scholarly journals Evaluation of the Australian Community Climate and Earth-System Simulator Chemistry-Climate Model

2015 ◽  
Vol 15 (13) ◽  
pp. 19161-19196
Author(s):  
K. A. Stone ◽  
O. Morgenstern ◽  
D. J. Karoly ◽  
A. R. Klekociuk ◽  
W. J. R. French ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Zonal Wind ◽  
Ozone Depletion ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Similar Amount ◽  
Earth System ◽  
Total Column Ozone ◽  
Australian Community ◽  
Community Climate

Abstract. Chemistry climate models are important tools for addressing interactions of composition and climate in the Earth System. In particular, they are used for assessing the combined roles of greenhouse gases and ozone in Southern Hemisphere climate and weather. Here we present an evaluation of the Australian Community Climate and Earth System Simulator-Chemistry Climate Model, focusing on the Southern Hemisphere and the Australian region. This model is used for the Australian contribution to the international Chemistry-Climate Model Initiative, which is soliciting hindcast, future projection and sensitivity simulations. The model simulates global total column ozone (TCO) distributions accurately, with a slight delay in the onset and recovery of springtime Antarctic ozone depletion, and consistently higher ozone values. However, October averaged Antarctic TCO from 1960 to 2010 show a similar amount of depletion compared to observations. A significant innovation is the evaluation of simulated vertical profiles of ozone and temperature with ozonesonde data from Australia, New Zealand and Antarctica from 38 to 90° S. Excess ozone concentrations (up to 26.4 % at Davis during winter) and stratospheric cold biases (up to 10.1 K at the South Pole) outside the period of perturbed springtime ozone depletion are seen during all seasons compared to ozonesondes. A disparity in the vertical location of ozone depletion is seen: centered around 100 hPa in ozonesonde data compared to above 50 hPa in the model. Analysis of vertical chlorine monoxide profiles indicates that colder Antarctic stratospheric temperatures (possibly due to reduced mid-latitude heat flux) are artificially enhancing polar stratospheric cloud formation at high altitudes. The models inability to explicitly simulated supercooled ternary solution may also explain the lack of depletion at lower altitudes. The simulated Southern Annular Mode (SAM) index compares well with ERA-Interim data. Accompanying these modulations of the SAM, 50 hPa zonal wind differences between 2001–2010 and 1979–1998 show increasing zonal wind strength southward of 60° S during December for both the model simulations and ERA-Interim data. These model diagnostics shows that the model reasonably captures the stratospheric ozone driven chemistry-climate interactions important for Australian climate and weather while highlighting areas for future model development.

scholarly journals Evaluation of the ACCESS – chemistry–climate model for the Southern Hemisphere

2016 ◽  
Vol 16 (4) ◽  
pp. 2401-2415 ◽  
Author(s):  
Kane A. Stone ◽  
Olaf Morgenstern ◽  
David J. Karoly ◽  
Andrew R. Klekociuk ◽  
W. John French ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Zonal Wind ◽  
Ozone Depletion ◽  
Climate Model ◽  
Similar Amount ◽  
Earth System ◽  
South Pole ◽  
The South ◽  
Total Column Ozone ◽  
Australian Climate

Abstract. Chemistry–climate models are important tools for addressing interactions of composition and climate in the Earth system. In particular, they are used to assess the combined roles of greenhouse gases and ozone in Southern Hemisphere climate and weather. Here we present an evaluation of the Australian Community Climate and Earth System Simulator – chemistry–climate model (ACCESS-CCM), focusing on the Southern Hemisphere and the Australian region. This model is used for the Australian contribution to the international Chemistry–Climate Model Initiative, which is soliciting hindcast, future projection and sensitivity simulations. The model simulates global total column ozone (TCO) distributions accurately, with a slight delay in the onset and recovery of springtime Antarctic ozone depletion, and consistently higher ozone values. However, October-averaged Antarctic TCO from 1960 to 2010 shows a similar amount of depletion compared to observations. Comparison with model precursors shows large improvements in the representation of the Southern Hemisphere stratosphere, especially in TCO concentrations. A significant innovation is seen in the evaluation of simulated vertical profiles of ozone and temperature with ozonesonde data from Australia, New Zealand and Antarctica from 38 to 90° S. Excess ozone concentrations (greater than 26 % at Davis and the South Pole during winter) and stratospheric cold biases (up to 10 K at the South Pole during summer and autumn) outside the period of perturbed springtime ozone depletion are seen during all seasons compared to ozonesondes. A disparity in the vertical location of ozone depletion is seen: centred around 100 hPa in ozonesonde data compared to above 50 hPa in the model. Analysis of vertical chlorine monoxide profiles indicates that colder Antarctic stratospheric temperatures (possibly due to reduced mid-latitude heat flux) are artificially enhancing polar stratospheric cloud formation at high altitudes. The model's inability to explicitly simulate a supercooled ternary solution may also explain the lack of depletion at lower altitudes. Analysis of the simulated Southern Annular Mode (SAM) index compares well with ERA-Interim data, an important metric for correct representation of Australian climate. Accompanying these modulations of the SAM, 50 hPa zonal wind differences between 2001–2010 and 1979–1998 show increasing zonal wind strength southward of 60° S during December for both the model simulations and ERA-Interim data. These model diagnostics show that the model reasonably captures the stratospheric ozone-driven chemistry–climate interactions important for Australian climate and weather while highlighting areas for future model development.

