Assessment for Decision-Makers Scientiic Assessment of Ozone Depletion: 2014 World Meteorological Organization United Nations Environment Programme National Oceanic and Atmospheric Administration National Aeronautics and Space Administration European Commission Nathalie Huret, Bernard Legras To cite this version: Nathalie Huret, Bernard Legras. Assessment for Decision-Makers Scientiic Assessment of Ozone De- pletion: 2014 World Meteorological Organization United Nations Environment Programme National Oceanic and Atmospheric Administration National Aeronautics and Space Administration European Commission. [Research Report] 56, Assessment for Decision-Makers WMO Global Ozone Research and Monitoring Project – Report No. 56 Scientic Assessment of Ozone Depletion: 2014. 2014, 92 p. insu-01130275 HAL Id: insu-01130275 https://hal-insu.archives-ouvertes.fr/insu-01130275 Submitted on 11 Mar 2015 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Assessment for Decision-Makers Scientic Assessment of Ozone Depletion: 2014 WMO Global Ozone Research and Monitoring Project – Report No. 56 World Meteorological Organization United Nations Environment Programme National Oceanic and Atmospheric Administration National Aeronautics and Space Administration European Commission World Meteorological Organization 7bis, avenue de la Paix Case postale 2300 CH-1211, Geneva 2 Switzerland United Nations Environment Programme Ozone Secretariat P.O. Box 30552 Nairobi, 00100 Kenya U.S. Department of Commerce National Oceanic and Atmospheric Administration 14th Street and Constitution Avenue NW Herbert C. Hoover Building, Room 5128 Washington, D.C. 20230 National Aeronautics and Space Administration Earth Science Division NASA Headquarters 300 E Street SW Washington, D.C. 20546-0001 European Commission Directorate-General for Research and Innovation B-1049 Bruxelles Belgium Published online September 2014 Published in print December 2014 ISBN: 978-9966-076-00-7 Hardcopies of this report are available from WMO (address above; [email protected]). This report and other components of the 2014 Ozone Assessment are available at the following locations: http://www.wmo.int/pages/prog/arep/gaw/ozone_2014/ozone_asst_report.html http://ozone.unep.org/en/assessment_panels_bodies.php?committee_id=7 http://ozone.unep.org/Assessment_Panels/SAP/SAP2014_Assessment_for_Decision-Makers.pdf http://esrl.noaa.gov/csd/assessments/ozone/ Note: Figures from this report are in the public domain and may be used with proper attribution to source. This document should be cited as: WMO (World Meteorological Organization), Assessment for Decision-Makers: Scientific Assessment of Ozone Depletion: 2014, 88 pp., Global Ozone Research and Monitoring Project—Report No. 56, Geneva, Switzerland, 2014. Cover design: Christine A. Ennis, Debra A. Dailey-Fisher, and Albert Romero Cover photo adapted from: ©iStock.com/sharply_done World Meteorological Organization Global Ozone Research and Monitoring Project—Report No. 56 Assessment for Decision-Makers Scientific Assessment of Ozone Depletion: 2014 National Oceanic and Atmospheric Administration National Aeronautics and Space Administration United Nations Environment Programme World Meteorological Organization European Commission Executive Summary Actions taken under the Montreal Protocol have led to decreases in the atmospheric abundance of controlled ozone-depleting substances (ODSs), and are enabling the return of the ozone layer toward 1980 levels. • The sum of the measured tropospheric abundances of substances controlled under the Montreal Protocol continues to decrease. Most of the major controlled ODSs are decreasing largely as projected, and hydrochlorofluorocarbons (HCFCs) and halon-1301 are still increasing. Unknown or unreported sources of carbon tetrachloride are needed to explain its abundance. • Measured stratospheric abundances of chlorine- and bromine-containing substances originating from the degradation of ODSs are decreasing. By 2012, combined chlorine and bromine levels (as estimated by Equivalent Effective Stratospheric Chlorine, EESC) had declined by about 10–15% from the peak values of ten to fifteen years ago. Decreases in atmospheric abundances of methyl chloroform (CH3CCl3), methyl bromide (CH3Br), and chlorofluorocarbons (CFCs) contributed approximately equally to these reductions. • Total column ozone declined over most of the globe during the 1980s and early 1990s (by about 2.5% averaged over 60°S to 60°N). It has remained relatively unchanged since 2000, with indications