Stratospheric ozone measurements at Arosa (Switzerland):  history and scientific relevance

Abstract. Climatic Observatory (LKO) in Arosa (Switzerland), marking the beginning of the world's longest series of total (or column) ozone measurements. They were driven by the recognition that atmospheric ozone is important for human health, as well as by scientific curiosity about what was, at the time, an ill characterised atmospheric trace gas. From around the mid-1950s to the beginning of the 1970s studies of high atmosphere circulation patterns that could improve weather forecasting was justification for studying stratospheric ozone. In the mid-1970s, a paradigm shift occurred when it became clear that the damaging effects of anthropogenic ozone-depleting substances (ODSs), such as long-lived chlorofluorocarbons, needed to be documented. This justified continuing the ground-based measurements of stratospheric ozone. Levels of ODSs peaked around the mid-1990s as a result of a global environmental policy to protect the ozone layer, implemented through the 1987 Montreal Protocol and its subsequent amendments and adjustments. Consequently, chemical destruction of stratospheric ozone started to slow around the mid-1990s. To some extent, this raises the question as to whether continued ozone observation is indeed necessary. In the last decade there has been a tendency to reduce the costs associated with making ozone measurements globally including at Arosa. However, the large natural variability in ozone on diurnal, seasonal, and interannual scales complicates the capacity for demonstrating the success of the Montreal Protocol. Chemistry-climate models also predict a super-recovery of the ozone layer at mid-latitudes in the second half of this century, i.e. an increase of ozone concentrations beyond pre-1970 levels, as a consequence of ongoing climate change. These factors, and identifying potentially unexpected stratospheric responses to climate change, support the continued need to document stratospheric ozone changes. This is particularly valuable at the Arosa site, due to the unique length of the observational record. This paper presents the evolution of the ozone layer, the history of international ozone research, and discusses the justification for the measurements in the past, present and into future.

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Stratospheric ozone measurements at Arosa (Switzerland): History and scientific relevance

10.5194/acp-2017-1079 ◽

2017 ◽

Author(s):

Johannes Staehelin ◽

Pierre Viatte ◽

Rene Stübi ◽

Fiona Tummon ◽

Thomas Peter

Keyword(s):

Ozone Depletion ◽

Climate Models ◽

Stratospheric Ozone ◽

Cost Savings ◽

Ozone Layer ◽

Montreal Protocol ◽

Global Environmental Policy ◽

History Of ◽

Ozone Depleting Substances ◽

Column Ozone

Abstract. In 1926 the stratospheric ozone measurements of the Light Climatic Observatory (LKO) of Arosa (Switzerland) started, marking the start of the world's longest total (or column) ozone measurements. These measurements were driven by the recognition of the importance of atmospheric ozone for human health as well as by scientific curiosity in this by then not well characterized atmospheric trace gas. Since the mid-1970s ground-based measurements of stratospheric ozone have also been justified to society by the need to document the effects of anthropogenic Ozone Depleting Substances (ODSs), which cause stratospheric ozone depletion. Levels of ODSs peaked around the mid-1990s as a result of a global environmental policy to protect the ozone layer implemented by the 1987 Montreal Protocol and its subsequent amendments and adjustments. Consequently, chemical ozone depletion caused by ODSs stopped worsening around the mid-1990s. This renders justification for continued ozone measurements more difficult, and is likely to do so even more in future, when stratospheric ozone recovery is expected. Tendencies of increased cost savings in ozone measurements seem perceptible worldwide, also in Arosa. However, the large natural variability in ozone on diurnal, seasonal and interannual scales complicates to demonstrate the success of the Montreal Protocol. Moreover, chemistry-climate models predict a “super-recovery” of the ozone layer in the second half of this century, i.e. an increase of ozone concentrations beyond pre-1970 levels, as a consequence of ongoing climate change. This paper presents the evolution of the ozone layer and the history of international ozone research and discusses the justification of these measurements for past, present and future.

