Stabilization and Global Climate Policy in a Multi-Gas World Marcus C Sarofim*, Chris E Forest*, David M Reiner † , John M Reilly* *Joint Program on the Science and Policy of Global Change, MIT † Judge Institute of Management Studies, Cambridge University NIES and EMF Stabilization Workshop Tsukuba, Japan, Jan. 22-23, 2004
Aim of the Research • To examine the issues involved in current discussions of stabilization policy given a multi-greenhouse gas world – To encourage tighter definition of stabilization in academic and political discussion. – To reemphasize the importance of non-CO 2 greenhouse gases for effective, inexpensive temperature reduction on the two century time scale. – To examine stabilization under uncertainty.
Article 2 of the Framework Convention on Climate Change • “The ultimate objective of this Convention... is to achieve... stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt... to ensure that food production is not threatened, and to allow economic development to proceed in a sustainable manner.”
Definitions of Stabilization • Many anthropogenic greenhouse gases exist: – CO 2 , CH 4 , N 2 O, SF 6 , HFCs, etc. – Not including “climatically important substances” such as SO 2 , black carbon, ozone precursors, etc. • Stabilize CO 2 only? (EU 550 ppm position) – What are assumptions about other gases? – SRES A1B is often used for non- CO 2 gases. • Stabilize overall radiative forcing? – Separate targets for each gas? CO 2 equivalents? • Trading between gases? – The use of Global Warming Potentials (GWPs) is incompatible with stabilization. • When? 2100? 2150? 2500? 3000?
Nature of Two Scenarios: CO2ONLY and GHGTRADE • Estimate cumulative CO 2 emissions to 2100 consistent with ‘stabilization’ of CO 2 at 550 ppm – Actually 530 ppm in 2100 to allow for gradual stabilization after 2100. • Allocate CO 2 reductions optimally over time. – Discounted marginal abatement equalized over time— price rises at the discount rate. • Expand constraint to Other GHGs – Allow GHG trading using 100-year GWP to achieve reductions equal to CO 2 only case – Considered proportional reduction case (not shown)
Considerations • Emissions path consistent with a frequently discussed policy target, reinterpreted in multigas terms. – Other interpretations possible. • Economic rationale for initial allocation of reductions over time – but once expanded to other GHGs its no longer quite true • Known concentration and climate outcomes associated with these emissions scenario • Economic and climate outcomes are true for EPPA/MIT IGSM—not necessarily for other models.
Further Considerations • Initial CO 2 path was achieved with a globally uniform carbon tax– equal marginal costs. • After adding other GHGs, reinterpreted as a quantity constraint • Concentration and climate effects depend little on the regional allocation – Regionally reallocate global totals as desired, and still be consistent with concentration and climate results.
EPPA: An Economic/Emissions Model • CGE model of the world economy with all human activities and all CIS’s. – GHGs: CO 2 , CH 4 , N 2 O, SF 6 , PFC, HFC . – Other air pollutants: NO X , SO X , CO, NMVOC, NH 3 and carbonaceous particulates. – Activities: Energy combustion and production, agriculture and land use, industrial processes, waste disposal (sewage & landfills). • Designed for the 100 year time scale.
Emission paths (550 ppm) Methane Path Carbon Path 30 1000 900 BAU 25 800 700 CO2ONLY BAU 20 600 Tg CH4 GtC/year 500 15 400 GHGTRADE 10 300 GHGTRADE 200 CO2ONLY 5 100 0 0 2000 2020 2040 2060 2080 2100 2000 2020 2040 2060 2080 2100 Year Year
The MIT IGSM A coupled chemistry, climate, ocean, and ecosystem model.
