The case for Geoengineering Research MIT 30 October 2009 Cambridge, MA David Keith keith@ucalgary.ca • www.ucalgary.ca/~keith Director, Energy and Environmental Systems Group Institute for Sustainable Energy, Environment and Economy University of Calgary 1 1
We can & must stop emissions Example: Electricity accounts for 40% of global emissions We can make near ‐ zero emissions power today. With strong cost ‐ effective policy we could decarbonize electricity production within a quarter century. Technologies that are ready to go at reasonable cost now: • Wind power (with backup & long distance transmission) • Nuclear power • Coal with CO 2 capture and storage • Central ‐ station solar thermal (with long distance transmission) Cost: a few % of GDP. In the rich countries that is: • Similar to the cost of all other environmental controls • A bit bigger that current military spending • Many times smaller than the cost of health care • A good year’s GDP growth 2
Climate impact Human actions that Climate change climate on human welfare System Mitigation Geoengineering Adaptation 3
Solar radiation management ≠ Carbon cycle engineering Solar radiation management (SRM) Carbon cycle engineering (CDR) • Sulfates in the stratosphere • Biomass + CCS • Sea salt aerosols in low clouds • Direct capture of CO 2 from air • Altering plant albedo • Adding Fe to oceans • Engineered particles in mesosphere • Adding macro ‐ nutrients to oceans • Adding alkalinity (Mg) to oceans • Bio ‐ char • Adding alkalinity to soils Fast, cheap, imperfect and Slow and expensive , uncertain ; and it does very but it gets the carbon out little to manage the carbon in the air 4
Cheap, Fast and Imperfect Cheap Aerosol mass flux needed to create 4 Wm ‐ 2 radiative forcing: of ≈ 1 μ m aerosol into marine stratus clouds. 3×10 4 kg sec ‐ 1 • of S ≈ 0.2 μ m sulfate aerosol into the stratosphere. 150 kg sec ‐ 1 • Comparison 2.6×10 6 kg sec ‐ 1 (4 Wm ‐ 2 ) † • CO 2 mass flux required to remove 2000 Gt ‐ CO 2 in 25 years. Fast Aerosols radiative forcing acts on timescales of days (troposphere) to years (stratosphere). Comparison • Cutting emissions to zero stops concentration increase CO 2 but does (almost) nothing for the CO 2 already emitted. Economic inertia + carbon cycle inertia � century long response times • 5
Cheap, Fast and Imperfect Imperfect Reducing insolation ≠ Decreasing CO 2 Reducing insolation � less energy input to the surface � less flux from surface to mid troposphere � weaker hydrological cycle Increasing CO 2 � cooler troposphere & warmer stratosphere Decreasing insolation � cooler troposphere & stratosphere Decreasing insolation � no direct reduction in geochemical impacts of CO 2 . 6
Timescales and inertia: carbon and sunlight 7
Business as usual Strong climate policy MIT, Center for Global Change Studies (2009) 8
1.0 Given 4 C global @ 2100 Greenland only 0.8 Marshal & Keith DV 0.6 ER JO TP vanderveen 0.4 clarkeg vanderwaal bindschadler greve 0.2 truffer Morgan & Keith (1995) bamber calov ritz 0.0 0 1 2 3 4 Forest et al (2002) 9
Inertia: CO 2 lasts longer than nuclear waste If we instantly stop emissions of CO 2 temperatures remain high for millennia • 10,000 years after emissions stop, CO 2 concentrations and warming will be about 1/2 to 1/3 the level they were on the day the coal plants shut down. The fission products in nuclear waste are gone in about 1000 years. • 10,000 years after discharge nuclear waste is 3000 times less radioactive than it was one year after it left the reactor. dioxide emissions, PNAS, 106, 1704–1709. Solomon et al (2009) Irreversible climate change due to carbon MIT Study on the Future of Nuclear Power (2003) 3000 × 10
Inertia Turn wheel (e.g., enact policy) Low emissions infrastructure is built at some rate after a time delay Emission reductions grow as the integral of the infrastructure build rate . Concentration reductions grow as the integral of emissions reductions. Reduction in temperature (from BAU) responds more slowly that reduction in concentrations due to ocean thermal inertia Climate reacts Uncertainty + Inertia = Danger 11
Physical ‐ science research for solar radiation management 12
