After Durban:After Durban:What is the Politically Sustainable PathWhat is the Politically Sustainable Path
of Targets for Greenhouse Gas Emissions?of Targets for Greenhouse Gas Emissions?
Jeffrey FrankelJeffrey Frankel Harpel Professor, Harvard Kennedy School, March 27, 2012Harpel Professor, Harvard Kennedy School, March 27, 2012
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The QuestionThe Question1. At Durban (Dec. 2012), developing countries essentially agreed at last to join
the same GHG emissions control regime as industrialized countries:– A “non-binding agreement to reach an agreement” by 2015
bringing all countries under the same legal regime by 2020,– thus replacing the Berlin Mandate (1995).
2. But they still refuse to sacrifice their economic development -- as understandable as ever.
3. The question: how to set emission targets so as to take proper account of country differences, esp. income.
33
Sustainable cooperationSustainable cooperation::
Need to bridgeNeed to bridge
• the gap between rich countries & poor,
• the gap between environmental aspirations & economic costs that people are willing to pay,
• the gap between what leaders say, &what commitments are enforceable/credible.
44
There are grounds for hope that the Durban There are grounds for hope that the Durban climate regime will follow Kyoto, but fix itclimate regime will follow Kyoto, but fix it
• Features of the Kyoto Protocol worth building on --– Politics: Quantitative limits maximize national sovereignty– Economics: Market mechanisms, esp. international permit trading– Thus (2001) “You’re Getting Warmer: The Most Feasible Path
for Addressing Global Climate Change Does Run Through Kyoto.”
• What was sorely missing from Kyoto:– Participation by US, China, & other developing countries– A mechanism for setting targets further into the future, past 2012– Any reason to expect compliance.
55
ProgressProgress
• Most countries (>80) responded to the Copenhagen Accord in 2010 by submitting plans for reducing emissions.
• By the time of Cancun, 21 countries had associated themselves with specific quantitative targets
• counting the EU27 as one
• and including 7 big non-Annex-I countries.
• Of course some, like China or US, are vague • about seriousness of commitment.
• Also India & China’s 2020 target ≈ BAU (Business as Usual). • But that is not a problem. It is what we have proposed all along.
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• unlike other approaches based purely on:
– Science (concentration goals),
– Ethics (equal emission rights per capita),
– or Economics (cost-benefit optimization).
• Why the political approach? – Countries will not accept burdens they view as unfair.– Above certain thresholds for economic costs, they will drop out.
My Proposal: formulas for pragmatic targets, based on what emission paths are sustainable politically:
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““An Elaborated Proposal For Global Climate Policy An Elaborated Proposal For Global Climate Policy Architecture: Specific Formulas and Emission Architecture: Specific Formulas and Emission
Targets for All Countries in All Decades” (2009)Targets for All Countries in All Decades” (2009)
suggested a framework of formulas that produce precise numerical targets for CO2 emissions in all regions for the rest of the century,
subject to political constraints:subject to political constraints:
No country suffers loss (PDV) No country suffers loss (PDV) >> Y= Y=11% GDP% GDP, , by signing up ex ante,by signing up ex ante,
nor suffers a loss nor suffers a loss >> XX=5% GDP=5% GDP, , in any one period, by abiding ex post.in any one period, by abiding ex post.
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Maximizing the credibility of agreement,Maximizing the credibility of agreement,for any given environmental goalfor any given environmental goal
Aggressiveness of targeted cut in CO2 concentrations by 2100
Credibility ofan agreement,
Vs. probabilitythat it will un-ravel because(e.g.) some key players find that complying imposes huge economic costs, relative to dropping out.
•
••
Frankel (2009)Bosetti & F (UNDP, 2011)
Bosetti & Frankel (REEP)
Some proposals
500 ppm|
450 ppm|
350 ppm|
•
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• Stage 2:Stage 2: When the time comes for developing country cuts, When the time comes for developing country cuts, targets are determined by a formula incorporating targets are determined by a formula incorporating 3 elements, designed so each is asked only to take actions 3 elements, designed so each is asked only to take actions analogous to those already taken by others:analogous to those already taken by others:
– a Progressive Reduction Factor,– a Latecomer Catch-up Factor, and
– a Gradual Equalization Factor.
• Stage 1: • Advanced countries commit to the targets that their leaders have already announced for 2020.• Others commit immediately not to exceed BAU.
