Ozone: The Earth's protective shield is repairing. Scientists examine the great 'human pause'. The ozone hole over Antarctica in the year Image source, Getty Images. Ozone: The Earth's protective shield is repairing Covid pandemic has little impact on rise in CO2 Scientists examine the great 'human pause'. This video can not be played To play this video you need to enable JavaScript in your browser. The visualisation from tracked the behaviour of the ozone layer.
Related Topics. 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. Reprints and Permissions. Download citation.
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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.
The uniform mixing of CF4 versus altitude was reported from balloons around and many times since, and from an infrared instrument aboard the space shuttle Challenger which exploded in in We once did a descent directly over the North Pole and found uniform mixing in the lower atmosphere, and slightly less CFC in the stratosphere.
Newsletter Get smart. Sign up for our email newsletter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. Jean M. For example, the two gases carbon tetrafluoride CF 4 , produced mainly as a by-product of the manufacture of aluminum and CFC CCl 3 F, used in a variety of human activities are both heavier than air.
Carbon tetrafluoride is completely unreactive at altitudes up to at least 50 kilometers in the atmosphere. Measurements show it to be nearly uniformly distributed throughout the atmosphere as illustrated in the figure below, the abundance of CF 4 is nearly the same at all altitudes where measurements have been made.
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