Estimated HCFC emissions for — in China and the increasing contribution to global emissions. Vollmer, M. Emissions of ozone-depleting halocarbons from China. Rosenlof, K. Trends in the temperature and water vapor content of the tropical lower stratosphere: sea surface connection. ADS Google Scholar. On the structural changes in the Brewer—Dobson circulation after Download references. We thank R. Wang for algorithms for extracting background mole fractions from those influenced by recent emission input, and for calculating correlations between CFC data from the American Samoa and Barbados stations and ENSO, and M.
Lickley for discussions and results from Bayesian banks analysis. Stephen A. Montzka, Geoffrey S. Dutton, Bradley D. Hall, Carolina Siso, J. Geoffrey S. David Nance. Salameh, Christina M. You can also search for this author in PubMed Google Scholar. Correspondence to Stephen A. Peer review information Nature thanks Martin Dameris, Ross Salawitch and the other, anonymous, reviewer s for their contribution to the peer review of this work. Peer reviewer reports are available.
Monthly measured mean mole fractions and standard deviations at 5 remote sites Extended Data Table 1. Hemispheric annual means centred on 1 January of year given Northern Hemisphere, red circles; Southern Hemisphere, blue circles are derived from results at these 5 sites Methods. Each point represents a flask pair mean from all flasks sampled during autumn of the indicated year fraction of year 0. The linear regression coefficients r 2 and slopes of these lines are plotted in Fig.
Results in and most earlier years show a high correlation for these two gases, which are emitted in substantial quantities from eastern Asian countries 39 , These results and transport modelling Extended Data Fig. Three surface sensitivities were calculated with the NAME model 19 for a number of regions bordering the Pacific Ocean basin during each of the three hours surrounding a sampling event Methods. These surface sensitivities are the time integrated air concentration simulated within the surface layer 0—2, m over this region during the 30 days before each sampling event given a point release at MLO of 1 g h —1.
Measured flask pair mean mole fractions red symbols and lines, right-hand y -axis; uncertainties represent 1 s. Correlation coefficients r are given in parentheses.
This indicates that wind patterns consistently transported Asian-influenced air to MLO in autumn of all these years. Enhancements of CFC in samples having enhanced surface sensitivity to eastern China and neighbouring regions, however, are observed only in and By CFC enhancements are no longer measureable above instrumental noise about 0.
Results indicate that for all methods of estimation, the general pattern of emission changes over the past decade is robust, including the substantially reduced emissions in While year-to-year changes estimated from remote-atmosphere observations with 3- or box models are typically within 1-s. For emissions derived with the box model a and b , emissions were inferred in each semi-hemisphere and season with a least-squares approach, and subsequently were summed to global annual means 1 , 3.
The results suggest that much of this observed variability is not measurement noise or inaccuracies in maintaining calibration consistency, but instead reflects real variability in dynamics that is captured in these 3D model simulations. Measured variability not reproduced by the 3D models could represent the influence of short-term changes in emissions not captured by the smoothly varying emission input or measurement errors.
The variations in derived rates in the two hemispheres most often co-vary, suggesting that this variability is associated with vertical exchange between the troposphere and stratosphere or stratospheric dynamics such as the quasi-biennial oscillation 20 as opposed to variations in tropospheric exchange between the hemispheres.
For calendar year mean values derived from the two models, the difference in the magnitude of bias estimated from these two 3D models since is 3. The bias-corrected results indicate that dynamics accelerated the decline in CFC mole fractions and global emission after , implying that the emission decrease from to is overestimated by up to 4 Gg yr —1 without consideration of variable dynamics.
The shift to negative bias following that persisted until and is captured by both models is a result of a known perturbation to stratospheric circulation 24 , 41 , Excess global emissions are derived from the difference between measurement-derived emissions NOAA and AGAGE combined estimate, corrected for dynamics and the emission expectations considering no post production that are shown in Fig.
Expectations are derived from: 1 an extrapolated linear fit to observationally derived emissions during to red solid line, uncertainties represent 1 s. For clarity, quantitative estimates of excess emission from these data are tabulated below the chart for different periods, and some of these values are quoted in the main text. While global excess emissions have substantial uncertainties, the results from eastern China suggests that this region accounted for a larger fraction of the global excess emission before than after it.
Larger excess emissions in may suggest substantially larger increases in the CFC foam bank from recent production, but also could reflect continued emissions from ongoing production and foam manufacturing.
For reference, reported total global production of CFC peaked in the late s at Gg yr —1 and in the Article 5 Parties to the Montreal Protocol developing countries it peaked in at 47 kt yr —1 ref. These emissions were calculated with a CFC lifetime of yr ref. As a result, differences in results from the two measurement networks probably reflect errors in instrument operations or standardization over time.
Substantial co-production and emission of CFC would imply larger impacts of the renewed CFC production on future stratospheric ozone than are derived from the consideration of CFC alone.
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Advanced search. Skip to main content Thank you for visiting nature. Download PDF. Subjects Atmospheric chemistry Atmospheric dynamics Environmental impact. Abstract The atmospheric concentration of trichlorofluoromethane CFC has been in decline since the production of ozone-depleting substances was phased out under the Montreal Protocol 1 , 2. Main After the discovery 1 that global emissions and probably also production of the potent ozone-depleting chemical CFC increased after —despite Montreal Protocol controls banning production by —scientists, industry experts, policy makers and others sought information to enable rapid mitigation and to ensure protection of the ozone layer 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , Full size image.