Proposal
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The three factors in the formulasThe three factors in the formulas
• Progressive Reduction Factor: – For each 1% difference in income/cap =>
target is γ % greater emissions abatement from BAU.
• Latecomer Catch-up Factor: – Gradually close the gap between the latecomer’s starting point
& its 1990 emission levels at λ per year. (Goal: avoid rewarding latecomers for ramping up emissions).
– Baseline perhaps now moved from 1990 to 2005.
• Gradual Equalization Factor: – In the long run, rich & poor countries’ targets converge
in emissions per capita at δ per year. (Goal: equity)
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Where do the parameters come from?Where do the parameters come from?
• They would be negotiated.
• But a good start is to use parameters implicit in targets that have already been agreed.
• The degree of progressivity in the PRF can be estimated from observed pattern– in allocations among countries already agreed (γ=.14).
• We estimated Latecomer Catch-up parameter from the speed with which US targets close the gap: current vs. 1990 emission levels– in Lieberman-Warner (2008) & Waxman-Markey bills (2009) => λ =.3 per 5-yr. period.
• Initially we set speed of Gradual Equalization δ=.1, per 5-yr. budget period (which comes to dominate per capita targets toward the end of the century).
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The targeted reductions from BAU agreed to at Kyoto The targeted reductions from BAU agreed to at Kyoto
in 1997 were progressive with respect to income.in 1997 were progressive with respect to income.
-30%
-20%
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0%
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50%
2.699 3.699 4.699
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s-as-
usu
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.
500 1,000 2,000 5,000 10,000 20,000 50,000
1996 GDP per capita (1987 US dollars, ratio scale)
Cuts ↑
Incomes →This is how we set the parameter in the Progressive Reductions Factor
γ =.14
1313
The resultant paths for emissions targets, The resultant paths for emissions targets, permit trading, the price of carbon, permit trading, the price of carbon, GDP costs, & environmental effectsGDP costs, & environmental effects
are estimated by means of the WITCH model of FEEM, Milan,
co-authored & applied by Valentina Bosetti.
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World Industrial Carbon Emissions
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bau
SimulatedEmissions
Global peak Global peak date ≈ 2035date ≈ 2035
◙ ◙ Constraints are satisfied:Constraints are satisfied: -- No country in any one period suffers -- No country in any one period suffers a loss as large as 5% of GDP by participating.a loss as large as 5% of GDP by participating. -- Present Discounted Value of loss < 1% GDP. -- Present Discounted Value of loss < 1% GDP.
◙ ◙ In 2009 version, CO2 concentrations level off In 2009 version, CO2 concentrations level off at 500 ppm in the latter part of the century.at 500 ppm in the latter part of the century.
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The last published paperThe last published paper ((REEPREEP) ) co-authored with Valentina Bosettico-authored with Valentina Bosetti
was an attempt to see if we could hit CO2 concentrations = 450 ppm– by assuming more aggressive parameters in the formulas.
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Latest Bosetti-Frankel study Latest Bosetti-Frankel study (2011)(2011)
• updates all the estimates• to reflect recent developments in
the economy, environment, & negotiations,– particularly the Copenhagen-Cancun country targets,– and to reflect new technologies, including
• Wind, separate from solar• Carbon Capture & Storage (CCS) for gas• Bio-energy (BE) with CCS in most runs .
• and again tries to attain more aggressive targets.
• “A Politically Feasible Architecture for Global Climate Policy: Specific Formulas and Emission Targets to Build on Copenhagen & Cancun”– with Bosetti– for the UN.
