Transcript Microphysics of PSCs: modelling and lidar observations

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 greenhouse 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)
5.3 Tg S stratospheric burden
needed to compensate 4 W/m2 RF
expected from CO2 doubling
[Crutzen, 2006]
[Crutzen and Ramanathan, 2003]
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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 geoengineering
Use AER 2D aerosol model input to CCM SOCOL
Volcanic eruption:
1 single SO2 injection
Pina10: 10 Mt S in June 1991
7 Mt S in January 1992
Geoengineering:
continuous SO2 emissions
Formation of larger
aerosol particles
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
no sedimentation
Rasch et al.,
GRL 2008
coag/10
2x/yr
• 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
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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
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Impact on ozone layer
Change in total ozone column
Geo5
Geo5 no radiation
Geo5 no chemistry
Scenario name

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
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
Geo1
Geo2
Geo5
Geo10
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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:
(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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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?
(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?
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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 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 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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Albedo engineering
CO2 engineering CO2 abatement
Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000)
Geoengineering
method
Cost
$/tC
Injection of CO2
underground
50-150 Less uncertainty
Low risk
than oceanic storage
Geoengineering or abatement? Possibility of leakage?
Injection of CO2
into the ocean
50-150 Some uncertainty
about fate of CO2
Low risk. Damage to
benthic ecosystem?
Legal and political concerns:
London Dumping Convention
Intensive forestry,
harvested trees
10-100 Uncertain rate
of C capture
Low risk. Impact on Political questions: how to
soil and biodiversity? divide costs? Whose land?
Ocean fertilization
with phosphate or
iron
3-10
Space-borne
solar shields
0.05-0.5 Uncertain costs and Low risk.
technical feasibility Albedo   CO2 
Stratospheric SO2 :
<< 1
direct light scattering
Tropospheric aerosol:
sovereignty
direct light scattering
and cloud reflectivity
climate
Technical
uncertainties
Risk of side
effects
Nontechnical
issues
Can ecosystem alter Moderate risk. O2
Legal concerns: Law of the
P:N utilization ratio? depletion? Biota
Sea, Antarctic Treaty.
Long-term capture? change? CH4 release? Effects on fishery?
Security, equity and liability
if used for weather control
Uncertain lifetime
High risk. Effect on O3. Liability: ozone destruction
of aerosols
Albedo   CO2 
<1
Problem of aerosol
Moderate risk. Unin- Liability and
transport and
tentional in progress. because aerosol distribution
changed cloudiness Albedo   CO2 
affects regional
Emission abatement 100-500 > 50 % abatement
No climate risk
Who starts? Kyoto problem
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Albedo engineering
CO2 engineering CO2 abatement
Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000)
Geoengineering
method
Cost
$/tC
Injection of CO2
underground
50-150 Less uncertainty
Low risk
than oceanic storage
Geoengineering or abatement? Possibility of leakage?
Injection of CO2
into the ocean
50-150 Some uncertainty
about fate of CO2
Low risk. Damage to
benthic ecosystem?
Legal and political concerns:
London Dumping Convention
Intensive forestry,
harvested trees
10-100 Uncertain rate
of C capture
Low risk. Impact on Political questions: how to
soil and biodiversity? divide costs? Whose land?
Ocean fertilization
with phosphate or
iron
3-10
Space-borne
solar shields
0.05-0.5 Uncertain costs and Low risk.
technical feasibility Albedo   CO2 
Stratospheric SO2 :
<< 1
direct light scattering
Tropospheric aerosol:
sovereignty
direct light scattering
and cloud reflectivity
climate
Technical
uncertainties
Risk of side
effects
Nontechnical
issues
Can ecosystem alter Moderate risk. O2
Legal concerns: Law of the
P:N utilization ratio? depletion? Biota
Sea, Antarctic Treaty.
Long-term capture? change? CH4 release? Effects on fishery?
