scholarly journals The Importance of the Montreal Protocol in Protecting Earth’s Hydroclimate

2013 ◽  
Vol 26 (12) ◽  
pp. 4049-4068 ◽  
Author(s):  
Yutian Wu ◽  
Lorenzo M. Polvani ◽  
Richard Seager
Keyword(s):  
Ozone Depletion ◽  
Radiative Forcing ◽  
Hydrological Cycle ◽  
Stratospheric Ozone ◽  
Atmospheric Model ◽  
Ultraviolet B ◽  
Montreal Protocol ◽  
Mixed Layer Ocean ◽  
The World ◽  
Ozone Depleting Substances

Abstract The 1987 Montreal Protocol regulating emissions of chlorofluorocarbons (CFCs) and other ozone-depleting substances (ODSs) was motivated primarily by the harm to human health and ecosystems arising from increased exposure to ultraviolet-B (UV-B) radiation associated with depletion of the ozone layer. It is now known that the Montreal Protocol has helped reduce radiative forcing of the climate system since CFCs are greenhouse gases (GHGs), and that ozone depletion (which is now on the verge of reversing) has been the dominant driver of atmospheric circulation changes in the Southern Hemisphere in the last half century. This paper demonstrates that the Montreal Protocol also significantly protects Earth’s hydroclimate. Using the Community Atmospheric Model, version 3 (CAM3), coupled to a simple mixed layer ocean, it is shown that in the “world avoided” (i.e., with CFC emissions not regulated), the subtropical dry zones would be substantially drier, and the middle- and high-latitude regions considerably wetter in the coming decade (2020–29) than in a world without ozone depletion. Surprisingly, these changes are very similar, in both pattern and magnitude, to those caused by projected increases in GHG concentrations over the same period. It is further shown that, by dynamical and thermodynamical mechanisms, both the stratospheric ozone depletion and increased CFCs contribute to these changes. The results herein imply that, as a consequence of the Montreal Protocol, changes in the hydrological cycle in the coming decade will be only half as strong as what they otherwise would be.

scholarly journals Options to accelerate ozone recovery: ozone and climate benefits

2010 ◽  
Vol 10 (16) ◽  
pp. 7697-7707 ◽  
Author(s):  
J. S. Daniel ◽  
E. L. Fleming ◽  
R. W. Portmann ◽  
G. J. M. Velders ◽  
C. H. Jackman ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Radiative Forcing ◽  
Montreal Protocol ◽  
N2o Emissions ◽  
Total Column Ozone ◽  
Potential Impact ◽  
Ozone Depleting Substances ◽  
Column Ozone ◽  
The Impact ◽  
Total Column

Abstract. Hypothetical reductions in future emissions of ozone-depleting substances (ODSs) and N2O are evaluated in terms of effects on equivalent effective stratospheric chlorine (EESC), globally-averaged total column ozone, and radiative forcing through 2100. Due to the established success of the Montreal Protocol, these actions can have only a fraction of the impact on ozone depletion that regulations already in force have had. If all anthropogenic ODS and N2O emissions were halted beginning in 2011, ozone is calculated to be higher by about 1–2% during the period 2030–2100 compared to a case of no additional restrictions. Direct radiative forcing by 2100 would be about 0.23 W/m2 lower from the elimination of anthropogenic N2O emissions and about 0.005 W/m2 lower from the destruction of the chlorofluorocarbon (CFC) bank. Due to the potential impact of N2O on future ozone levels, we provide an approach to incorporate it into the EESC formulation, which is used extensively in ozone depletion analyses. The ability of EESC to describe total ozone changes arising from additional ODS and N2O controls is also quantified.

scholarly journals Stratospheric ozone depletion

2006 ◽  
Vol 361 (1469) ◽  
pp. 769-790 ◽  
Author(s):  
F. Sherwood Rowland
Keyword(s):  
Ultraviolet Radiation ◽  
Ozone Depletion ◽  
Biological Activities ◽  
Stratospheric Ozone ◽  
Ozone Layer ◽  
Ultraviolet B ◽  
Montreal Protocol ◽  
Atmospheric Measurements ◽  
Solar Ultraviolet Radiation ◽  
Solar Ultraviolet

Solar ultraviolet radiation creates an ozone layer in the atmosphere which in turn completely absorbs the most energetic fraction of this radiation. This process both warms the air, creating the stratosphere between 15 and 50 km altitude, and protects the biological activities at the Earth's surface from this damaging radiation. In the last half-century, the chemical mechanisms operating within the ozone layer have been shown to include very efficient catalytic chain reactions involving the chemical species HO, HO 2 , NO, NO 2 , Cl and ClO. The NO X and ClO X chains involve the emission at Earth's surface of stable molecules in very low concentration (N 2 O, CCl 2 F 2 , CCl 3 F, etc.) which wander in the atmosphere for as long as a century before absorbing ultraviolet radiation and decomposing to create NO and Cl in the middle of the stratospheric ozone layer. The growing emissions of synthetic chlorofluorocarbon molecules cause a significant diminution in the ozone content of the stratosphere, with the result that more solar ultraviolet-B radiation (290–320 nm wavelength) reaches the surface. This ozone loss occurs in the temperate zone latitudes in all seasons, and especially drastically since the early 1980s in the south polar springtime—the ‘Antarctic ozone hole’. The chemical reactions causing this ozone depletion are primarily based on atomic Cl and ClO, the product of its reaction with ozone. The further manufacture of chlorofluorocarbons has been banned by the 1992 revisions of the 1987 Montreal Protocol of the United Nations. Atmospheric measurements have confirmed that the Protocol has been very successful in reducing further emissions of these molecules. Recovery of the stratosphere to the ozone conditions of the 1950s will occur slowly over the rest of the twenty-first century because of the long lifetime of the precursor molecules.

