2018 WMO/UNEP Assessment Co-chairs:

David Fahey (USA) Paul Newman (USA)

John Pyle (UK) Bonfils Safari (Rwanda)

Assessment Coordinator:

Sarah Doherty (USA)

2014 Assessment

2018 Assessment

The 2018 WMO/UNEP Scientific Assessment of Ozone Depletion

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Scienti'icAssessmentofOzoneDepletion:2018

Steering Committee

Martyn Chipperfield (UK) David Fahey (USA) David Karoly (Australia) Doug Kinnison (USA) Malcolm Ko (USA) Paul Newman (USA) John Pyle (UK) Bonfils Safari (Rwanda) Michelle Santee (USA)

Chapter 1: Ozone-depleting substances Andreas Engel (Goethe Universität Frankfurt, Germany) Matt Rigby (University of Bristol, UK)

Chapter 2: Hydrofluorocarbons Steve Montzka (NOAA, ESRL, USA) Guus Velders (Natl. Inst. for Pub. Health and the Env., Netherlands)

Chapter 3: Global stratospheric ozone: Past, present & future Peter Braesicke (Karlsruhe Institute für Technologie, Germany) Jessica Neu (NASA JPL, USA)

Chapter 4: Polar stratospheric ozone: Past, present & future Ulrike Langematz (Freie Universität Berlin, Germany) Matt Tully (Bureau of Meterology, Australia)

Chapter 5: Stratospheric ozone changes and climate Alexey Karpechko (Finnish Meteorological Institute (Finland) Amanda Maycock (University of Leeds, UK)

Chapter 6: Scenarios and information for policymakers Lucy Carpenter (University of York, UK) John Daniel (NOAA, ESRL, USA)

Chapters and Lead Authors

International assessment process

Assessment report team: •  41 Lead authors and co-authors •  12 Review Editors •  19 Different countries

Peer review process: •  126 Science reviewers •  32 Different countries •  > 5000 Review comments on first draft!

20 Questions and Answers

Twenty Questions and Answers About the Ozone Layer: 2014 UpdateScientific Assessment of Ozone Depletion: 2014

World Meteorological Organization United Nations Environment Programme National Oceanic and Atmospheric Administration National Aeronautics and Space Administration European Commission

The ‘20 Questions’ document is being revised and updated

Assessment highlights: Comprehensive evaluation of metrics

•  A new table with updated evaluation of abundances, lifetimes, ODPs, GWPs and GTPs of more than 500 compounds.

•  CFCs, HCFCs, HFCs, HCs, halogenated ethers, alcohols and ketones, fluoroesters, etc.

•  Metrics for many HCFCs evaluated for the first time (Papanastasiou et al., 2017) providing new information for Group I Annex C table.

• Annex C of the Kigali Amendment includes a table of HCFCs with many missing global warming potential (GWP) values.

• GWPs needed to establish baselines for HFC phase down schedules.

• A new theoretical NOAA study provides estimates of missing GWPs, otherwise assumed zero.

•  Table includes 274 HCFC isomers •  Large range of values - structure dependent

• Detailed laboratory studies could provide more accurate determinations for selected compounds

Assessment highlight: Halogenated Very Short Lived Substances (VSLS)

•  Previous assessments have discussed natural and anthropogenic VSLS - ODS with lifetimes less than about 6 months.

•  Recent interest focuses on chlorinated VSLS, including: CH2Cl2 (dichloromethane, DCM), lifetime ~ 140 days CH2ClCH2Cl (1,2-dichloroethane, DCE), ~ 65 days

•  We estimate VSLS up to ~ 3.3% of lower stratospheric chlorine, with up to ~1.8% from DCM and ~ 0.6% from DCE.

•  Estimates have high uncertainty because of sparse stratospheric observations and variability in VSLS sources.