Stratospheric scatterers Of order 2 ‐ 4 Mt ‐ S per year offsets the radiative forcing of 2 × CO 2 (~5% of current global S emissions, assuming fine ‐ mode particles) ~3 gram sulfur in the stratosphere roughly offsets 1 ton carbon in the atmosphere (S:C ~ 1:200,000) 10 $/kg � 10’s of $bn per year ≈ 0 � Cost not the deciding issue. Risk to risk. Alternative scattering systems Lofting methods: Oxides • Aircraft • H 2 SO 4 or Al 2 O 3 • Naval guns Metallic particles (10 ‐ 10 3 × lower mass) • Tethered balloon with a hose • Disks, micro ‐ balloons or gratings Resonant (10 4 ‐ 10 6 × lower mass ??) Scattering design goals: • Encapsulated organic dyes • Lower mass Self ‐ lofting particles • Spectral selectivity • Photophoresis. • Altitude selectivity • Direct: diffuse selectivity 13 • Latitude selectivity
Physical ‐ science research needs 0. Assessing climate response to solar radiation management. 1. Assessing the utility of sub ‐ scale experiments • How small a perturbation (sulfate loading) can be detected over a given observational period? • How does SNR vary with modulation frequency and location? • What can we say about the ability to detect side ‐ effects and problems? 2. Getting ready for the next big volcano • What instrumentation and research planning is needed to take best advantage of an eruption that puts Mt of S in the stratosphere? 3. Understanding and engineering the plume ‐ scale dispersal of sulfates. 4. Engineering system studies of stratospheric delivery systems. 5. Engineering dispersal systems and operational strategies for sea ‐ salt aerosols. 6. Non ‐ sulfate aerosols or engineered particles in the upper atmosphere. 14
Aerosol dynamics: AER ‐ ETH results 2D AER sulfate model (see below) First look at sulfate geoengineering with a model that does prognostic aerosol dynamics. Figure credits: Debra Weisenstein (AER) and Thomas Peter (ETH) 15
Sulfur questions What are we injecting: H 2 S? SO 2 , S? H 2 SO 4 ? If H 2 S then local dispersal does not matter since H 2 S must be oxidized before aerosol dynamics start. • H 2 S injections end up being deposited on the large end of the particle size distribution � very inefficient. • Generalize to any gas phase injection? If we are injecting S or H 2 SO 4 then result will depend on dynamic competition between nucleation and turbulent mixing in aircraft wake. Essentially no work as been done to look at engineering of injection systems. 16
Measuring the effectiveness of SRM Most model experiments to date compare pre ‐ industrial with 2×CO 2 plus SRM sufficient to bring surface temps back to pre ‐ industrial means. ‐ It has become common to talk about the 2×CO 2 plus SRM pre ‐ industrial differences, particularly precipitation differences as the “impacts” of SRM. There are several problems with this: 1. This would make sense if it were 1800 and we were analyzing the choice to burn a few 1000 Gt ‐ C and compensate its worst effects with SRM. 2. SRM reduces precip more strongly than it reduces precip ‐ evap. Quantities like soil moisture are more relevant to assessing impacts. 3. Analysis of CO 2 ‐ driven climate impacts has identified variability as a crucial driver, and one might expect precip variability to be reduced in high ‐ CO 2 low ‐ insolation world. Clarity about language: Impacts or side ‐ effects = ozone chemistry, rain out of particles into troposphere. Imperfection or ineffectiveness = the fact that SRM climate change not same as CO 2 17
Temperature and Precipitation Changes Under Variable SRM Precip and Temp changes scaled to standard deviation of pre-industrial climate 18 Ricke, Morgan and Allen, submitted to Nature
Research strategy: How to balance the research portfolio? Ease of Funding: • Carbon capture via bio ‐ char burial Easy • Climate model studies of the impacts/effectiveness of SRM. • Economics, risk assessment, public policy analysis of SRM. • Engineering design of hardware for sea salt aerosols. • Engineering studies of stratospheric scattering systems: production, dispersal, and delivery of sulfate (or other) aerosols. Micro ‐ scale field testing of sea salt aerosols. • Micro ‐ scale field testing of sulfate dispersal systems. • Difficult Balancing critics & engineers “It’s vital to have this “red team” of skeptics questioning geo ‐ engineering. But we need more emphasis on a “blue team” to figure out what geo ‐ engineering approaches might work” ‐‐ Homer ‐ Dixon & Keith. NYT Op ‐ Ed, 19 September 2008 19
20 Credit: Novim
Valuing information 21
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