangerous
anthropogenic interference “
.
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The 2 °C target
• Current policy has focused on a target of 2 °C rise from
pre-industrial times.
• Copenhagen Accord of December 2009, which
“recognized … the scientific view that the increase in
global temperature should be below 2 degrees Celsius.”
• Sources of “scientific view”:
– Climate history over long run
– Possible tipping points in climate system
– Thresholds for ecosystems
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German Advisory Council on Global Change (1995)
• In order to arrive at an approximate but sound assessment of the possible
impacts of climate change…, the Council applies the principles of
preservation of Creation [and] prevention of excessive costs.
• The first principle, preservation of Creation in its present form, is presented
within this scenario in the form of a tolerable “temperature window”. This
window is derived from the range of fluctuation for the Earth’s mean
temperature in the late Quarternary period.
• This geological epoch has shaped our present-day environment, with the
lowest temperatures occurring in the last ice age (mean minimum around
10.4 °C) and the highest temperatures during the last interglacial period
(mean maximum around 16.1 °C). If this temperature range is exceeded in
either direction, dramatic changes in the composition and function of
today’s ecosystems can be expected.
• If we extend the tolerance range by a further 0.5 °C at either end, then the
tolerable temperature window extends from 9.9 °C to 16.6 °C. Today’s
global mean temperature is around 15.3 °C, which means that the
temperature span to the tolerable maximum is currently only 1.3 °C.
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Long-term climate history
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Non-linearities in the climate system
Most of the impacts literature examines gradual climate change,
with roughly linear systems and impacts.
Scientists have been particularly concerned about
discontinuities, abrupt climate change, tipping points,
catastrophic impacts.
From economic/decision point of view, thresholds can simplify
decisions as to the optimal policy.
… EXTREMELY SEDUCTIVE FOR POLICYMAKERS!
Optimum Without Thresholds
Marginal
Abatement
Cost
0
Marginal Damage
Temperature*
Temperature
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Optimum With Single Thresholds
Marginal Damage
Marginal
Abatement
Cost
0
Temperature*
Temperature
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Tipping Elements in the Climate System
“Tipping elements in the Earth’s climate system, “ T. M. Lenton, et al.,
PNAS, Feb 2008.
Simulation of Melting
IPCC, Science, AR4, p. 830 from Ridley. This is roughly for a 6 °C
warming. Note that some climatologists think that this underestimates
the rate of melting.
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Hysteresis loops and Tipping Points for Ice Sheets
Frank Pattyn, “GRANTISM: Model of Greenland and Antrarctica,” Computers
& Geosciences, April 2006, Pages 316-325
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Multiple Thresholds
Total
Damage
0
Temperature*
Temperature
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Optimum With Thresholds???
Marginal
Abatement
Cost
0
Marginal Damage
Temperature*
Temperature
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Optimum With Multiple Thresholds
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Abatement
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Damages
8
6
4
2
0
0
1
2
3
4
5
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Optimum With Multiple Thresholds:
Cannot Use Simple Marginal Analysis!
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10
8
6
Abatement
Damages
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Sum
2
0
0
1
2
3
4
5
6
Overall Assessment
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Summary of Impacts Estimates
Early studies contained a major surprise:
Modest impacts for gradual climate change, market impacts, highincome economies, next 50-100 years:
- Impact about 0 (+ 2) percent of output.
- Further studies confirmed this general result.
BUT, outside of this narrow finding, potential for big problems:
- many subtle thresholds and tipping elements
- abrupt climate change (“inevitable surprises”)
- many ecological disruptions (ocean carbonization, species loss, forest
wildfires, loss of terrestrial glaciers, snow packs, …)
- stress to small, topical, developing countries
- gradual coastal inundation of 1 – 10 meters over 1-5 centuries
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Why Impact Analysis is So Difficult
1. Most impacts analyses impose climate changes on current socialeconomic-political structures.
- Example: impact of temp/precip/CO2 on structure of Indian economy in
2005
2. However, need to consider what society will look like when climate
change occurs.
3. Example of difficulties of looking backward:
–
2 ˚C increase in 6-7 decades – that was Nazism, period of Great
Depression, Gold Standard, pre-Keynesian macro
–
4 ˚C increase in 15 decades –Ming Dynasty, lighting with
whale oil, invention of telegraph, stagecoach, ….
4. In the end, it appears that major impacts are NON-MARKET, VERY
DIFFICULT TO VALUE, and VERY CONTENTIOUS.
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