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1990 2005 2020 1990 2005 2020 1990 2005 2020 LC HC LC HC LC HC LC HC
Australia 1, 3 -5%, -15% to -25% wrt 2000 0.42 0.53 0.62 0.02 0.02 0.01 0.44 0.54 0.63 0.48 0.37 11% -15% -11% -32% -23% -41%
Belarus -5% / '-10% wrt 1990 0.14 0.08 0.10 0.00 0.00 0.00 0.14 0.09 0.10 0.13 0.13 -6% -11% 56% 48% 29% 22%
Canada -17% wrt 2005 0.59 0.73 0.83 0.02 0.04 0.04 0.62 0.77 0.88 0.65 0.65 6% 6% -16% -16% -26% -26%
Croatia -5% wrt 1990 0.03 0.03 0.04 0.00 0.00 0.00 0.03 0.03 0.04 0.03 0.03 -5% -5% -2% -2% -20% -20%
Euro 27 -20% / -30% wrt 1990 5.57 5.12 6.13 0.02 0.01 0.02 5.59 5.13 6.15 4.47 3.91 -20% -30% -13% -24% -27% -36%
Iceland -30% wrt 1990 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -30% -30% -36% -36% -44% -44%
Japan 1 -25% wrt 1990 1.27 1.35 1.54 0.02 0.02 0.02 1.29 1.38 1.57 0.98 0.98 -24% -24% -29% -29% -38% -38%
Kazakhstan 4 -15% wrt 1992 0.36 0.24 0.26 0.00 0.00 0.00 0.36 0.24 0.26 0.31 0.31 -16% -16% 29% 29% 18% 18%
New Zealand 1 -10% to -20% wrt 1990 0.06 0.08 0.09 0.00 0.00 0.00 0.06 0.08 0.09 0.06 0.05 -9% -19% -28% -36% -37% -44%
Norway -30% / -40% wrt 1990 0.05 0.05 0.06 0.00 0.00 0.00 0.05 0.05 0.06 0.03 0.03 -32% -42% -36% -46% -44% -52%
Russian Federation 1 -15% / -25% wrt 1990 3.32 2.12 2.31 0.06 0.04 0.01 3.38 2.16 2.32 2.83 2.50 -16% -26% 31% 16% 22% 8%
Switzerland -20% / -30% wrt 1990 0.05 0.05 0.06 0.00 0.00 0.00 0.05 0.05 0.06 0.04 0.04 -23% -32% -22% -31% -32% -40%
Ukraine -20% wrt 1990 0.93 0.42 0.52 0.00 0.00 0.00 0.93 0.42 0.52 0.74 0.74 -20% -20% 75% 75% 44% 44%
United States -17% wrt 2005 6.11 7.10 8.23 0.07 0.03 0.00 6.18 7.13 8.23 5.90 5.90 -5% -5% -17% -17% -28% -28%
Brazil 1, 7 -0.97 / -1.05 GtCO2-eq wrt BaU 0.72 1.11 1.53 0.89 1.45 1.13 1.61 2.56 2.66 1.68 1.61 4% 0% -34% -37% -37% -40%
China 2, 6 reduce carbon intensity of output by 40-45% wrt 2005 3.72 7.61 10.75 0.04 0.03 -0.28 3.76 7.64 10.47 10.47 10.47 179% 179% 37% 37%
India 2, 8 reduce carbon intensity of output by 20-25% wrt 2005 1.33 2.05 2.59 0.05 0.04 0.01 1.38 2.09 2.60 2.60 2.60 89% 89% 24% 24%
Indonesia 1 -26% / -41% wrt BaU 0.45 0.73 1.13 0.41 0.84 0.49 0.86 1.57 1.62 1.20 0.96 40% 12% -24% -39% -26% -41%
Mexico 1 -51 Mt CO2-eq / -30% wrt BaU 0.45 0.61 0.84 0.03 0.04 0.03 0.48 0.65 0.87 0.82 0.61 71% 27% 26% -6% -6% -30%
South Africa 1 -34% wrt BaU 0.34 0.44 0.51 0.00 0.00 0.00 0.35 0.44 0.51 0.34 0.34 -2% -2% -23% -23% -34% -34%
South Korea 1 -30% wrt BaU 0.30 0.67 0.79 0.00 0.00 0.00 0.30 0.67 0.79 0.55 0.55 84% 84% -18% -18% -30% -30%
wrt BaU (%)wrt 2005 (%)wrt 1990 (%)
Greenhouse Gases Emissions (GT CO2-eq) 11 Copenhagen Pledges 12
Country Pledge at COP15
Excluding LULUCF LULUCF Total Target
2011EU27 + 20 other countries
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Progressivity in the Cancun numbersProgressivity in the Cancun numbers setting “hot air” to 0 for 6 FSU countriessetting “hot air” to 0 for 6 FSU countries
a
a
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% cu
t wrt
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elin
e
GDP per capita
Regression line
γ =.13
t =3.9
R2=.44
Emissions
targets for 2020expressed vs. BAU(WITCH model)
Cuts ↑
The implicit progressivity coefficient is almost exactly the same as the one we had been using: .13 ≈ .14 !=> external validation of the political economy of approach
2011
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Our 12 regions:Our 12 regions:
• EUROPE = – Old Europe +
– New Europe
• US = The United States• KOSAU = Korea & S. Africa
& Australia (3 coal-users)
• CAJAZ = Canada, Japan & New Zealand
• TE = Russia & other Transition Economies
• MENA = Middle East & North Africa
• SSA = Sub-Saharan Africa• India now treated separately
• SASIA= the rest of South Asia
• CHINA = PRC
• EASIA = Smaller countries of East Asia
• LAC = Latin America & the Caribbean
2020
Figure 2: Global emission targetsFigure 2: Global emission targets resulting from the formulas & parametersresulting from the formulas & parameters
under the 500 ppm goalunder the 500 ppm goal
Using Cancun targets, near-term cuts are bigger than in our earlier work.