scholarly journals Sensitivity of the southern hemisphere tropospheric jet response to Antarctic ozone depletion: prescribed versus interactive chemistry

2020 ◽  
Author(s):  
Sabine Haase ◽  
Jaika Fricke ◽  
Tim Kruschke ◽  
Sebastian Wahl ◽  
Katja Matthes
Keyword(s):  
Southern Hemisphere ◽  
Ozone Depletion ◽  
Climate Models ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Austral Summer ◽  
Jet Stream ◽  
Heating Rates ◽  
Sea Ice Extent ◽  
Poleward Shift

Abstract. Southern hemisphere lower stratospheric ozone depletion has been shown to lead to a poleward shift of the tropospheric jet stream during austral summer, influencing surface atmosphere and ocean conditions, such as surface temperatures and sea ice extent. The characteristics of stratospheric and tropospheric responses to ozone depletion, however, differ largely among climate models depending on the representation of ozone in the models. The most accurate way to represent ozone in a model is to calculate it interactively. However, due to computational costs, in particular for long-term coupled ocean-atmosphere model integrations, the more common way is to prescribe ozone from observations or calculated model fields. Here, we investigate the difference between an interactive and a specified chemistry version of the same atmospheric model in a fully-coupled setup using a 9-member chemistry-climate model ensemble. In the specified chemistry version of the model the ozone fields are prescribed using the output from the interactive chemistry model version. In contrast to earlier studies, we use daily-resolved ozone fields in the specified chemistry simulations to achieve a better comparability between the ozone forcing with and without interactive chemistry. We find that although the short-wave heating rate trend in response to ozone depletion is the same in the different chemistry settings, the interactive chemistry ensemble shows a stronger trend in polar cap stratospheric temperatures (by about 0.7 K per decade) and circumpolar stratospheric zonal mean zonal winds (by about 1.6 m/s per decade) as compared to the specified chemistry ensemble. This difference between interactive and specified chemistry in the stratospheric response to ozone depletion also affects the tropospheric response, namely the poleward shift of the tropospheric jet stream. We attribute part of these differences to the missing representation of feedbacks between chemistry and dynamics in the specified chemistry ensemble, which affect the dynamical heating rates, and part of it to the lack of spatial asymmetries in the prescribed ozone fields. This effect is investigated using a sensitivity ensemble that was forced by a three-dimensional instead of a two–dimensional ozone field. This study emphasizes the value of interactive chemistry for the representation of the southern hemisphere tropospheric jet response to ozone depletion and infers that for periods with strong ozone variability (trends) the details of the ozone forcing can be crucial for representing southern hemispheric climate variability.

scholarly journals Sensitivity of the Southern Hemisphere circumpolar jet response to Antarctic ozone depletion: prescribed versus interactive chemistry

2020 ◽  
Vol 20 (22) ◽  
pp. 14043-14061
Author(s):  
Sabine Haase ◽  
Jaika Fricke ◽  
Tim Kruschke ◽  
Sebastian Wahl ◽  
Katja Matthes
Keyword(s):  
Southern Hemisphere ◽  
Ozone Depletion ◽  
Climate Models ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Austral Summer ◽  
Jet Stream ◽  
Heating Rates ◽  
Sea Ice Extent ◽  
Poleward Shift