of a small increase in total column ozone in recent years, as expected. In the upper stratosphere there is a clear recent ozone increase, which climate models suggest can be explained by comparable contributions from declining ODS abundances and upper stratospheric cooling caused by carbon dioxide increases. • The Antarctic ozone hole continues to occur each spring, as expected for the current ODS abundances. The Arctic stratosphere in winter/spring 2011 was particularly cold, which led to large ozone depletion as expected under these conditions. • Total column ozone will recover toward the 1980 benchmark levels over most of the globe under full compliance with the Montreal Protocol. This recovery is expected to occur before midcentury in midlatitudes and the Arctic, and somewhat later for the Antarctic ozone hole. The Antarctic ozone hole has caused significant changes in Southern Hemisphere surface climate in the summer. • Antarctic lower stratospheric cooling due to ozone depletion is very likely the dominant cause of observed changes in Southern Hemisphere tropospheric summertime circulation over recent decades, with associated impacts on surface temperature, precipitation, and the oceans. In the Northern Hemisphere, no robust link has been found between stratospheric ozone depletion and tropospheric climate. Changes in CO2 , N2O, and CH4 will have an increasing influence on the ozone layer as ODSs decline. • As controlled ozone-depleting substances decline, the evolution of the ozone layer in the second half of the st 21 century will largely depend on the atmospheric abundances of CO2, N2O, and CH4. Overall, increasing carbon dioxide (CO2 ) and methane (CH4 ) elevate global ozone, while increasing nitrous oxide (N2O) further depletes global ozone. The Antarctic ozone hole is less sensitive to CO2, N2O, and CH4 abundances. • In the tropics, significant decreases in column ozone are projected during the 21st century. Tropical ozone levels are only weakly affected by ODS decline; they are sensitive to circulation changes driven by CO2 , N2O, and CH4 increases. The climate benefits of the Montreal Protocol could be significantly offset by projected emissions of HFCs used to replace ODSs. The Montreal Protocol and its Amendments and adjustments have made large contributions toward reducing global greenhouse gas emissions. In 2010, the decrease of annual ODS emissions under the Montreal Protocol is estimated to be about 10 gigatonnes of avoided CO2-equivalent emissions per year, which is about five times larger than the annual emissions reduction target for the first commitment period (2008–2012) of the Kyoto Protocol (from the Executive Summary of the Scientific Assessment of Ozone Depletion: 2010).1 1 GWP-weighted emissions, also known as CO2-equivalent emissions, are defined as the amount of gas emitted multiplied by its 100-year Global Warming Potential (GWP). Part of the effect of ODSs as greenhouse gases is offset by the cooling due to changes in ozone. ES-1 • The sum of the hydrofluorocarbons (HFCs) currently used as ODS replacements makes a small contribution of about 0.5 gigatonnes CO2-equivalent emissions per year. These emissions are currently growing at a rate of about 7% per year and are projected to continue to grow. • If the current mix of these substances is unchanged, increasing demand could result in HFC emissions of up to 8.8 gigatonnes CO2-equivalent per year by 2050, nearly as high as the peak emission of CFCs of about 9.5 gigatonnes CO2- equivalent per year in the late 1980s.2 • Replacements of the current mix of high-Global Warming Potential (GWP) HFCs with low-GWP compounds or not-in- kind technologies would essentially avoid these CO2-equivalent emissions. • Some of these candidate low-GWP compounds are hydrofluoro-olefins (HFOs), one of which (HFO-1234yf) yields the persistent degradation product trifluoroacetic acid (TFA) upon atmospheric oxidation. While the environmental effects of TFA are considered to be negligible over the next few decades, potential longer-term impacts could require future evaluations due to the environmental persistence of TFA and uncertainty in future uses of HFOs. • By 2050, HFC banks are estimated to grow to as much as 65 gigatonnes CO2-equivalent. The climate change impact of the HFC banks could be reduced by limiting future use of high-GWP HFCs to avoid the accumulation of the bank, or by destruction of the banks. Additional important issues relevant to the Parties to the Montreal Protocol and other decision-makers