VSLS, continued FIRST ORDER DRAFT – DO NOT CITE CHAPTER 1: ODSs

OZONE ASSESSMENT 2018: ver.15 Sept 2017 99

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Figure 1-9. Modelled and observed stratospheric chlorine SGI (ppt Cl) from (a) CH2Cl2, (b) 3

CHCl3, (c) C2Cl4, (d) CH2ClCH2Cl and (e) total. Update of Hossaini et al. [2015]. 4

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•  Tropospheric VSLS chlorine concentrations increased from ~85ppt in 2008 to ~110ppt in 2016.

•  Largest increases have occurred for CH2Cl2 (dichloromethane)

•  VSLS chlorine currently makes a very small contribution to stratospheric ozone depletion

•  Understanding the role of VSLS emissions in long-term future stratospheric ozone change remains an open science question.

Assessment highlight: Ozone Recovery

•  Arctic ozone remains below average with expected large depletions occurring every few years (e.g., 2011)

•  Antarctic ozone is well below average with some hints at improvement

2017

•  Small 2017 Antarctic hole mainly due to unusual meteorological conditions

Assessment highlight: HFCs – Kigali amendment

•  Kigali amendment controls HFC emissions and is projected to limit future surface warming from HFCs to less than 0.1C in 2100

•  New chapter on HFCs in the 2018 assessment

FIRST ORDER DRAFT – DO NOT CITE CHAPTER 2: HFCs

OZONE ASSESSMENT 2018: ver.15 Sept 2017 212

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Figure 2-17. Timeseries of the temperature response to HFCs in the 10–16 km layer (K), as 2

compared with 2015 conditions. The gray shading shows the projected contributions due to 3

increasing HFCs under business-as-usual scenarios (Miller and Kuijpers, 2011, Velders et al., 4

2015). The red, green and blue lines, respectively, show the temperature responses for three 5

mitigation scenarios in which HFC emissions initially follow the Velders et al (2015) upper 6

range scenario, then are eliminated beginning in 2020, 2030 or 2040. Figure from Hurwitz et al. 7

(2016). 8

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Figure 2-18. The contribution of HFCs to the average surface warming of the Earth with and 11

without the Kigali amendment. The scenarios without the measures are based on Xu et al. (2013) 12

and Velders et al. (2015) which differ in their assumptions for the projections of the demand for 13

HFCs past 2050. The surface temperature change based on Velders et al. (2015) is calculated 14

using the MAGICC6 model. 15

HFC Emissions

2000 2010 2020 2030 2040 2050Year

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Emiss

ions

(GtC

O2-e

q yr

-1)

GWP-weighted (100-yr)

Baseline Velders (2015)

Kigali Amendment

2018 Assessment Timeline þ  Discussion Paper circulated for comments by scientific community þ  Lead Authors and Chapter Editors established

þ  Chapter author teams assembled, early preparation steps begin þ  Draft of Chapter outlines (31 Mar)

q  Prelim. 2nd draft of Chapters + review responses sent to Rev. Editors (31 Jan)

q  Review meeting of 2nd draft (Boulder, CO, 26-29 March) •  Presentation of Exec. Summ. 1st draft, based on Chapter 2nd drafts •  SSC meets to revise Exec. Summ. the day after the meeting concludes

q  Final versions of Chapters completed (1 June) q  Panel Review Meeting for Exec. Summary (Les Diablerets, 16-20 Jul)

2017

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18 q  2nd draft of Chapters completed (28 Feb)

q  All cited papers accepted for publication (15 May)

þ  1st meeting of Lead Authors, Co-chairs, SSC (4-5 May) þ  Individual Chapter team meeting (May-Jul) þ  Draft chapter summary bullets submitted for review

after chapter-level meetings (~15 Jul) þ  1st drafts of Chapters completed (15 Sep)

•  1st drafts sent to reviewers & Review Editors •  SSC begins writing of Exec. Summary

þ  Chapter 1st draft reviews due (15 Nov) þ  Collated chapter reviews sent to Lead Authors & Review Editors (by 22 Nov)

•  Review Editors provide feedback to Lead Authors on key items from reviews (~1 Dec)

Thank you for your attention