Abstract. Southern Hemisphere lower-stratospheric ozone depletion has been shown to lead to a poleward shift of the tropospheric jet stream during austral summer, influencing surface atmosphere and ocean conditions, such as surface temperatures and sea ice extent. The characteristics of stratospheric and tropospheric responses to ozone depletion, however, differ among climate models depending on the representation of ozone in the models. The most appropriate way to represent ozone in a model is to calculate it interactively. However, due to computational costs, in particular for long-term coupled ocean–atmosphere model integrations, the more common way is to prescribe ozone from observations or calculated model fields. Here, we investigate the difference between an interactive and a specified chemistry version of the same atmospheric model in a fully coupled setup using a nine-member chemistry–climate model ensemble. In the specified chemistry version of the model the ozone fields are prescribed using the output from the interactive chemistry model version. We use daily resolved ozone fields in the specified chemistry simulations to achieve a very good comparability between the ozone forcing with and without interactive chemistry. We find that although the shortwave heating rate trend in response to ozone depletion is the same in the different chemistry settings, the interactive chemistry ensemble shows a stronger trend in polar cap stratospheric temperatures (by about 0.7 K decade−1) and circumpolar stratospheric zonal mean zonal winds (by about 1.6 m s−1 decade−1 as compared to the specified chemistry ensemble. This difference between interactive and specified chemistry in the stratospheric response to ozone depletion also affects the tropospheric response. However, an impact on the poleward shift of the tropospheric jet stream is not detected. We attribute part of the differences found in the experiments to the missing representation of feedbacks between chemistry and dynamics in the specified chemistry ensemble, which affect the dynamical heating rates, and part of it to the lack of spatial asymmetries in the prescribed ozone fields. This effect is investigated using a sensitivity ensemble that was forced by a three-dimensional instead of a two-dimensional ozone field. This study emphasizes the value of interactive chemistry for the representation of the Southern Hemisphere stratospheric-jet response to ozone depletion and infers that for periods with strong ozone variability (trends) the details of the ozone forcing could also have an influence on the representation of southern-hemispheric climate variability.

scholarly journals The Toba supervolcano eruption caused severe tropical stratospheric ozone depletion

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Sergey Osipov ◽  
Georgiy Stenchikov ◽  
Kostas Tsigaridis ◽  
Allegra N. LeGrande ◽  
Susanne E. Bauer ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Water Cycle ◽  
Stratospheric Ozone ◽  
System Model ◽  
Earth System ◽  
Sulfate Aerosols ◽  
Winter Conditions ◽  
Attenuation Mechanism ◽  
The Tropics ◽  
Sulfur Emissions

AbstractSupervolcano eruptions have occurred throughout Earth’s history and have major environmental impacts. These impacts are mostly associated with the attenuation of visible sunlight by stratospheric sulfate aerosols, which causes cooling and deceleration of the water cycle. Supereruptions have been assumed to cause so-called volcanic winters that act as primary evolutionary factors through ecosystem disruption and famine, however, winter conditions alone may not be sufficient to cause such disruption. Here we use Earth system model simulations to show that stratospheric sulfur emissions from the Toba supereruption 74,000 years ago caused severe stratospheric ozone loss through a radiation attenuation mechanism that only moderately depends on the emission magnitude. The Toba plume strongly inhibited oxygen photolysis, suppressing ozone formation in the tropics, where exceptionally depleted ozone conditions persisted for over a year. This effect, when combined with volcanic winter in the extra-tropics, can account for the impacts of supereruptions on ecosystems and humanity.

scholarly journals Ozone database in support of CMIP5 simulations: results and corresponding radiative forcing

2011 ◽  
Vol 11 (4) ◽  
pp. 10875-10933 ◽  
Author(s):  
I. Cionni ◽  
V. Eyring ◽  
J. F. Lamarque ◽  
W. J. Randel ◽  
D. S. Stevenson ◽  
...  
Keyword(s):  
Time Series ◽  
Ozone Depletion ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Satellite Observations ◽  
High Latitudes ◽  
The Future ◽  
Column Ozone