Hemispheric mole fraction differences Hemispheric concentration differences reflect hemispheric asymmetries in emission magnitudes and loss, and these asymmetries are modulated by interhemispheric transport. Observationally derived global emissions Global CFC emissions were estimated with 3-box and box models to yield tropospheric mole fractions consistent with surface data using established methodologies 1 , 3 with some modifications to enable the consideration of NOAA and AGAGE data together see below.
Estimating dynamical influences Three-dimensional model simulations were used to estimate the influence of dynamics-induced variability on CFC mole fractions and derived emissions.
Expected emissions after Without post production, CFC emissions were expected to slowly decline thereafter as reservoirs of CFC banks , primarily in foam, but also in industrial process refrigeration and comfort cooling for commercial buildings chillers , diminished from the CFC escaping to the atmosphere 4 , 15 , 16 , 17 , 22 , Estimating excess global emissions Excess global emissions emissions above expectations considering only reported production were derived as the difference between observationally based estimates and expected emissions estimated using methods discussed above.
Estimating enhanced production and banks While atmospheric observations provide a straightforward way to derive global emissions, an estimate of production magnitudes and additions to banks that accounts for the emission enhancement requires additional information that was recently reassessed 4.
References 1. Google Scholar 7. CAS Google Scholar ADS Google Scholar Montzka View author publications. View author publications. Ethics declarations Competing interests The authors declare no competing interests.
Additional information Peer review information Nature thanks Martin Dameris, Ross Salawitch and the other, anonymous, reviewer s for their contribution to the peer review of this work. Extended data figures and tables. Extended Data Fig. Extended Data Table 1 Measurement site locations, instrumental methods and associated network Full size table.
Supplementary information Peer Review File. Source data Source Data Fig. Source Data Fig. Rights and permissions Reprints and Permissions. About this article. Cite this article Montzka, S. Hydrofluorocarbons HFCs , which have been used in recent years in increasing quantities as substitutes for CFCs, are also climatically very active and many are also extremely long-lived. In the journal Science an international team of researchers recommends that the most potent of these gases also be regulated.
This could save the positive "side effect" of the Montreal Protocol for the global climate. It is regarded as the most successful international environmental agreement and has, to date, been ratified by countries -- the Montreal Protocol on Substances That Deplete the Ozone Layer. As a result, CFCs and ozone "killers" will gradually disappear from the atmosphere over the coming decades.
And because many of these substances are also very active greenhouse gases, Earth's climate will profit from the sinking concentrations too. So far, so good. In many processes where previously CFCs were used, these are now being increasingly substituted by fluorinated compounds such as HFCs which, simply put, are similar substances to CFCs but do not contain chlorine and do not deplete stratospheric ozone.
They are used as cooling agents in air conditioning plants and refrigerators, as propellants in aerosol cans, as solvents and as foaming agents in the manufacture of foam products. However, there is a downside to the use of HFCs -- they are also very potent greenhouse gases. HFCa, also known as Ra, for example, which is used in automobile air conditioning units, is more active than the "classic" greenhouse gas carbon dioxide CO 2.
The reduction of greenhouse gas emissions is covered by the Kyoto Protocol. This agreement is, however, not binding for the world's largest emitter of greenhouse gases, the USA which has never ratified the protocol , nor for threshold and developing countries. In addition the Kyoto Protocol is currently limited to the period from to No agreement has yet been reached on extending it.
What this means is that the significant increase in global emissions of HFCs seen over the past few years will soon negate the positive effects on climate brought by the Montreal protocol's CFC phase-out. This link is shown by an analysis published in the latest issue of "Science. Since the year the radiative forcing a measure of the effect on the climate of chemical substances of all ozone-depleting substances including CFCs has remained at a more or less constant value of 0.
Had the Montreal Protocol recommendations not been implemented, today's value would be approximately double this figure, i. Measurements of ozone concentration were carried out by instruments carried into the stratosphere by balloons and aircraft. Ozone was also measured by instruments on satellites orbiting Earth, though satellite technology in the mids was still rather primitive. The crucial evidence supporting the CFC hypothesis came from British scientists working at the Halley Bay Station of the British Antarctic Survey, who had been taking ground-based measurements of total ozone for decades.
In , Joseph C. Farman and his colleagues at BAS studied the raw data and found that stratospheric ozone had decreased greatly since the s. The Antarctic ozone hole, as it came to be known, made depletion of the ozone layer a real and present danger to lawmakers and the public at large.
Predictions of significant increases in the incidence of skin cancer resulting from continued use of CFCs spurred international action. In , 56 countries agreed under what became known as the Montreal Protocol to cut CFC production and use in half.
In subsequent years, the protocol was strengthened to require an eventual worldwide phaseout of the production of CFCs and other ozone depleting chemicals. It is a global problem.
What is important is that it led to an international agreement that solved the problem. Their unprecedented advocacy ultimately led to the phasing out of CFCs worldwide through the passage of the Montreal Protocol in The research of Rowland and Molina brought worldwide attention to the impact of human-contributed pollution on a planetary scale.
Their work was among the first to directly effect a global shift in policy, preceding the current debate on climate change. ACS designated F. The commemorative plaque reads:. At the University of California, Irvine, F.
When the scientists reported their findings in , CFCs were widely used as refrigerant gases and as propellants in aerosol sprays. Rowland and Molina convinced skeptical industrialists, policymakers, and the public of the danger of CFCs. Chlorofluorocarbons and Ozone Depletion.
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