Some Aspects of the MIT IGSM • Natural systems (ocean and terrestrial) integrated part of the coupled atmosphere-ocean model – ocean and terrestrial biology of C uptake – natural CH 4 , N 2 O, C affected by climate and atmospheric concentrations of CO 2 • Carbon from human land use assumed to be neutral over the century • Active and integrated atmospheric chemistry resolved for urban and rural conditions – Tropospheric ozone as an additional warming effect – Sulfate aerosols as cooling effect – Oxidation of CH 4 explicit so lifetime is endogenous
Total GHG Forcing (change since 1990) 8 ∆ total forcing since 1990 (W/m 2 ) 7 6 BAU 5 CO2ONLY 4 3 GHGTRADE 2 1 0 2000 2020 2040 2060 2080 2100 Year
Results in 2100 Temperature Reduction in Reduction Net Present Consumption (From 2.8 ºC) CO2ONLY 0.75 ºC 1.2% GHGTRADE 1.18 ºC 0.5%
Long Term Studies (to 2300) 3 1.2 Temperature change since 1990 (ºC) Sea level rise since 1990 (m) 2.5 1 2 0.8 1.5 0.6 1 0.4 CO2ONLY Temperature GHGTRADE Temperature 0.5 0.2 CO2ONLY Sea Level Rise GHGTRADE Sea Level Rise 0 0 2000 2050 2100 2150 2200 2250 2300 Year
Uncertainty in Policy Costs 1 Cumulative probability density 0.9 0.8 0.7 0.6 CO2ONLY: Mean 1.1 5/95 bounds: 0.02 / 3.9 0.5 0.4 0.3 GHGTRADE: Mean 0.67 0.2 5/95 bounds: 0.01 / 2.6 0.1 0 0 1 2 3 4 5 6 Percentage Loss of Net Present Consumption
Uncertainty in Climate System Parameters 550 ppm CO2ONLY emissions scenario 1.8 0.9 1.6 0.8 Probability Density (x 10 -2 ) 1.4 0.7 Probability Density 1.2 0.6 1 0.5 0.8 0.4 0.6 0.3 0.4 0.2 0.2 0.1 0 0 490 540 590 0 1 2 3 4 CO 2 concentration (ppm) Temperature Rise from 1990 (°C)
Carbon Uptake 550 ppm CO2ONLY emissions scenario 10 600 9 CO 2 concentration 500 8 7 Carbon emissions 400 Pg C/year 6 ppm CO 2 5 300 4 200 Ocean uptake Total uptake 3 2 CO 2 emissions 100 1 Terrestrial uptake 0 0 2000 2050 2100 2150 2200 2250 2300 Year
CAVEATS • Modeling – Results depend heavily on abatement curves and technology assumptions in model. – Discount rate impacts emissions path and cost calculations: Absolute numbers but not conclusions are sensitive to choice of rate. • Policy Implementation – Non-CO 2 sources are hard to monitor. – Reducing CO 2 emissions may require capital investments which should be started early.
Future Work • Uncertainty: – Impact of other gas emission uncertainty on global temperature change results. – Determining carbon emissions pathways given carbon uptake uncertainty. – Tradeoffs between cost and damages. • Policy Improvements – Devising an “optimum cost over time” all-GHG policy. – More realistic policies: developing countries should have differentiated goals.
Conclusions • Stabilization of carbon dioxide concentrations can be met at reasonable costs. However, these costs will be much less if trading is allowed between all gases. Additionally, an all-gas policy is much more effective than CO 2 only policies on the two century scale. • Uncertainty in costs and uncertainty in impacts should be incorporated into the determination of appropriate targets. • Imprecision in language should be addressed before creating long term policy frameworks.
Carbon-Equivalent Prices 2005-2050 300 Year 2005 Prices: Cost of Carbon (1995 US $/ton C eq) $30.48 250 $1.46 200 150 All GHG 100 Proportional CO 2 only 50 0 2000 2010 2020 2030 2040 2050 Year
Total GHG Emissions, GWP weighted Carbon equivalents by GWP (Gt C) 35 30 Reference 25 20 CO 2 only GWP Equiv. 15 10 All GHG Proportional Reduction 5 0 2000 2020 2040 2060 2080 2100 Years
Total Carbon Emissions 25 Reference 20 CO 2 emissions (Gt C) 15 GWP Equivalent 10 CO 2 only Proportional 5 Reductions 0 2000 2020 2040 2060 2080 2100 Year
Total Methane Emissions 1000 Reference 900 800 CH 4 emissions (MT) CO 2 only 700 600 500 All GHGs GWP equivalent 400 300 All GHGs 200 Proportional Reductions 100 0 2000 2020 2040 2060 2080 2100 Year
CO 2 Concentrations 800 CO 2 Concentration (ppm) 700 A ll GHGs GWP Eq. 600 Reference 500 CO 2 only 400 All GH Gs Proportional 300 2000 2020 2040 2060 2080 2100 Year
Methane Concentration 6 Reference 5 4 Concentration (ppm) 4 CO 2 only 3 All GHGs GWP equivalent 2 All GHGs CH Proportional Reductions 1 0 2000 2020 2040 2060 2080 2100 Year
Total N 2 O Emissions 25 20 Reference N 2 O Emissions (Tg) 15 CO 2 only All GHGs 10 GWP equivalent All GHGs 5 Proportional reduction 0 2000 2020 2040 2060 2080 2100 Year
N 2 O Concentration 500 480 N 2 O Concentration (ppb) 460 440 Reference CO 2 only 420 400 GWP eq. 380 360 All GHGs 340 Proportional reduction 320 300 2000 2020 2040 2060 2080 2100 Year
Ozone Concentration 55 50 O 3 concentration 45 40 35 30 2000 2020 2040 2060 2080 2100 Year
Global Mean Temperature Change: 2000-2100 3 Mean Temperature Change 2.5 Reference from 1990 (°C) 2 CO 2 only 1.5 1 All GHGs 0.5 Proportional Reduction 0 2000 2020 2040 2060 2080 2100 Year
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