1 Impact of geoengineering aerosols on stratospheric temperature and ozone Tom Peter, ETH Zurich, Switzerland “Anthropogenically enhanced sulfate particle concentrations … cool the planet, offsetting a … fraction of the anthropogenic increase in green- house gas warming. … This creates a dilemma for environmental policy makers, because the required emission reductions of SO 2 …, as dictated by health and ecological considerations, add to global warming. By far the preferred way to resolve the policy makers’ dilemma is to lower the emissions of the greenhouse gases. However, so far, attempts in that direction have been grossly unsuccessful …” Paul J. Crutzen: ‘Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma?’, Climatic Change, 2006

2 Morton, Nature Tg S stratospheric burden:  average optical depth  ~1 ppbV sulfur (6  natural)  W/m 2 downscaling effect by Mt. Pinatubo: 10 TgS injected into stratosphere [Bluth et al. 1992], after 6 month the remaining 6 TgS caused 4.5 W/m 2 radiative cooling [Hansen et al. 1992] 1-2 Tg S stratospheric burden needed to compensate 1.4 W/m 2 RF expected from cleaning the air (global brightening) [Crutzen and Ramanathan, 2003] 5.3 Tg S stratospheric burden needed to compensate 4 W/m 2 RF expected from CO 2 doubling [Crutzen, 2006] Geoengineering THE GEOENGINEERING DILEMMA: TO SPEAK OR NOT TO SPEAK?

3 Assumptions made previously on particle sizes of geoengineering aerosols Crutzen, Climatic Change, 2006: … the particle sizes of the artificial aerosols are smaller than those of the volcanic aerosol, because of greater continuity of injections in the former … Rasch et al., GRL, 2008 … we have explored scenarios spanning much of the size range that the aerosols might attain, assuming the distribution will either be ‘‘small’’, like that seen during background situations with volcanically quiescent conditions, or ‘‘large’’ like 6–12 months after an eruption … Robock et al., JGR, 2008 …we define the dry aerosol effective radius as 0.25  m, compared to 0.35  m for our Pinatubo simulations… Heckendorn et al., ERL,2009 (under review) … in contrast to all previous work the particles are predicted to grow to larger sizes than observed after volcanic eruptions…

4 Compare volcanic eruption and geoengineering Use AER 2D aerosol model input to CCM SOCOL Volcanic eruption: 1 single SO 2 injection Geoengineering: continuous SO 2 emissions Formation of larger aerosol particles Pina10: 10 Mt S in June Mt S in January 1992 Geo0, Geo1, Geo2, Geo5, Geo10 1 Mt 2Mt 5Mt 10Mt S/a Geo0 Geo1 Geo2 Geo5 Geo10 Pina10

5 Nonlinear injection-burden relationship Total amount of S in the condensed phase: coag/10 2x/yr no sedimentation Rasch et al., GRL 2008 Nonlinear dependence on annual sulfur injections Larger injections lead to more efficient coagulation Partial compensation by less frequent injections Sedimentation lowers loading by ~3/4 Potential repercussions: Warmer tropopause Moister stratosphere Changed dynamics More ozone loss Close investigation required.

6 Nonlinear injection-burden-radiation relationship Total amount of S in the condensed phase: Nonlinear dependence on annual sulfur injections Larger injections lead to more efficient coagulation Partial compensation by less frequent injections Sedimentation lowers loading by ~3/4 Potential repercussions: Warmer tropopause Moister stratosphere Changed dynamics More ozone loss Close investigation required.

