Microphysics of PSCs: modelling and lidar observations

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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 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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Geoengineering THE GEOENGINEERING DILEMMA TO
SPEAK OR NOT TO SPEAK?

• 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

Morton, Nature 2007
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

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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 612 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
Geo0 Geo1 Geo2 Geo5 Geo10 Pina10
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Nonlinear injection-burden 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.

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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 loss
• Close investigation required.

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Impact on ozone layer
Change in total ozone column

• 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

Geo5 Geo5 no radiation Geo5 no chemistry
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
Unperturbed SAGE1.8_1 Pina7 Pina13
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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 .
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.
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Geoengineering THE GEOENGINEERING DILEMMA TO
SPEAK OR NOT TO SPEAK?
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.
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• Key recommendations on geoengineering
• 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
• 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
• 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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Geoengineering THE GEOENGINEERING DILEMMA TO
SPEAK OR NOT TO SPEAK?

• Ethical caveats remain!
• They call for not applying geoengineering, maybe
  even for not doing exploratory research on
  geoengineering. How serious are they?
• The scientific thought process cannot not be
  reversed, not even be stopped!
• Global warming was unintentional. But is todays
  continuation of it still unintentional? Or
  just unavoidable? Or not even this, rather
  just common practice?
• Could a united opinion of scientists worldwide
  keep us all from abusing geoengineering or is
  this just a naïve conception?

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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 cant 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 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....
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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 PN
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 ltlt 1 Uncertain lifetime
High risk. Effect on O3. Liability ozone
destruction direct light scattering of
aerosols Albedo ? ? CO2 ? Tropospheric
aerosol lt 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 gt 50 abatement No climate
risk Who starts? Kyoto problem Business as
usual 10-350 Costs uncertain, Treat risk
explicitly, In many sectors social
costs Stern Rev. 300 /tC low-prob/hi-impact?
higher than marginal costs
CO2 abatement
CO2 engineering
Albedo engineering
19
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 PN
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 ltlt 1 Uncertain lifetime
High risk. Effect on O3. Liability ozone
destruction direct light scattering of
aerosols Albedo ? ? CO2 ? Tropospheric
aerosol lt 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 gt 50 abatement No climate
risk Who starts? Kyoto problem Business as
usual 10-350 Costs uncertain, Treat risk
explicitly, In many sectors social
costs Stern Rev. 300 /tC low-prob/hi-impact?
higher than marginal costs
CO2 abatement
CO2 engineering
Albedo engineering
20
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 PN
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 ltlt 1 Uncertain lifetime
High risk. Effect on O3. Liability ozone
destruction direct light scattering of
aerosols Albedo ? ? CO2 ? Tropospheric
aerosol lt 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 gt 50 abatement No climate
risk Who starts? Kyoto problem Business as
usual 10-350 Costs uncertain, Treat risk
explicitly, In many sectors social
costs Stern Rev. 300 /tC low-prob/hi-impact?
higher than marginal costs
CO2 abatement
CO2 engineering
Albedo engineering
21
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 PN
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 ltlt 1 Uncertain lifetime
High risk. Effect on O3. Liability ozone
destruction direct light scattering of
aerosols Albedo ? ? CO2 ? Tropospheric
aerosol lt 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 gt 50 abatement No climate
risk Who starts? Kyoto problem Business as
usual 10-350 Costs uncertain, Treat risk
explicitly, In many sectors social
costs Stern Rev. 300 /tC low-prob/hi-impact?
higher than marginal costs
CO2 abatement
CO2 engineering
Albedo engineering