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Inconsistencies between chemistry climate model and observed lower stratospheric trends since 1998

10.5194/acp-2019-734 ◽

2019 ◽

Cited By ~ 1

Author(s):

William T. Ball ◽

Gabriel Chiodo ◽

Marta Abalos ◽

Justin Alsing

Keyword(s):

Large Scale ◽

Climate Models ◽

Climate Model ◽

Stratospheric Ozone ◽

Ozone Layer ◽

Montreal Protocol ◽

Total Column Ozone ◽

Temperature Trends ◽

Ozone Depleting Substances ◽

The Tropics

Abstract. The stratospheric ozone layer shields surface life from harmful ultraviolet radiation. Following the Montreal Protocol ban of long-lived ozone depleting substances (ODSs), rapid depletion of total column ozone (TCO) ceased in the late 1990s and ozone above 32 km now enjoys a clear recovery. However, there is still no confirmation of TCO recovery, and evidence has emerged that ongoing quasi-global (60° S–60° N) lower stratospheric ozone decreases may be responsible, dominated by low latitudes (30° S–30° N). Chemistry climate models (CCMs) used to project future changes predict that lower stratospheric ozone will decrease in the tropics by 2100, but not at mid-latitudes (30°–60°). Here, we show that CCMs display an ozone decline similar to that observed in the tropics over 1998–2016, likely driven by a increase of tropical upwelling. On the other hand, mid-latitude lower stratospheric ozone is observed to decrease, while CCMs show an increase. Despite opposing lower stratospheric ozone changes, which should induce opposite temperature trends, CCM and observed temperature trends agree; we demonstrate that opposing model-observation stratospheric water vapour (SWV) trends, and their associated radiative effects, explain why temperature changes agree in spite of opposing ozone trends. We provide new evidence that the observed mid-latitude trends can be explained by enhanced mixing between the tropics and extratropics. We further show that the temperature trends are consistent with the observed mid-latitude ozone decrease. Together, our results suggest that large scale circulation changes expected in the future from increased greenhouse gases (GHGs) may now already be underway, but that most CCMs are not simulating well mid-latitude ozone layer changes. The reason CCMs do not exhibit the observed changes urgently needs to be understood to improve confidence in future projections of the ozone layer.

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Healing the Ozone Layer

Great Policy Successes ◽

10.1093/oso/9780198843719.003.0016 ◽

2019 ◽

pp. 304-322

Author(s):

Frederike Albrecht ◽

Charles F. Parker

Keyword(s):

Gold Standard ◽

Environmental Governance ◽

Stratospheric Ozone ◽

Ozone Layer ◽

Montreal Protocol ◽

Policy Changes ◽

Stratospheric Ozone Layer ◽

Environmental Regimes ◽

Global Environmental ◽

Ozone Depleting Substances

The Montreal Protocol—the regime designed to protect the stratospheric ozone layer—has widely been hailed as the gold standard of global environmental governance and is one of few examples of international institutional cooperative arrangements successfully solving complex transnational problems. Although the stratospheric ozone layer still bears the impacts of ozone depleting substances (ODSs), the problem of ozone depletion is well on its way to being solved due to the protocol. This chapter examines how the protocol was designed and implemented in a way that has allowed it to successfully overcome a number of thorny challenges that most international environmental regimes must face: how to attract sufficient participation, how to promote compliance and manage non-compliance, how to strengthen commitments over time, how to neutralize or co-opt potential ‘veto players’, how to make the costs of implementation affordable, how to leverage public opinion in support of the regime’s goals, and, ultimately, how to promote the behavioural and policy changes needed to solve the problems and achieve the goals the regime was designed to solve. The chapter concludes that while some of the reasons for the Montreal Protocol’s success, such as fairly affordable, available substitutes for ODSs, are not easy to replicate, there are many other elements of this story that can be utilized when thinking about how to design solutions to other transnational environmental problems.

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Evidence for a continuous decline in lower stratospheric ozone offsetting ozone layer recovery

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-1379-2018 ◽

2018 ◽

Vol 18 (2) ◽

pp. 1379-1394 ◽

Cited By ~ 112

Author(s):

William T. Ball ◽

Justin Alsing ◽

Daniel J. Mortlock ◽

Johannes Staehelin ◽

Joanna D. Haigh ◽

...

Keyword(s):

Lower Stratosphere ◽

Stratospheric Ozone ◽

Ozone Layer ◽

Montreal Protocol ◽

Downward Trend ◽

Polar Regions ◽

Total Column Ozone ◽

Ozone Depleting Substances ◽

Column Ozone ◽

Total Column

Abstract. Ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the Brewer–Dobson circulation (BDC), forming a protective ozone layer around the globe. Human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol, and since 1998 ozone in the upper stratosphere is rising again, likely the recovery from halogen-induced losses. Total column measurements of ozone between the Earth's surface and the top of the atmosphere indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes between 60° S and 60° N outside the polar regions (60–90°). Here we report evidence from multiple satellite measurements that ozone in the lower stratosphere between 60° S and 60° N has indeed continued to decline since 1998. We find that, even though upper stratospheric ozone is recovering, the continuing downward trend in the lower stratosphere prevails, resulting in a downward trend in stratospheric column ozone between 60° S and 60° N. We find that total column ozone between 60° S and 60° N appears not to have decreased only because of increases in tropospheric column ozone that compensate for the stratospheric decreases. The reasons for the continued reduction of lower stratospheric ozone are not clear; models do not reproduce these trends, and thus the causes now urgently need to be established.