Abstract. A continuous tropospheric and stratospheric vertically resolved ozone time series, from 1850 to 2099, has been generated to be used as forcing in global climate models that do not include interactive chemistry. A multiple linear regression analysis of SAGE I+II satellite observations and polar ozonesonde measurements is used for the stratospheric zonal mean dataset during the well-observed period from 1979 to 2009. In addition to terms describing the mean annual cycle, the regression includes terms representing equivalent effective stratospheric chlorine (EESC) and the 11-yr solar cycle variability. The EESC regression fit coefficients, together with pre-1979 EESC values, are used to extrapolate the stratospheric ozone time series backward to 1850. While a similar procedure could be used to extrapolate into the future, coupled chemistry climate model (CCM) simulations indicate that future stratospheric ozone abundances are likely to be significantly affected by climate change, and capturing such effects through a regression model approach is not feasible. Therefore, the stratospheric ozone dataset is extended into the future (merged in 2009) with multi-model mean projections from 13 CCMs that performed a simulation until 2099 under the SRES (Special Report on Emission Scenarios) A1B greenhouse gas scenario and the A1 adjusted halogen scenario in the second round of the Chemistry-Climate Model Validation (CCMVal-2) Activity. The stratospheric zonal mean ozone time series is merged with a three-dimensional tropospheric data set extracted from simulations of the past by two CCMs (CAM3.5 and PUCCINI) and of the future by one CCM (CAM3.5). The future tropospheric ozone time series continues the historical CAM3.5 simulation until 2099 following the four different Representative Concentration Pathways (RCPs). Generally good agreement is found between the historical segment of the ozone database and satellite observations, although it should be noted that total column ozone is overestimated in the southern polar latitudes during spring and tropospheric column ozone is slightly underestimated. Vertical profiles of tropospheric ozone are broadly consistent with ozonesondes and in-situ measurements, with some deviations in regions of biomass burning. The tropospheric ozone radiative forcing (RF) from the 1850s to the 2000s is 0.23 W m−2, lower than previous results. The lower value is mainly due to (i) a smaller increase in biomass burning emissions; (ii) a larger influence of stratospheric ozone depletion on upper tropospheric ozone at high southern latitudes; and possibly (iii) a larger influence of clouds (which act to reduce the net forcing) compared to previous radiative forcing calculations. Over the same period, decreases in stratospheric ozone, mainly at high latitudes, produce a RF of −0.08 W m−2, which is more negative than the central Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) value of −0.05 W m−2, but which is within the stated range of −0.15 to +0.05 W m−2. The more negative value is explained by the fact that the regression model simulates significant ozone depletion prior to 1979, in line with the increase in EESC and as confirmed by CCMs, while the AR4 assumed no change in stratospheric RF prior to 1979. A negative RF of similar magnitude persists into the future, although its location shifts from high latitudes to the tropics. This shift is due to increases in polar stratospheric ozone, but decreases in tropical lower stratospheric ozone, related to a strengthening of the Brewer-Dobson circulation, particularly through the latter half of the 21st century. Differences in trends in tropospheric ozone among the four RCPs are mainly driven by different methane concentrations, resulting in a range of tropospheric ozone RFs between 0.4 and 0.1 W m−2 by 2100. The ozone dataset described here has been released for the Coupled Model Intercomparison Project (CMIP5) model simulations in netCDF Climate and Forecast (CF) Metadata Convention at the PCMDI website (http://cmip-pcmdi.llnl.gov/).

scholarly journals The importance of interactive chemistry for stratosphere–troposphere coupling

2019 ◽  
Vol 19 (5) ◽  
pp. 3417-3432 ◽  
Author(s):  
Sabine Haase ◽  
Katja Matthes
Keyword(s):  
Ozone Depletion ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Ocean Model ◽  
Recent Past ◽  
Stratospheric Polar Vortex ◽  
Model Version ◽  
Surface Climate ◽  
The Mean ◽  
Mean State

