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Impact of geoengineering aerosols on stratospheric temperature and ozoneTom 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 SO2 …, 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

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Morton, Nature 2007

1 Tg S stratospheric burden: 0.007 average optical depth

~1 ppbV sulfur (6 natural) -0.75 W/m2

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/m2 radiative cooling [Hansen et al. 1992]

1-2 Tg S stratospheric burden needed to compensate 1.4 W/m2 RF expected from cleaning the air

(global brightening)

[Crutzen and Ramanathan, 2003]

5.3 Tg S stratospheric burden needed to compensate 4 W/m2 RF

expected from CO2 doubling[Crutzen, 2006]

GeoengineeringTHE GEOENGINEERING DILEMMA: TO SPEAK OR NOT TO SPEAK?

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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…

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Compare volcanic eruption and geoengineeringUse AER 2D aerosol model input to CCM SOCOL

Volcanic eruption:1 single SO2 injection

Geoengineering:continuous SO2 emissions

Formation of larger aerosol particles

Pina10: 10 Mt S in June 1991 7 Mt S in January 1992

Geo0, Geo1, Geo2, Geo5, Geo10 1 Mt 2Mt 5Mt 10Mt S/a

Geo0Geo1Geo2Geo5

Geo10Pina10

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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 lossClose investigation

required.

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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 lossClose investigation

required.

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Impact on ozone layer

1/3 of the ozone loss caused by radiative effects (temperature increase and HOx 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

Geo5Geo5 no radiation

Geo5 no chemistry

Change in total ozone column

Scenario name Ozone change

Geo1 -2.3 % -6.9 DU

Geo2 -3.1 % -9.4 DU

Geo5 -4.5 % -13.5 DU

Geo10 -5.3 % -15.9 DU

Geo5 no radiation -3.2 % -9.7 DU

Geo5 no chemistry

-1 % -2.9 DU

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Modeled ozone after Pinatubo eruption

Geo1

Geo2

Geo5

Geo10

UnperturbedSAGE1.8_1

Pina7Pina13

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Risks of Climate EngineeringGabriele 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 ….”

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The ROYAL SOCIETY

Strictly Embargoed Until 1st September 2009 11.30 BST

 Stop emitting CO2 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.

GeoengineeringTHE GEOENGINEERING DILEMMA: TO SPEAK OR NOT TO SPEAK?

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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 toguide research and development in the short term, and

possibledeployment 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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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?

GeoengineeringTHE GEOENGINEERING DILEMMA: TO SPEAK OR NOT TO SPEAK?

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GeoengineeringTHE 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.

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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.

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SPARC – Where do we go from here?

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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 thisissue- 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....

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Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000)

Geoengineering Cost Technical Risk of side Nontechnical method $/tC uncertainties effects issues

Injection of CO2 50-150 Less uncertainty Low risk Geoengineering or abate- underground than oceanic storage ment? Possibility of leakage?

Injection of CO2 50-150 Some uncertainty Low risk. Damage to Legal and political concerns: into the ocean about fate of CO2 benthic ecosystem? London Dumping Convention

Intensive forestry, 10-100 Uncertain rate Low risk. Impact on Political questions: how to harvested trees of C capture soil and biodiversity? divide costs? Whose land?

Ocean fertilization 3-10 Can ecosystem alter Moderate risk. O2 Legal concerns: Law of the with phosphate or P:N utilization ratio? depletion? Biota Sea, Antarctic Treaty. iron Long-term capture? change? CH4 release? Effects on fishery?

Space-borne 0.05-0.5 Uncertain costs and Low risk. Security, equity and liability solar shields technical feasibility Albedo CO2 if used for weather control

Stratospheric SO2 : << 1 Uncertain lifetime High risk. Effect on O3. Liability: ozone destruction direct light scattering of aerosols Albedo CO2

Tropospheric aerosol: < 1 Problem of aerosol Moderate risk. Unin- Liability and sovereignty direct light scattering transport and tentional in progress. because aerosol distribution and cloud reflectivity changed cloudiness Albedo CO2 affects regional climate

Emission abatement 100-500 > 50 % abatement No climate risk Who starts? Kyoto problem

Business as usual 10-350 Costs uncertain, Treat risk explicitly, In many sectors social costsStern Rev. 300 $/tC low-prob/hi-impact? higher than marginal costs

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Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000)

Geoengineering Cost Technical Risk of side Nontechnical method $/tC uncertainties effects issues

Injection of CO2 50-150 Less uncertainty Low risk Geoengineering or abate- underground than oceanic storage ment? Possibility of leakage?