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Fig.3: Targets & emissions by OECD countriesFig.3: Targets & emissions by OECD countries under the 500 ppm goalunder the 500 ppm goal
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Predicted actual Predicted actual emissions exceed emissions exceed
caps, by permit caps, by permit purchases.purchases.}
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Fig.4: Targets & emissions, developing countries Fig.4: Targets & emissions, developing countries under the 500 ppm goalunder the 500 ppm goal
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Predicted actual Predicted actual emissions fall emissions fall short of caps, short of caps,
by permit sales.by permit sales.
}
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Figure 8: Effect on energy prices, Figure 8: Effect on energy prices, under 500 ppm goalunder 500 ppm goal
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Carbon Price per ton CO2 (LHS axis)
$ per gallon motor gasoline (RHS axis)
Carbon price climbs steeply in 2nd half of century,but < earlier estimates, presumably due to new technologies.
2424
Figure 5: Global economic costs Figure 5: Global economic costs (% of income) (% of income) 500 ppm goal 500 ppm goal (without BE-CCS)(without BE-CCS)
-3.5%
-3.0%
-2.5%
-2.0%
-1.5%
-1.0%
-0.5%
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0.5%
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GW
P Lo
sses Series1
Series2
Global cost < 1% of income
Contemporaneousvalue
Economic losses
Discounted at 5%
2525
USA EU KoSAu CaJaZ TE MENA SSA SAsia China EAsia LAm India
0.8%0.8% 0.4% 0.9% 0.7% 1.2% 1.2% -0.2% 0.1% 1.2% 0.9% 0.7% 0.5%0.4% 0.9% 0.7% 1.2% 1.2% -0.2% 0.1% 1.2% 0.9% 0.7% 0.5%
• Regional Cost measured with respect to baseline (no global climate policy)
• Regional Cost measured with respect to case where individual country free rides, but coalition continues.
USA EU KoSAu CaJaZ TE MENA SSA SAsia China EAsia LAm India0.7% 0.3% 0.7% 0.9% 1.6% 3.1% -0.2% -0.3% 1.2% 0.5% 0.8% 0.2%
Economic cost to each country/region (Net Present Value of income losses)
Cost is particularly high to oil producers – even if they drop out.But it is almost down to 1% even for them.
2626
Figure 7a: Economic losses of each region,Figure 7a: Economic losses of each region,relative to dropping out alonerelative to dropping out alone
(% of income)(% of income) under 500 ppm goal, 2010-2045under 500 ppm goal, 2010-2045
-1.80%
-1.60%
-1.40%
-1.20%
-1.00%
-0.80%
-0.60%
-0.40%
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0.40%
2005 2010 2015 2020 2025 2030 2035 2040 2045
USA
EU
KOSAU
CAJAZ
TE
MENA
SSA
SASIA
CHINA
EASIA
Costs stay under 2% of incomeduring the 1st half of the century.
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Figure 7b: Economic losses of each region, Figure 7b: Economic losses of each region, relative to dropping out alonerelative to dropping out alone
(% of income)(% of income) under 500 ppm goal, 2050-2090under 500 ppm goal, 2050-2090
-6.00%
-5.00%
-4.00%
-3.00%
-2.00%
-1.00%
0.00%
1.00%
2.00%
3.00%
2050 2055 2060 2065 2070 2075 2080 2085 2090
USA
EU
KOSAU
CAJAZ
TE
MENA
SSA
SASIA
CHINA
EASIAFor every country in every year,costs stay under 5% of income.