7 Impact on ozone layer  1/3 of the ozone loss caused by radiative effects (temperature increase and HO x increase)  2/3 of the ozone loss caused by enhanced heterogeneous reactions on the aerosols  Ozone loss due to geoengineering could be of the same magnitude as due to ODS (ozone depleting substances)  Especially near the main aerosol cloud and in the polar region massive ozone loss must be anticipated Geo5 Geo5 no radiation Geo5 no chemistry Change in total ozone column Scenario nameOzone change Geo % -6.9 DU Geo % -9.4 DU Geo % DU Geo % DU Geo5 no radiation -3.2 % -9.7 DU Geo5 no chemistry -1 % -2.9 DU

8 Modeled ozone after Pinatubo eruption Geo1 Geo2 Geo5 Geo10 Unperturbed SAGE1.8_1 Pina7 Pina13

9 Risks of Climate Engineering Gabriele C. Hegerl and Susan Solomon (Science, Perspective, 2009) “Blackstock et al. call for a study phase, during which the possible impacts of geoengineering options could be investigated. This is clearly necessary, and optimism about a geoengineered »easy way out« should be tempered by examination of currently observed climate changes. …” Climate Engineering Responses to Climate Emergencies Jason Blackstock and collegues (Novim, Santa Barbara, CA, 2009) “… climate engineering concepts … could serve as a rapid palliative response to near-term climate emergencies ….”

10 The ROYAL SOCIETY Strictly Embargoed Until 1 st September BST Stop emitting CO 2 or geoengineering could be our only hope The future of the Earth could rest on potentially dangerous and unproven geoengineering technologies unless emissions of carbon dioxide can be greatly reduced, the latest Royal Society report has found. Geoengineering technologies were found to be very likely technically possible and some were considered to be potentially useful to augment the continuing efforts to mitigate climate change by reducing emissions. However, the report identified major uncertainties regarding their effectiveness, costs and environmental impacts. Geoengineering THE GEOENGINEERING DILEMMA: TO SPEAK OR NOT TO SPEAK?

11 Key recommendations on geoengineering: (1)Mitigation/adaptation: Parties to the UNFCCC should: (a)increase efforts towards mitigatinon/adaption (b)agree to global emissions reductions of at least 50% by 2050 (2)Governance: To ensure that geoengineering methods can be adequately evaluated, and applied responsibly and effectively should the need arise, introduce three priority programs: (a)internationally coordinated research and development on the more promising methods (b)international collaborative activities to explore the feasibility, benefits, environmental impacts, risks and opportunities (c)development and implementation of governance frameworks to guide research and development in the short term, and possible deployment in the longer term, including a public dialogue process (3)High Commission: The governance challenges should be explored in more detail by an international body such as the UN Commission for Sustainable Development

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13 Ethical caveats remain! They call for not applying geoengineering, maybe even for not doing exploratory research on geoengineering. How serious are they? (1) The scientific thought process cannot not be reversed, not even be stopped! (2) Global warming was unintentional. But is today’s continuation of it still “unintentional”? Or just “unavoidable”? Or not even this, rather just common practice? (3) Could a united opinion of scientists worldwide keep us all from abusing geoengineering – or is this just a naïve conception? Geoengineering THE GEOENGINEERING DILEMMA: TO SPEAK OR NOT TO SPEAK?

14 Geoengineering THE GEOENGINEERING DILEMMA: TO SPEAK OR NOT TO SPEAK? Should SPARC proceed as we would on any other scientific problem, at least for theoretical and modeling studies? Cons: It is scientifically not feasible, it distracts from the actual problem (reducing GHGs), it channels the resources into the wrong direction, it gives the wrong sign to politicians, it has unbearable political/social/ legal consequences (winners/losers), it can’t be done “right” anyway. Pros: The scientific thought process cannot not be stopped, we need to acquire the knowledge, we should influence the outcome, we should help doing it “right” – also if this results in doing it not at all.

15 Discussed in Bremen, but not approved: SPARC SSG Position Statement on Geoengineering Injection of sulfur into the lower stratosphere has been suggested as a strategy to reduce global warming caused by greenhouse gases. However, current knowledge on the efficiency of such an action and on its potentially significant unintended side-effects is lacking. Such side-effects include … [list]. Therefore comprehensive modeling investigations into geo-engineering options must be undertaken before any sort of geoengineering options could be considered for application. At the same time we would be mislead if such work was leading to a weakening of scientific efforts to investigate the primary driver of climate change, let alone if it slowed the international climate negotiations.