Abstract. Recent observational and modeling studies suggest that stratospheric ozone depletion not only influences the surface climate in the Southern Hemisphere (SH), but also impacts Northern Hemisphere (NH) spring, which implies a strong interaction between dynamics and chemistry. Here, we systematically analyze the importance of interactive chemistry with respect to the representation of stratosphere–troposphere coupling and in particular the effects on NH surface climate during the recent past. We use the interactive and specified chemistry version of NCAR's Whole Atmosphere Community Climate Model coupled to an ocean model to investigate differences in the mean state of the NH stratosphere as well as in stratospheric extreme events, namely sudden stratospheric warmings (SSWs), and their surface impacts. To be able to focus on differences that arise from two-way interactions between chemistry and dynamics in the model, the specified chemistry model version uses a time-evolving, model-consistent ozone field generated by the interactive chemistry model version. We also test the effects of zonally symmetric versus asymmetric prescribed ozone, evaluating the importance of ozone waves in the representation of stratospheric mean state and variability. The interactive chemistry simulation is characterized by a significantly stronger and colder polar night jet (PNJ) during spring when ozone depletion becomes important. We identify a negative feedback between lower stratospheric ozone and atmospheric dynamics during the breakdown of the stratospheric polar vortex in the NH, which contributes to the different characteristics of the PNJ between the simulations. Not only the mean state, but also stratospheric variability is better represented in the interactive chemistry simulation, which shows a more realistic distribution of SSWs as well as a more persistent surface impact afterwards compared with the simulation where the feedback between chemistry and dynamics is switched off. We hypothesize that this is also related to the feedback between ozone and dynamics via the intrusion of ozone-rich air into polar latitudes during SSWs. The results from the zonally asymmetric ozone simulation are closer to the interactive chemistry simulations, implying that under a model-consistent ozone forcing, a three-dimensional (3-D) representation of the prescribed ozone field is desirable. This suggests that a 3-D ozone forcing, as recommended for the upcoming CMIP6 simulations, has the potential to improve the representation of stratospheric dynamics and chemistry. Our findings underline the importance of the representation of interactive chemistry and its feedback on the stratospheric mean state and variability not only in the SH but also in the NH during the recent past.

Large Increase in Incident Shortwave Radiation due to the Ozone Hole Offset by High Climatological Albedo over Antarctica

2017 ◽  
Vol 30 (13) ◽  
pp. 4883-4890 ◽  
Author(s):  
G. Chiodo ◽  
L. M. Polvani ◽  
M. Previdi
Keyword(s):  
Surface Temperature ◽  
Ozone Depletion ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Surface Energy Budget ◽  
Ozone Hole ◽  
Radiative Heating ◽  
Shortwave Radiation ◽  
Stratospheric Ozone Depletion ◽  
Continental Scale

Despite increasing scientific scrutiny in recent years, the direct impact of the ozone hole on surface temperatures over Antarctica remains uncertain. Here, this question is explored by using the Community Earth System Model–Whole Atmosphere Community Climate Model (CESM-WACCM), contrasting two ensembles of runs with and without stratospheric ozone depletion. It is found that, during austral spring, the ozone hole leads to a surprisingly large increase in surface downwelling shortwave (SW) radiation over Antarctica of 3.8 W m−2 in clear sky and 1.8 W m−2 in all sky. However, despite this large increase in incident SW radiation, no ozone-induced surface warming is seen in the model. It is shown that the lack of a surface temperature response is due to reflection of most of the increased downward SW, resulting in an insignificant change to the net SW radiative heating. To first order, this reflection is simply due to the high climatological surface albedo of the Antarctic snow (97% in visible SW), resulting in a net zero ozone-induced surface SW forcing. In addition, it is shown that stratospheric ozone depletion has a negligible effect on longwave (LW) radiation and other components of the surface energy budget. These results suggest a minimal role for ozone depletion in forcing Antarctic surface temperature trends on a continental scale.

scholarly journals Ozone Loss and Recovery and the Preconditioning of Upward-Propagating Planetary Wave Activity

2013 ◽  
Vol 70 (12) ◽  
pp. 3977-3994 ◽  
Author(s):  
John R. Albers ◽  
Terrence R. Nathan
Keyword(s):  
Ozone Depletion ◽  
Planetary Wave ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Wave Drag ◽  
Late Winter ◽  
Residual Circulation ◽  
Wave Amplification ◽  
Ozone Loss