Injection of CO2 50-150 Some uncertainty Low risk. Damage to Legal and political concerns: into the ocean about fate of CO2 benthic ecosystem? London Dumping Convention

Intensive forestry, 10-100 Uncertain rate Low risk. Impact on Political questions: how to harvested trees of C capture soil and biodiversity? divide costs? Whose land?

Ocean fertilization 3-10 Can ecosystem alter Moderate risk. O2 Legal concerns: Law of the with phosphate or P:N utilization ratio? depletion? Biota Sea, Antarctic Treaty. iron Long-term capture? change? CH4 release? Effects on fishery?

Space-borne 0.05-0.5 Uncertain costs and Low risk. Security, equity and liability solar shields technical feasibility Albedo CO2 if used for weather control

Stratospheric SO2 : << 1 Uncertain lifetime High risk. Effect on O3. Liability: ozone destruction direct light scattering of aerosols Albedo CO2

Tropospheric aerosol: < 1 Problem of aerosol Moderate risk. Unin- Liability and sovereignty direct light scattering transport and tentional in progress. because aerosol distribution and cloud reflectivity changed cloudiness Albedo CO2 affects regional climate

Emission abatement 100-500 > 50 % abatement No climate risk Who starts? Kyoto problem

Business as usual 10-350 Costs uncertain, Treat risk explicitly, In many sectors social costsStern Rev. 300 $/tC low-prob/hi-impact? higher than marginal costs

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Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000)

Geoengineering Cost Technical Risk of side Nontechnical method $/tC uncertainties effects issues

Injection of CO2 50-150 Less uncertainty Low risk Geoengineering or abate- underground than oceanic storage ment? Possibility of leakage?

Injection of CO2 50-150 Some uncertainty Low risk. Damage to Legal and political concerns: into the ocean about fate of CO2 benthic ecosystem? London Dumping Convention

Intensive forestry, 10-100 Uncertain rate Low risk. Impact on Political questions: how to harvested trees of C capture soil and biodiversity? divide costs? Whose land?

Ocean fertilization 3-10 Can ecosystem alter Moderate risk. O2 Legal concerns: Law of the with phosphate or P:N utilization ratio? depletion? Biota Sea, Antarctic Treaty. iron Long-term capture? change? CH4 release? Effects on fishery?

Space-borne 0.05-0.5 Uncertain costs and Low risk. Security, equity and liability solar shields technical feasibility Albedo CO2 if used for weather control

Stratospheric SO2 : << 1 Uncertain lifetime High risk. Effect on O3. Liability: ozone destruction direct light scattering of aerosols Albedo CO2

Tropospheric aerosol: < 1 Problem of aerosol Moderate risk. Unin- Liability and sovereignty direct light scattering transport and tentional in progress. because aerosol distribution and cloud reflectivity changed cloudiness Albedo CO2 affects regional climate

Emission abatement 100-500 > 50 % abatement No climate risk Who starts? Kyoto problem

Business as usual 10-350 Costs uncertain, Treat risk explicitly, In many sectors social costsStern Rev. 300 $/tC low-prob/hi-impact? higher than marginal costs

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Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000)

Geoengineering Cost Technical Risk of side Nontechnical method $/tC uncertainties effects issues

Injection of CO2 50-150 Less uncertainty Low risk Geoengineering or abate- underground than oceanic storage ment? Possibility of leakage?

Injection of CO2 50-150 Some uncertainty Low risk. Damage to Legal and political concerns: into the ocean about fate of CO2 benthic ecosystem? London Dumping Convention

Intensive forestry, 10-100 Uncertain rate Low risk. Impact on Political questions: how to harvested trees of C capture soil and biodiversity? divide costs? Whose land?

Ocean fertilization 3-10 Can ecosystem alter Moderate risk. O2 Legal concerns: Law of the with phosphate or P:N utilization ratio? depletion? Biota Sea, Antarctic Treaty. iron Long-term capture? change? CH4 release? Effects on fishery?

Space-borne 0.05-0.5 Uncertain costs and Low risk. Security, equity and liability solar shields technical feasibility Albedo CO2 if used for weather control

Stratospheric SO2 : << 1 Uncertain lifetime High risk. Effect on O3. Liability: ozone destruction direct light scattering of aerosols Albedo CO2

Tropospheric aerosol: < 1 Problem of aerosol Moderate risk. Unin- Liability and sovereignty direct light scattering transport and tentional in progress. because aerosol distribution and cloud reflectivity changed cloudiness Albedo CO2 affects regional climate

Emission abatement 100-500 > 50 % abatement No climate risk Who starts? Kyoto problem

Business as usual 10-350 Costs uncertain, Treat risk explicitly, In many sectors social costsStern Rev. 300 $/tC low-prob/hi-impact? higher than marginal costs