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Figure 11: Path of concentrations Figure 11: Path of concentrations hits the 500 ppm CO2 goalhits the 500 ppm CO2 goal
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First environmental goal is achieved
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Figure 12: Rise in TemperatureFigure 12: Rise in Temperatureunder the 500 ppm CO2 goalunder the 500 ppm CO2 goal
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3°C vs. 4° C under BAU
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SummarySummary• Our framework allocates emission targets across countries
in such a way that every country feels it is doing its fair share:– corresponding to what others have done before it,
• taking due account of differences in income,
– and avoiding that any country will bear a cost above threshold.• Specifically, every country expects cost < 5% GDP in every year,
– and PDV of costs of participating (almost) < 1% of GDP.
• Otherwise, announcements of distant future goals would not be credible, will not have the desired effects. – This framework—in providing for a decade-by-decade sequence of emission
targets, each determined on the basis of a few principles and formulas—– is flexible enough to accommodate changes in circumstances
during the century, by changes in the formula parameters• as more is learned about climate, economic growth, & technology.
Most relevant references by the authorMost relevant references by the author• "
Sustainable Cooperation in Global Climate Policy: Specific Formulas and Emission Targets to Build on Copenhagen and Cancun," 2011, with Valentina Bosetti. HPICA Discussion Paper No.46; FEEM Working Paper 66. Background study for Human Development Report 2011, UNDP.
• "How to Agree Emission Targets at Durban," with Bosetti, VoxEU, Nov.28, 2011.
• "Politically Feasible Emission Target Formulas to Attain 460 ppm CO2 Concentrations," with V.Bosetti; Review of Environmental Economics and Policy , Winter 2011-12; HKS RWP 11-016. From HPICA Disc.Paper 09-30.
• "An Elaborated Proposal for Global Climate Policy Architecture: Specific Formulas and Emission Targets for All Countries in All Decades,” 2009, in Post-Kyoto International Climate Policy, edited by Joe Aldy & Rob Stavins, Chapter 2, (Cambridge U. Press).
• “Formulas for Quantitative Emission Targets,” in Architectures for Agreement: Addressing Global Climate Change in the Post Kyoto World, Joe Aldy & Rob Stavins, eds., Cambridge University Press, 2007.
• "You're Getting Warmer: The Most Feasible Path for Addressing Global Climate Change Does Run Through Kyoto," FEEM, Milan, 2001. In Trade and Environment: Theory and Policy in the Context of EU Enlargement and Transition Economies, J.Maxwell & R.Reuveny, eds. (Edward Elgar , UK), 2005.
• "Greenhouse Gas Emissions," Policy Brief no. 52, The Brookings Institution,1999. 3131
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AppendicesAppendices
• 1) Trying to hit more aggressive targets
• 2) Is it economics?
• 3) Extensions for future work: Uncertainty
3333
1) 1) Bosetti-Frankel in Bosetti-Frankel in REEPREEP
• See if we can hit concentrations = 450 ppm– Assumes EU target in 2015-2020 is 30 % below
1990 levels, rather than 20 %.
– Developing country starting dates moved up.– Parameters in LCF & GEF tightened.
3434
Bottom lineBottom line
• The best we can do is attain 460 ppm
• Even then, we had to loosen our political/economic constraints:– We had to raise the threshold of costs
above which a country drops out, as high as Y =3.4% of income in PDV terms,
– and X =12 % in the worst budget period.
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Target allocations to hit goal of 460 ppmTarget allocations to hit goal of 460 ppmsource: Bosetti & Frankelsource: Bosetti & Frankel (Nov. 2009)(Nov. 2009)
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r
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EURO
KOSAU
CAJAZ
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MENA
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SASIA
CHINA
EASIA
LACA
World
Figure 2: Actual Emission per capita throughout the century, for 11 regions
3636
Figure 3:
Assigned targets & actual emissions for industrialized countries, aggregate 460 ppm (Note: Predicted actual emissions exceed caps by permit purchase amounts.)