Security, equity and liability
if used for weather control
Uncertain lifetime
High risk. Effect on O3. Liability: ozone destruction
of aerosols
Albedo   CO2 
<1
Problem of aerosol
Moderate risk. Unin- Liability and
transport and
tentional in progress. because aerosol distribution
changed cloudiness Albedo   CO2 
affects regional
Emission abatement 100-500 > 50 % abatement
No climate risk
Who starts? Kyoto problem
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Albedo engineering
CO2 engineering CO2 abatement
Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000)
Geoengineering
method
Cost
$/tC
Injection of CO2
underground
50-150 Less uncertainty
Low risk
than oceanic storage
Geoengineering or abatement? Possibility of leakage?
Injection of CO2
into the ocean
50-150 Some uncertainty
about fate of CO2
Low risk. Damage to
benthic ecosystem?
Legal and political concerns:
London Dumping Convention
Intensive forestry,
harvested trees
10-100 Uncertain rate
of C capture
Low risk. Impact on Political questions: how to
soil and biodiversity? divide costs? Whose land?
Ocean fertilization
with phosphate or
iron
3-10
Space-borne
solar shields
0.05-0.5 Uncertain costs and Low risk.
technical feasibility Albedo   CO2 
Stratospheric SO2 :
<< 1
direct light scattering
Tropospheric aerosol:
sovereignty
direct light scattering
and cloud reflectivity
climate
Technical
uncertainties
Risk of side
effects
Nontechnical
issues
Can ecosystem alter Moderate risk. O2
Legal concerns: Law of the
P:N utilization ratio? depletion? Biota
Sea, Antarctic Treaty.
Long-term capture? change? CH4 release? Effects on fishery?
Security, equity and liability
if used for weather control
Uncertain lifetime
High risk. Effect on O3. Liability: ozone destruction
of aerosols
Albedo   CO2 
<1
Problem of aerosol
Moderate risk. Unin- Liability and
transport and
tentional in progress. because aerosol distribution
changed cloudiness Albedo   CO2 
affects regional
Emission abatement 100-500 > 50 % abatement
No climate risk
Who starts? Kyoto problem
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Albedo engineering
CO2 engineering CO2 abatement
Comparison of geoengineering options (adapted from D.W. Keith, Annu. Rev. Energy Environ., 2000)
Geoengineering
method
Cost
$/tC
Injection of CO2
underground
50-150 Less uncertainty
Low risk
than oceanic storage
Geoengineering or abatement? Possibility of leakage?
Injection of CO2
into the ocean
50-150 Some uncertainty
about fate of CO2
Low risk. Damage to
benthic ecosystem?
Legal and political concerns:
London Dumping Convention
Intensive forestry,
harvested trees
10-100 Uncertain rate
of C capture
Low risk. Impact on Political questions: how to
soil and biodiversity? divide costs? Whose land?
Ocean fertilization
with phosphate or
iron
3-10
Space-borne
solar shields
0.05-0.5 Uncertain costs and Low risk.
technical feasibility Albedo   CO2 
Stratospheric SO2 :
<< 1
direct light scattering
Tropospheric aerosol:
sovereignty
direct light scattering
and cloud reflectivity
climate
Technical
uncertainties
Risk of side
effects
Nontechnical
issues
Can ecosystem alter Moderate risk. O2
Legal concerns: Law of the
P:N utilization ratio? depletion? Biota
Sea, Antarctic Treaty.
Long-term capture? change? CH4 release? Effects on fishery?
Security, equity and liability
if used for weather control
Uncertain lifetime
High risk. Effect on O3. Liability: ozone destruction
of aerosols
Albedo   CO2 
<1
Problem of aerosol
Moderate risk. Unin- Liability and
transport and
tentional in progress. because aerosol distribution
changed cloudiness Albedo   CO2 
affects regional
Emission abatement 100-500 > 50 % abatement
No climate risk
Who starts? Kyoto problem
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