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Tropospheric temperature response to stratospheric ozone recovery in the 21st century

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-7687-2011 ◽

2011 ◽

Vol 11 (15) ◽

pp. 7687-7699 ◽

Cited By ~ 20

Author(s):

Y. Hu ◽

Y. Xia ◽

Q. Fu

Keyword(s):

21St Century ◽

Climate Models ◽

Stratospheric Ozone ◽

Temperature Response ◽

Ozone Layer ◽

Montreal Protocol ◽

Polar Regions ◽

Tropospheric Temperature ◽

Intergovernmental Panel ◽

Maximum Enhancement

Abstract. Recent simulations predicted that the stratospheric ozone layer will likely return to pre-1980 levels in the middle of the 21st century, as a result of the decline of ozone depleting substances under the Montreal Protocol. Since the ozone layer is an important component in determining stratospheric and tropospheric-surface energy balance, the recovery of stratospheric ozone may have significant impact on tropospheric-surface climate. Here, using multi-model results from both the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC-AR4) models and coupled chemistry-climate models, we show that as ozone recovery is considered, the troposphere is warmed more than that without considering ozone recovery, suggesting an enhancement of tropospheric warming due to ozone recovery. It is found that the enhanced tropospheric warming is mostly significant in the upper troposphere, with a global and annual mean magnitude of ~0.41 K for 2001–2050. We also find that relatively large enhanced warming occurs in the extratropics and polar regions in summer and autumn in both hemispheres, while the enhanced warming is stronger in the Northern Hemisphere than in the Southern Hemisphere. Enhanced warming is also found at the surface. The global and annual mean enhancement of surface warming is about 0.16 K for 2001–2050, with maximum enhancement in the winter Arctic.

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Continuous decline in lower stratospheric ozone offsets ozone layer recovery

10.5194/acp-2017-862 ◽

2017 ◽

Cited By ~ 1

Author(s):

William T. Ball ◽

Justin Alsing ◽

Daniel J. Mortlock ◽

Johannes Staehelin ◽

Joanna D. Haigh ◽

...

Keyword(s):

Respiratory Health ◽

Stratospheric Ozone ◽

Ultra Violet ◽

Ozone Layer ◽

Montreal Protocol ◽

Polar Regions ◽

Total Column Ozone ◽

Ozone Trends ◽

Ozone Depleting Substances ◽

Column Ozone

Abstract. Ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the Brewer-Dobson circulation (BDC), forming a protective ozone layer around the globe. Human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol (MP), and since 1998 ozone in the upper stratosphere shows a likely recovery. Total column ozone (TCO) measurements of ozone between the Earth's surface and the top of the atmosphere, indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes outside the polar regions (60–90). Here we report evidence from multiple satellite measurements that ozone in the lower stratosphere between 60° S and 60° N has declined continuously since 1985. We find that, even though upper stratospheric ozone is recovering in response to the MP, the lower stratospheric changes more than compensate for this, resulting in the conclusion that, globally (60°&tinsp;S–60° N), stratospheric column ozone (StCO) continues to deplete. We find that globally, TCO appears to not have decreased because tropospheric column ozone (TrCO) increases, likely the result of human activity and harmful to respiratory health, are compensating for the stratospheric decreases. The reason for the continued reduction of lower stratospheric ozone is not clear, models do not reproduce these trends, and so the causes now urgently need to be established. Reductions in lower stratospheric ozone trends may partly lead to a small reduction in the warming of the climate, but a reduced ozone layer may also permit an increase in harmful ultra-violet (UV) radiation at the surface and would impact human and ecosystem health.