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Figure 4: Figure 4: Assigned targets & actual emissions for poor countries, aggregateAssigned targets & actual emissions for poor countries, aggregate
460 ppm (Note: Predicted actual emissions fall below caps by permit sales amounts) 460 ppm (Note: Predicted actual emissions fall below caps by permit sales amounts)
02468
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Figure 5: Figure 5: Assigned targets & actual emissions for all countries, aggregateAssigned targets & actual emissions for all countries, aggregate
Goal: 460 ppm concentration of CO2 in year 2100 Goal: 460 ppm concentration of CO2 in year 2100
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-4.00%
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2010 2015 2020 2025 2030 2035 2040 2045
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-15.00%
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Figure 7: Income Losses by Region and Period over the Century(460 ppm)
7 b) 2050- 2100
7 a) 2010- 2045
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Figure 8: Global Income LossFigure 8: Global Income Loss
-- -- by Budget Period,by Budget Period, 2010-2100, and2010-2100, and PDV PDV (discounted to 2005)(discounted to 2005)
-4.5%
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GWP
% C
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rt B
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Discounted Global Losses (5%)
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Figure 9:Losses by Region Figure 9:Losses by Region -- PDV -- PDV (discounted to 2005 at 5% discount rate), 2010-2100(discounted to 2005 at 5% discount rate), 2010-2100
-4.0%
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USA EU KOSAU CAJAZ TE MENA SSA SASIA CHINA EASIA LAM
Net
Pre
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Figure 10: CO2 concentrationsFigure 10: CO2 concentrations
to achieve year-2100 goal of 460 ppmto achieve year-2100 goal of 460 ppm
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Figure 11: Rise in temperature Figure 11: Rise in temperature
under proposed targets (460ppm) vs. BAUunder proposed targets (460ppm) vs. BAU
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Even though the 460 ppm target is achieved by mid-century, the pay-off in further temperature moderation, relative to 500 ppm, is not large. There are diminishing returns to CO2 abatement in two senses: The marginal cost of abatement rises in dollar terms, and the marginal cost of temperature moderation rises in terms of CO2.
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Figure A1. Choosing country targets to minimize threshold for PDV country costs
loses the simplicity of a common formula for all,(green triangles)
without much gain in reducing PDV of global losses
0.00%
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Figure A2. Varying the developing country start dates
tightens or loosens the CO2 concentration objective(blue diamonds)
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ConclusionsConclusions
• Some may conclude that the goals of 380 or 450 ppm in CO2 concentrations are not attainable in practice, – and that our earlier proposal for 500 ppm
is the better plan (Frankel, 2009). – We take no position on the best environmental goal. – Rather, we submit that, whatever the goal,
our formulas will give targets that are more practical economically and politically than approaches that have been proposed by others.
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Appendix 2:“Is it economics?”Appendix 2:“Is it economics?”• Define economics as maximization
of objectives subject to constraints.
• That applies not just to private agents maximizing expected utility subject to budget constraints,
• but also to how policy-makers can maximize objectives subject to political constraints.
• Not the same as what other climate modelers do:– cost-benefit analysis (Integrated Assessment models),
– or minimizing economic costs subject to the constraint of attaining a given environmental goal.
Appendix 3: UncertaintyAppendix 3: Uncertainty
• The next phase of our research allows for uncertainty– in baseline economic growth– In carbon-saving technological progress– In environmental goals that the politics support
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Two separate motivations to allow for uncertaintyTwo separate motivations to allow for uncertainty
• (1) Some readers don’t believe cost estimates– from WITCH or other models
• saying they are too high• or too low.
– Allowing for true year-2050 parameters that differ from current assumptions
• readers can see how much difference it makes.• Lesson: Just get started !
– Decade-by-decade political sustainability constrains numerical target choices far more than discount rate calculations
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Two separate motivations to allow for uncertainty, Two separate motivations to allow for uncertainty, continuedcontinued
• (2) The political sustainability constraint that requires loss X loss X << 5% 5% GDP,GDP, for every country for every country in every period, becomes harder to satisfy.in every period, becomes harder to satisfy.
• Requires using the flexibility that is built in Requires using the flexibility that is built in to our target-formulas framework:to our target-formulas framework:– Negotiators update parameters periodically, Negotiators update parameters periodically,
• in line with developmentsin line with developments
– Express within-decade targets as indexed to GDPExpress within-decade targets as indexed to GDP– perhaps proportionately (“intensity targets”)perhaps proportionately (“intensity targets”)
– Perhaps allow “escapePerhaps allow “escape clauses” clauses” if cost of carbon too high or lowif cost of carbon too high or low
5050
Papers aPapers available at: http://ksghome.harvard.edu/~jfrankel/currentpubsspeeches.htm On Climate Changevailable at: http://ksghome.harvard.edu/~jfrankel/currentpubsspeeches.htm On Climate Change