16 SPARC – Where do we go from here?

17 You asked about Geoengineering: My thoughts on this issues have evolved a little but it is pretty similar to what I said (after correcting my statements for misunderstandings due to my poor expressions!!) in Bremen. I still do not think that SPARC should have an official position on doing Geoengineering. However, it is vital for organizations such as SPARC to facilitate research that clarifies the benefits, dis-benefits, unintended consequences, feasibility, and other issues. Now that I have attended some workshops on this issue and taken part in many discussions as a part of writing the US National Academy Sciences' "America's Climate Choices," I believe that science is only one component of this issue- other considerations such as ethics, international responsibilities, legalities, etc are very important for even trying out these solutions on a small scale, if it involves offsetting the effects of increasing greenhouse gases. I will be happy to talk more about it, if it helps....

18 CO 2 abatement Albedo engineering CO 2 engineering Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000) Geoengineering Cost TechnicalRisk of side Nontechnical method $/tCuncertaintieseffects issues Injection of CO Less uncertainty Low risk Geoengineering or abate- underground than oceanic storage ment? Possibility of leakage? Injection of CO Some uncertaintyLow risk. Damage to Legal and political concerns: into the ocean about fate of CO 2 benthic ecosystem? London Dumping Convention Intensive forestry, Uncertain rateLow risk. Impact on Political questions: how to harvested trees of C capturesoil and biodiversity? divide costs? Whose land? Ocean fertilization 3-10 Can ecosystem alter Moderate risk. O 2 Legal concerns: Law of the with phosphate or P:N utilization ratio?depletion? Biota Sea, Antarctic Treaty. ironLong-term capture?change? CH 4 release? Effects on fishery? Space-borne Uncertain costs and Low risk. Security, equity and liability solar shieldstechnical feasibility Albedo   CO 2  if used for weather control Stratospheric SO 2 : << 1 Uncertain lifetime High risk. Effect on O 3. Liability: ozone destruction direct light scatteringof aerosolsAlbedo   CO 2  Tropospheric aerosol: < 1Problem of aerosolModerate risk. Unin- Liability and sovereignty direct light scattering transport and tentional in progress. because aerosol distribution and cloud reflectivitychanged cloudinessAlbedo   CO 2  affects regional climate Emission abatement > 50 % abatementNo climate risk Who starts? Kyoto problem Business as usual Costs uncertain,Treat risk explicitly, In many sectors social costs Stern Rev. 300 $/tClow-prob/hi-impact? higher than marginal costs

19 CO 2 abatement Albedo engineering CO 2 engineering Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000) Geoengineering Cost TechnicalRisk of side Nontechnical method $/tCuncertaintieseffects issues Injection of CO Less uncertainty Low risk Geoengineering or abate- underground than oceanic storage ment? Possibility of leakage? Injection of CO Some uncertaintyLow risk. Damage to Legal and political concerns: into the ocean about fate of CO 2 benthic ecosystem? London Dumping Convention Intensive forestry, Uncertain rateLow risk. Impact on Political questions: how to harvested trees of C capturesoil and biodiversity? divide costs? Whose land? Ocean fertilization 3-10 Can ecosystem alter Moderate risk. O 2 Legal concerns: Law of the with phosphate or P:N utilization ratio?depletion? Biota Sea, Antarctic Treaty. ironLong-term capture?change? CH 4 release? Effects on fishery? Space-borne Uncertain costs and Low risk. Security, equity and liability solar shieldstechnical feasibility Albedo   CO 2  if used for weather control Stratospheric SO 2 : << 1 Uncertain lifetime High risk. Effect on O 3. Liability: ozone destruction direct light scatteringof aerosolsAlbedo   CO 2  Tropospheric aerosol: < 1Problem of aerosolModerate risk. Unin- Liability and sovereignty direct light scattering transport and tentional in progress. because aerosol distribution and cloud reflectivitychanged cloudinessAlbedo   CO 2  affects regional climate Emission abatement > 50 % abatementNo climate risk Who starts? Kyoto problem Business as usual Costs uncertain,Treat risk explicitly, In many sectors social costs Stern Rev. 300 $/tClow-prob/hi-impact? higher than marginal costs