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Comparison of observed lower stratospheric ozone changes with free-running chemistry climate models

10.5194/egusphere-egu2020-16138 ◽

2020 ◽

Author(s):

William Ball ◽

Gabriel Chiodo ◽

Marta Abalos ◽

Justin Alsing

Keyword(s):

Large Scale ◽

Climate Models ◽

Lower Stratosphere ◽

Stratospheric Ozone ◽

Montreal Protocol ◽

Total Column Ozone ◽

Free Running ◽

Ozone Depleting Substances ◽

Column Ozone ◽

The Tropics

The ozone layer was damaged last century due to the emissions of long-lived ozone depleting substances (ODSs). Following the Montreal Protocol that banned ODSs, a reduction in total column ozone (TCO) ceased in the late 1990s. Today, ozone above 32&#8201;km displays a clear recovery. Nevertheless, a clear detection of TCO recovery in observations remains elusive, and there is mounting evidence of decreasing ozone in the lower stratosphere (below 24 km) in the tropics out to the mid-latitudes (30-60&#176;). Chemistry climate models (CCMs) predict that lower stratospheric ozone will decrease in the tropics by 2100, but not at mid-latitudes. &#160; Here, we compare the CCMVal-2 models, which informed the WMO 2014 ozone assessment and show similar tendencies to more recent CCMI data, with observations over 1998-2016. We find that over this period, modelled ozone declines in the tropics are similar to those seen in observations and are likely driven by increased tropical upwelling. Conversely, CCMs generally show ozone increases in the mid-latitude lower stratosphere where observations show a negative tendency. We provide evidence from JRA-55 and ERA-Interim reanalyses indicating that mid-latitude trends are due to enhanced mixing between the tropics and extratropics, in agreement with other studies.&#160;Additional analysis of temperature and water vapour further supports our findings. Overall, our results suggest that expected changes in large scale circulation from increasing greenhouse gases may now already be underway. While model projections suggest extra-tropical ozone should recover by 2100, our study raises questions about their ability to simulate lower stratospheric changes in this region.

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Inconsistencies between chemistry–climate models and observed lower stratospheric ozone trends since 1998

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-9737-2020 ◽

2020 ◽

Vol 20 (16) ◽

pp. 9737-9752

Author(s):

William T. Ball ◽

Gabriel Chiodo ◽

Marta Abalos ◽

Justin Alsing ◽

Andrea Stenke

Keyword(s):

Large Scale ◽

Climate Models ◽

Stratospheric Ozone ◽

Internal Variability ◽

Ozone Layer ◽

Montreal Protocol ◽

Total Column Ozone ◽

Temperature Trends ◽

Ozone Trends ◽

The Tropics

Abstract. The stratospheric ozone layer shields surface life from harmful ultraviolet radiation. Following the Montreal Protocol ban on long-lived ozone-depleting substances (ODSs), rapid depletion of total column ozone (TCO) ceased in the late 1990s, and ozone above 32 km is now clearly recovering. However, there is still no confirmation of TCO recovery, and evidence has emerged that ongoing quasi-global (60∘ S–60∘ N) lower stratospheric ozone decreases may be responsible, dominated by low latitudes (30∘ S–30∘ N). Chemistry–climate models (CCMs) used to project future changes predict that lower stratospheric ozone will decrease in the tropics by 2100 but not at mid-latitudes (30–60∘). Here, we show that CCMs display an ozone decline similar to that observed in the tropics over 1998–2016, likely driven by an increase in tropical upwelling. On the other hand, mid-latitude lower stratospheric ozone is observed to decrease, while CCMs that specify real-world historical meteorological fields instead show an increase up to present day. However, these cannot be used to simulate future changes; we demonstrate here that free-running CCMs used for projections also show increases. Despite opposing lower stratospheric ozone changes, which should induce opposite temperature trends, CCMs and observed temperature trends agree; we demonstrate that opposing model–observation stratospheric water vapour (SWV) trends, and their associated radiative effects, explain why temperature changes agree in spite of opposing ozone trends. We provide new evidence that the observed mid-latitude trends can be explained by enhanced mixing between the tropics and extratropics. We further show that the temperature trends are consistent with the observed mid-latitude ozone decrease. Together, our results suggest that large-scale circulation changes expected in the future from increased greenhouse gases (GHGs) may now already be underway but that most CCMs do not simulate mid-latitude ozone layer changes well. However, it is important to emphasise that the periods considered here are short, and internal variability that is both intrinsic to each CCM and different to observed historical variability is not well-characterised and can influence trend estimates. Nevertheless, the reason CCMs do not exhibit the observed changes needs to be identified to allow models to be improved in order to build confidence in future projections of the ozone layer.

