1 May 14, 2014

Uncertainties in projections of ozone-depleting substances and alternatives

Guus Velders

The Netherlands

(RIVM)

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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 1σ . – Lifetimes of all ODSs from SPARC (2013): 12-33%– Production (past from UNEP) and future: 5%– Banks from TEAP: 10%, 20%– Emission factors: 10%, 20%– Fractional release values: 10%, 20%– Alpha (efficiency of Br compared to Cl): 25%– Age-of-air (vertical transport): 0.3 yr– Observed mixing ratios (as constraint): 0.1 ppt– Surface factor: 3%

Monte Carlo uncertainty analysis

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Range in future mixing ratios

● Lifetimes and uncertainties from SPARC (2013)– 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, Halon-1211, 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:

– Rockets– Aircraft– Volcanoes– Geoengineering– Biofuels– etc.

Picture NOAA/ESRL

Mt Pinatubo

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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% 10-30%

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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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● 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 withJohn Daniel (NOAA, USA)

Thank you for your attention

References: - Velders and Daniel, Atmos. Chem. Phys., 2014- Velders, Solomon and Danel, Atmos. Chem. Phys., 2014

Conclusions