20 CO 2 abatement Albedo engineering CO 2 engineering Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000) Geoengineering Cost TechnicalRisk of side Nontechnical method $/tCuncertaintieseffects issues Injection of CO Less uncertainty Low risk Geoengineering or abate- underground than oceanic storage ment? Possibility of leakage? Injection of CO Some uncertaintyLow risk. Damage to Legal and political concerns: into the ocean about fate of CO 2 benthic ecosystem? London Dumping Convention Intensive forestry, Uncertain rateLow risk. Impact on Political questions: how to harvested trees of C capturesoil and biodiversity? divide costs? Whose land? Ocean fertilization 3-10 Can ecosystem alter Moderate risk. O 2 Legal concerns: Law of the with phosphate or P:N utilization ratio?depletion? Biota Sea, Antarctic Treaty. ironLong-term capture?change? CH 4 release? Effects on fishery? Space-borne Uncertain costs and Low risk. Security, equity and liability solar shieldstechnical feasibility Albedo   CO 2  if used for weather control Stratospheric SO 2 : << 1 Uncertain lifetime High risk. Effect on O 3. Liability: ozone destruction direct light scatteringof aerosolsAlbedo   CO 2  Tropospheric aerosol: < 1Problem of aerosolModerate risk. Unin- Liability and sovereignty direct light scattering transport and tentional in progress. because aerosol distribution and cloud reflectivitychanged cloudinessAlbedo   CO 2  affects regional climate Emission abatement > 50 % abatementNo climate risk Who starts? Kyoto problem Business as usual Costs uncertain,Treat risk explicitly, In many sectors social costs Stern Rev. 300 $/tClow-prob/hi-impact? higher than marginal costs

21 CO 2 abatement Albedo engineering CO 2 engineering Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000) Geoengineering Cost TechnicalRisk of side Nontechnical method $/tCuncertaintieseffects issues Injection of CO Less uncertainty Low risk Geoengineering or abate- underground than oceanic storage ment? Possibility of leakage? Injection of CO Some uncertaintyLow risk. Damage to Legal and political concerns: into the ocean about fate of CO 2 benthic ecosystem? London Dumping Convention Intensive forestry, Uncertain rateLow risk. Impact on Political questions: how to harvested trees of C capturesoil and biodiversity? divide costs? Whose land? Ocean fertilization 3-10 Can ecosystem alter Moderate risk. O 2 Legal concerns: Law of the with phosphate or P:N utilization ratio?depletion? Biota Sea, Antarctic Treaty. ironLong-term capture?change? CH 4 release? Effects on fishery? Space-borne Uncertain costs and Low risk. Security, equity and liability solar shieldstechnical feasibility Albedo   CO 2  if used for weather control Stratospheric SO 2 : << 1 Uncertain lifetime High risk. Effect on O 3. Liability: ozone destruction direct light scatteringof aerosolsAlbedo   CO 2  Tropospheric aerosol: < 1Problem of aerosolModerate risk. Unin- Liability and sovereignty direct light scattering transport and tentional in progress. because aerosol distribution and cloud reflectivitychanged cloudinessAlbedo   CO 2  affects regional climate Emission abatement > 50 % abatementNo climate risk Who starts? Kyoto problem Business as usual Costs uncertain,Treat risk explicitly, In many sectors social costs Stern Rev. 300 $/tClow-prob/hi-impact? higher than marginal costs