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The response of the ozone layer under abrupt 4xCO2 in CMIP6

10.5194/egusphere-egu21-15283 ◽

2021 ◽

Author(s):

Gabriel Chiodo ◽

William T. Ball ◽

Peer Nowack ◽

Clara Orbe ◽

James Keeble ◽

...

Keyword(s):

Radiative Forcing ◽

Climate Models ◽

Stratospheric Ozone ◽

Ozone Layer ◽

Cmip5 Models ◽

Radiative Efficiency ◽

Tropospheric Circulation ◽

Column Ozone ◽

The Relationship

Previous studies indicate a possible role of stratospheric ozone chemistry feedbacks in the climate response to 4xCO2, either via a reduction in equilibrium climate sensitivity (ECS) or via changes in the tropospheric circulation (Nowack et al., 2015; Chiodo and Polvani, 2017). However, these effects are subject to uncertainty. Part of the uncertainty may stem from the dependency of the feedback on the pattern of the ozone response, as the radiative efficiency of ozone largely depends on its vertical distribution (Lacis et al., 1990). Here, an analysis is presented of the ozone layer response to 4xCO2 in chemistry&#8211;climate models (CCMs) which participated to CMIP inter-comparisons. In a previous study using CMIP5 models, it has been shown that under 4xCO2, ozone decreases in the tropical lower stratosphere, and increases over the high latitudes and throughout the upper stratosphere (Chiodo et al., 2018). It was also found that a substantial portion of the spread in the tropical column ozone is tied to inter-model spread in tropical upwelling, which is in turn tied to ECS. Here, we revisit this connection using 4xCO2 data from CMIP6, thereby exploiting the larger number of CCMs available than in CMIP5. In addition, we explore the linearity of the ozone response, by complementing the analysis with simulations using lower CO2 forcing levels (2xCO2). We show that the pattern of the ozone response is similar to CMIP5. In some models (e.g. WACCM), we find larger ozone responses in CMIP6 than in CMIP5, partly because of the larger ECS and thus larger upwelling response in the tropical pipe. In this presentation, we will discuss the relationship between radiative forcing, transport and ozone, as well as further implications for CMIP6 models.

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Atmospheric impacts of short-lived chlorinated species over the recent past: a chemistry-climate perspective

10.5194/egusphere-egu21-12824 ◽

2021 ◽

Author(s):

Ewa Bednarz ◽

Ryan Hossaini ◽

Luke Abraham ◽

Peter Braesicke ◽

Martyn Chipperfield

Keyword(s):

Atmospheric Chemistry ◽

Climate Model ◽

Stratospheric Ozone ◽

Lower Boundary ◽

Montreal Protocol ◽

Recent Past ◽

Substantial Impact ◽

Ozone Depleting Substances ◽

The Impact

The emissions of most long-lived halogenated ozone-depleting substances (ODSs) are now decreasing, owing to controls on their production introduced by Montreal Protocol and its amendments. However, short-lived halogenated compounds can also have substantial impact on atmospheric chemistry, including stratospheric ozone, particularly if emitted near climatological uplift regions. It has recently become evident that emissions of some chlorinated very short-lived species (VSLSs), such as chloroform (CHCl3) and dichloromethane (CH2Cl2), could be larger than previously believed and increasing, particularly in Asia. While these may exert a significant influence on atmospheric chemistry and climate, their impacts remain poorly characterised.&#160;&#160;We address this issue using the UM-UKCA chemistry-climate model (CCM). While not only the first, to our knowledge, model study addressing this problem using a CCM, it is also the first such study employing a whole atmosphere model, thereby simulating the tropospheric Cl-VSLSs emissions and the resulting stratospheric impacts in a fully consistent manner. We use a newly developed Double-Extended Stratospheric-Tropospheric (DEST) chemistry scheme, which includes emissions of all major chlorinated and brominated VSLSs alongside an extended treatment of long-lived ODSs.&#160;We examine the impacts of rising Cl-VSLSs emissions on atmospheric chlorine tracers and ozone, including their long-term trends. We pay particular attention to the role of &#8216;nudging&#8217;, as opposed to the free-running model set up, for the simulated Cl-VSLSs impacts, thereby demostrating the role of atmospheric dynamics in modulating the atmospheric responses to Cl-VSLSs. In addition, we employ novel estimates of Cl-VSLS emissions over the recent past and compare the results with the simulations that prescribe Cl-VSLSs using simple lower boundary conditions. This allows us to demonstrate the impact such choice has on the dominant location and seasonality of the Cl-VSLSs transport into the stratosphere.

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