Download 1650_Velders_ODSuncertainties

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Uncertainties in
projections of ozonedepleting substances
and alternatives
Guus Velders
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May 14, 2014
Focus on Ozone-Depleting Substances
● Projections of gases controlled by the Montreal Protocol
– CFCs, halons, HCFCs, carbon tetrachloride, methyl chloroform, CH3Br
● Projections for WMO assessments:
– Made by 2D and 3D models
– Policy options/scenarios often with box model
● Equivalent Effective Stratospheric Chlorine
(EESC)
– Index for stratospheric chlorine and
bromine and their ability to destroy ozone
– Uncertainties mostly not taken into account
● Uncertainties are important for these
projections
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Comprehensive uncertainty analyses
● EESC calculation using baseline production of ODSs from WMO(2011)
● Same box model as in WMO(2011) used
● Uncertainties applied to
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Lifetimes of all ODSs from SPARC (2013):
Production (past from UNEP) and future:
Banks from TEAP:
Emission factors:
Fractional release values:
Alpha (efficiency of Br compared to Cl):
Age-of-air (vertical transport):
Observed mixing ratios (as constraint):
Surface factor:
1σ
.
12-33%
5%
10%, 20%
10%, 20%
10%, 20%
25%
0.3 yr
0.1 ppt
3%
 Monte Carlo uncertainty analysis
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Range in future mixing ratios
● Lifetimes and uncertainties from SPARC (2013)
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Most likely and possible uncertainty ranges (1σ)
CFC-11:
52 yr 11% or 22%
CFC-12:
102 yr 8% or 15%
HCFC-22:
12 yr 16%
Halon-1211: 16 yr 33%
Halon-1301: 72 yr 9% or 13%
● Data before 2010 constrained by
observations
● Mixing ratio range (95% conf.) 2050
– ±35 ppt for CFC-11
– ±48 ppt for CFC-12
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Range in future EESC levels
● Uncertainties applied to lifetimes (of all ODSs) only
● EESC (mixing ratios) before 2010 constraint by observations
● Range in EESC levels
– Mean: 1200 ppt in 2050
– Range 1050-1350 ppt
● EESC return to 1980 levels
– Mid-latitudes: 2048
● Range 2040 to 2061
– Antarctic:
2075
● Range 2062 to 2101
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ODSs contributing most to EESC uncertainty
● EESC return to pre-1980 levels
● Largest contributions from CFC-11
and Halon-1211
● Correlations between uncertainties
taken into account:
CFCs, CCl4, Halon-1301:
– Species mainly removed by
photolysis in stratosphere
HCFCs, methyl chloroform, Halon1211, CH3Cl, CH3Br:
– Species mainly removed by OH in
troposphere
● Correlations increase total
uncertainty
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Range in future EESC levels: all uncertainties
● Uncertainties applied to all parameters
and all ODSs
● EESC return to 1980 levels
– Mid-latitudes: 2048
● Range 2039 to 2064
– Antarctic:
2075
● Range 2061 to 2105
● Ranges only slightly larger than with
uncertainties in lifetimes only
● Lower range: equal to zero
emissions scenario
● Upper range: 12 times total projected
HCFC emissions (2014-2050)
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Parameters contributing most to EESC uncertainty
● Uncertainties applied to all parameters
● Ranges in year of return to pre-1980
levels
● Largest contributions
– Uncertainties in lifetimes
● Other contributions from
– Age-of-air
– Fractional release values
– Bromine efficiency (alpha)
● Atmospheric burden much
larger than current banks
– Factor of 4 for CFC-11
– Factor of 30 for CFC-12
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Uncertainties in ODP-weighted emissions
● ODPs also have uncertainties
– CFCs: 30-35%
– HCFCs: 55-70%
– Halons: 60-90%
● Large contributions again from
uncertainties in lifetimes
● Peak emission
– Mean: 1.3 MtCFC-11-eq/yr
– Range 0.9 to 1.8 MtCFC-11-eq/yr
● Total uncertainties (95% conf.)
of 20% to more than 40%
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Other factors also affect future ozone layer
● Non-Montreal Protocol related changes also important
● Increases in other gases: CO2, CH4, N2O:
– Changes through chemical reactions: HOx, HCl, NOx, ClONO2
– Changes through temperature and dynamics of the atmosphere
● Changes in emissions of very short lives species (VSLS)
● Also potential effects from:
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Rockets
Aircraft
Volcanoes
Geoengineering
Biofuels
etc.
Mt Pinatubo
Picture NOAA/ESRL
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Uncertainties in GWP-weighted emissions and RF
● Uncertainties can also be translated to climate metrics: GWP and RF
● Additional uncertainties from radiative efficiency and CO2 forcing
● Uncertainties: 20-40%
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Uncertainties in scenarios of ODS alternatives
● Alternatives used for ozone-depleting
substances
– Hydrocarbons, CO2, NH3
– Alternative technologies: Mineral wool, etc.
– HFCs with long lifetimes:
HFC-134a, HFC-125, HFC-143a, etc.
– HFCs with short lifetimes:
HFC-1234yf, HFC-1234ze, etc.
● Uncertainties in HFCs lifetimes ~20%
● Scenario uncertainty more important
● If current HFC mix (lifetime 15 yr) were
replaced by HFCs with lifetimes less 1 month 
forcing in 2050 less than current HFC forcing
Velders et al. Science (2012)
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Changes in types of applications: CFCs vs HFCs
● CFCs (1980s) used in very emissive applications
– Spray cans, chemical cleaning
– Release within a year
● HFCs used mostly in slow release applications
– Refrigeration, AC: release from 1 – 10 yr
– Foams: release > 10 yr
Velders et al. (20124)
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Role of the banks increases for HFCs
● Banks: HFCs present in equipment:
refrigerators, AC, foams, etc.
● Bank about 7 times annual emission
● Phaseout in 2020 instead of 2050
– Avoided emission: 91-146 GtCO2-eq
– Avoided bank:
39- 64 GtCO2-eq
 Banks: climate change commitment
● Choices:
– Bank collection, destruction: difficult/costly
– Avoid the buildup of the bank: early
phaseout
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Conclusions
● Uncertainties in lifetimes most important for EESC projections
– Scenario uncertainty more important for ODS alternatives
● Growing importance of HFC banks for climate change
Work performed in close collaboration with
John Daniel (NOAA, USA)
Thank you for
your attention
References:
- Velders and Daniel, Atmos. Chem. Phys., 2014
- Velders, Solomon and Danel, Atmos. Chem. Phys., 2014
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