Abstract A mechanistic chemistry–dynamical model is used to evaluate the relative importance of radiative, photochemical, and dynamical feedbacks in communicating changes in lower-stratospheric ozone to the circulation of the stratosphere and lower mesosphere. Consistent with observations and past modeling studies of Northern Hemisphere late winter and early spring, high-latitude radiative cooling due to lower-stratospheric ozone depletion causes an increase in the modeled meridional temperature gradient, an increase in the strength of the polar vortex, and a decrease in vertical wave propagation in the lower stratosphere. Moreover, it is shown that, as planetary waves pass through the ozone loss region, dynamical feedbacks precondition the wave, causing a large increase in wave amplitude. The wave amplification causes an increase in planetary wave drag, an increase in residual circulation downwelling, and a weaker polar vortex in the upper stratosphere and lower mesosphere. The dynamical feedbacks responsible for the wave amplification are diagnosed using an ozone-modified refractive index; the results explain recent chemistry–coupled climate model simulations that suggest a link between ozone depletion and increased polar downwelling. The effects of future ozone recovery are also examined and the results provide guidance for researchers attempting to diagnose and predict how stratospheric climate will respond specifically to ozone loss and recovery versus other climate forcings including increasing greenhouse gas abundances and changing sea surface temperatures.

Southern Hemisphere Stationary Wave Response to Changes of Ozone and Greenhouse Gases

2013 ◽  
Vol 26 (24) ◽  
pp. 10205-10217 ◽  
Author(s):  
Lei Wang ◽  
Paul J. Kushner ◽  
Darryn W. Waugh
Keyword(s):  
Phase Shift ◽  
Greenhouse Gases ◽  
Southern Hemisphere ◽  
Ozone Depletion ◽  
Wave Amplitude ◽  
Climate Model ◽  
Recovery Period ◽  
Stationary Wave ◽  
Early Summer ◽  
Model Simulations

Abstract The Southern Hemisphere (SH) stratospheric stationary wave amplitude increased significantly in late spring and early summer during the last two decades of the twentieth century. A suite of chemistry climate model simulations are examined to explore the underlying cause and the separate effects of anthropogenic forcing from ozone depleting substances (ODSs) and greenhouse gases (GHGs) in the past and projected SH stationary wave evolution. The model simulations produce trends in the wave amplitude similar to that observed, although somewhat weaker. In simulations with changing ODSs, this increase in amplitude is reproduced during the ozone depletion period and is reversed during the ozone recovery period. This response is related to changes in the strength and timing of the breakdown of the SH polar vortex associated with ozone depletion and recovery. GHG increases have little impact on the simulated stratospheric stationary wave amplitude but are projected to induce an eastward phase shift of the waves. This phase shift is linked to the strengthening of the subtropical jets driven by GHG forcing via sea surface warming.

scholarly journals Antarctic ozone depletion between 1960 and 1980 in observations and chemistry–climate model simulations

2016 ◽  
Vol 16 (24) ◽  
pp. 15619-15627 ◽  
Author(s):  
Ulrike Langematz ◽  
Franziska Schmidt ◽  
Markus Kunze ◽  
Gregory E. Bodeker ◽  
Peter Braesicke
Keyword(s):  
Ozone Depletion ◽  
Climate Model ◽  
Total Column Ozone ◽  
Antarctic Ozone ◽  
Climate Model Simulations ◽  
Ozone Depleting Substances ◽  
Column Ozone ◽  
The Antarctic ◽  
Total Column

Abstract. The year 1980 has often been used as a benchmark for the return of Antarctic ozone to conditions assumed to be unaffected by emissions of ozone-depleting substances (ODSs), implying that anthropogenic ozone depletion in Antarctica started around 1980. Here, the extent of anthropogenically driven Antarctic ozone depletion prior to 1980 is examined using output from transient chemistry–climate model (CCM) simulations from 1960 to 2000 with prescribed changes of ozone-depleting substance concentrations in conjunction with observations. A regression model is used to attribute CCM modelled and observed changes in Antarctic total column ozone to halogen-driven chemistry prior to 1980. Wintertime Antarctic ozone is strongly affected by dynamical processes that vary in amplitude from year to year and from model to model. However, when the dynamical and chemical impacts on ozone are separated, all models consistently show a long-term, halogen-induced negative trend in Antarctic ozone from 1960 to 1980. The anthropogenically driven ozone loss from 1960 to 1980 ranges between 26.4 ± 3.4 and 49.8 ± 6.2 % of the total anthropogenic ozone depletion from 1960 to 2000. An even stronger ozone decline of 56.4 ± 6.8 % was estimated from ozone observations. This analysis of the observations and simulations from 17 CCMs clarifies that while the return of Antarctic ozone to 1980 values remains a valid milestone, achieving that milestone is not indicative of full recovery of the Antarctic ozone layer from the effects of ODSs.

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