Browsing by Author "Steinbrecht, Wolfgang"

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    Detecting recovery of the stratospheric ozone layer
    (Nature Publishing Group, 2017-09-13) Chipperfield, Martyn P.; Bekki, Slimane; Dhomse, Sandip; Harris, Neil; Hassler, Birgit; Hossaini, Ryan; Steinbrecht, Wolfgang; Thiéblemont, Rémi; Weber, Mark
    As a result of the 1987 Montreal Protocol and its amendments, the atmospheric loading of anthropogenic ozone-depleting substances is decreasing. Accordingly, the stratospheric ozone layer is expected to recover. However, short data records and atmospheric variability confound the search for early signs of recovery, and climate change is masking ozone recovery from ozone-depleting substances in some regions and will increasingly affect the extent of recovery. Here we discuss the nature and timescales of ozone recovery, and explore the extent to which it can be currently detected in different atmospheric regions.
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    Is global ozone recovering?
    (Elsevier, 2018-10-13) Steinbrecht, Wolfgang; Hegglin, Michaela I.; Harris, Neil; Weber, Mark
    Thanks to the Montreal Protocol, the stratospheric concentrations of ozone-depleting chlorine and bromine have been declining since their peak in the late 1990s. Global ozone has responded: The substantial ozone decline observed since the 1960s ended in the late 1990s. Since then, ozone levels have remained low, but have not declined further. Now general ozone increases and a slow recovery of the ozone layer is expected. The clearest signs of increasing ozone, so far, are seen in the upper stratosphere and for total ozone columns above Antarctica in spring. These two regions had also seen the largest ozone depletions in the past. Total column ozone at most latitudes, however, does not show clear increases yet. This is not unexpected, because the removal of chlorine and bromine from the stratosphere is three to four times slower than their previous increase. Detecting significant increases in total column ozone, therefore, will require much more time than the detection of its previous decline. The search is complicated by variations in ozone that are not caused by declining chlorine or bromine, but are due, e.g., to transport changes in the global Brewer–Dobson circulation. Also, very accurate observations are necessary to detect the expected small increases. Nevertheless, observations and model simulations indicate that the stratosphere is on the path to ozone recovery. This recovery process will take many decades. As chlorine and bromine decline, other factors will become more important. These include climate change and its effects on stratospheric temperatures, changes in the Brewer–Dobson circulation (both due to increasing CO2), increasing emissions of trace gases like N2O, CH4, possibly large future increases of short-lived substances (like CCl2H2) from both natural and anthropogenic sources, and changes in tropospheric ozone.
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    An update on ozone profile trends for the period 2000 to 2016
    (European Geosciences Union (EGU) / Copernicus Publications, 2017-09-11) Steinbrecht, Wolfgang; Froidevaux, Lucien; Fuller, Ryan; Wang, Ray; Anderson, John; Roth, Chris; Bourassa, Adam; Degenstein, Doug; Damadeo, Robert; Zawodny, Joe; Frith, Stacey; McPeters, Richard; Bhartia, Pawan; Wild, Jeannette; Long, Craig; Davis, Sean; Rosenlof, Karen; Sofieva, Viktoria; Walker, Kaley; Rahpoe, Nabiz; Rozanov, Alexei; Weber, Mark; Laeng, Alexandra; von Clarmann, Thomas; Stiller, Gabriele; Kramarova, Natalya; Godin-Beekmann, Sophie; Leblanc, Thierry; Querel, Richard; Swart, Daan; Boyd, Ian; Hocke, Klemens; Kämpfer, Niklaus; Maillard Barras, Eliane; Moreira, Lorena; Nedoluha, Gerald; Vigouroux, Corinne; Blumenstock, Thomas; Schneider, Matthias; García, Omaira; Jones, Nicholas; Mahieu, Emmanuel; Smale, Dan; Kotkamp, Michael; Robinson, John; Petropavlovskikh, Irina; Harris, Neil; Hassler, Birgit; Hubert, Daan; Tummon, Fiona
    Ozone profile trends over the period 2000 to 2016 from several merged satellite ozone data sets and from ground-based data measured by four techniques at stations of the Network for the Detection of Atmospheric Composition Change indicate significant ozone increases in the upper stratosphere, between 35 and 48 km altitude (5 and 1 hPa). Near 2 hPa (42 km), ozone has been increasing by about 1.5 % per decade in the tropics (20° S to 20° N), and by 2 to 2.5 % per decade in the 35 to 60° latitude bands of both hemispheres. At levels below 35 km (5 hPa), 2000 to 2016 ozone trends are smaller and not statistically significant. The observed trend profiles are consistent with expectations from chemistry climate model simulations. This study confirms positive trends of upper stratospheric ozone already reported, e.g., in the WMO/UNEP Ozone Assessment 2014 or by Harris et al. (2015). Compared to those studies, three to four additional years of observations, updated and improved data sets with reduced drift, and the fact that nearly all individual data sets indicate ozone increase in the upper stratosphere, all give enhanced confidence. Uncertainties have been reduced, for example for the trend near 2 hPa in the 35 to 60° latitude bands from about ±5 % (2σ) in Harris et al. (2015) to less than ±2 % (2σ). Nevertheless, a thorough analysis of possible drifts and differences between various data sources is still required, as is a detailed attribution of the observed increases to declining ozone-depleting substances and to stratospheric cooling. Ongoing quality observations from multiple independent platforms are key for verifying that recovery of the ozone layer continues as expected.