Emergence of Southern Hemisphere circulation changes in response to ozone recovery

2020 ◽  
Author(s):  
Brian Zambri ◽  
Susan Solomon ◽  
David Thompson ◽  
Qiang Fu
Keyword(s):  
Southern Hemisphere ◽  
Ozone Depletion ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Montreal Protocol ◽  
Stratospheric Polar Vortex ◽  
Surface Climate ◽  
Antarctic Ozone ◽  
Ozone Depleting Substances ◽  
Circulation Changes

<p>Ozone depletion in the Southern Hemisphere (SH) stratosphere in the late 20<sup>th</sup> century cooled the air there, strengthening the SH stratospheric westerly winds near 60ºS and altering SH surface climate. Since ~1999, trends in Antarctic ozone have begun to recover, exhibiting a flattening followed by a sign reversal in response to decreases in stratospheric chlorine concentration due to the Montreal Protocol, an international treaty banning the production and consumption of ozone-depleting substances. Here we show that the post–1999 increase in ozone has resulted in thermal and circulation changes of opposite sign to those that resulted from stratospheric ozone losses, including a warming of the SH polar lower stratosphere and a weakening of the SH stratospheric polar vortex.  Further, these altered trends extend to the upper troposphere, albeit of smaller magnitudes.  Observed post–1999 trends of temperature and circulation in the stratosphere are about 20–25% the magnitude of those of the ozone depletion era, and are broadly consistent with expectations based on modeled depletion-era trends and variability of both ozone and reactive chlorine, thereby indicating the emergence of healing of dynamical impacts of the Antarctic ozone hole.</p>

scholarly journals Linkages between ozone-depleting substances, tropospheric oxidation and aerosols

2013 ◽  
Vol 13 (9) ◽  
pp. 4907-4916 ◽  
Author(s):  
A. Voulgarakis ◽  
D. T. Shindell ◽  
G. Faluvegi
Keyword(s):  
Radiative Forcing ◽  
Scale Effects ◽  
Stratospheric Ozone ◽  
Montreal Protocol ◽  
Tropospheric Chemistry ◽  
Atmospheric Composition ◽  
N2o Emissions ◽  
Sulfate Aerosols ◽  
Comparable Amount ◽  
Ozone Depleting Substances

Abstract. Coupling between the stratosphere and the troposphere allows changes in stratospheric ozone abundances to affect tropospheric chemistry. Large-scale effects from such changes on chemically produced tropospheric aerosols have not been systematically examined in past studies. We use a composition-climate model to investigate potential past and future impacts of changes in stratospheric ozone depleting substances (ODS) on tropospheric oxidants and sulfate aerosols. In most experiments, we find significant responses in tropospheric photolysis and oxidants, with small but significant effects on methane radiative forcing. The response of sulfate aerosols is sizeable when examining the effect of increasing future nitrous oxide (N2O) emissions. We also find that without the regulation of chlorofluorocarbons (CFCs) through the Montreal Protocol, sulfate aerosols could have increased by 2050 by a comparable amount to the decreases predicted due to relatively stringent sulfur emissions controls. The individual historical radiative forcings of CFCs and N2O through their indirect effects on methane (−22.6 mW m−2 for CFCs and −6.7 mW m−2 for N2O) and sulfate aerosols (−3.0 mW m−2 for CFCs and +6.5 mW m−2 for N2O when considering the direct aerosol effect) discussed here are non-negligible when compared to known historical ODS forcing. Our results stress the importance of accounting for stratosphere-troposphere, gas-aerosol and composition-climate interactions when investigating the effects of changing emissions on atmospheric composition and climate.

scholarly journals Contrasting Short- and Long-Term Projections of the Hydrological Cycle in the Southern Extratropics

2015 ◽  
Vol 28 (14) ◽  
pp. 5845-5856 ◽  
Author(s):  
Yutian Wu ◽  
Lorenzo M. Polvani
Keyword(s):  
Climate Model ◽  
Hydrological Cycle ◽  
Stratospheric Ozone ◽  
Practical Importance ◽  
Coupled Model ◽  
Montreal Protocol ◽  
Dry Zone ◽  
Near Term ◽  
Ozone Depleting Substances ◽  
Poleward Expansion

Abstract Analysis of model output from phase 5 of the Coupled Model Intercomparison Project (CMIP5) reveals that, in the zonal mean, the near-term projections of summertime changes of precipitation in the Southern Hemisphere (SH) subtropics are very widely scattered among the models. As a consequence, over the next 50 years, the CMIP5 multimodel mean projects no statistically significant trends in the SH subtropics in summer. This appears to be at odds with the widely reported, and robust, poleward expansion of the subtropical dry zones by the end of the twenty-first century. This discrepancy between the shorter- and longer-term projections in SH summer, as shown here, rests in the recovery of the ozone hole in the coming decades, as a consequence of the Montreal Protocol. This is explicitly demonstrated by analyzing model experiments with the Whole Atmosphere Community Climate Model, version 4 (WACCM4), a high-top model with interactive stratospheric chemistry, and coupled to land, ocean, and sea ice components. Contrasting WACCM4 integrations of the representative concentration pathway 4.5 with and without trends in surface concentrations of ozone-depleting substances allows for demonstrating that stratospheric ozone recovery will largely offset the induced “wet gets wetter and dry gets drier” projections and the accompanying poleward expansion of the subtropical dry zone in the SH. The lack of near-term statistically significant zonal-mean changes in the SH hydrological cycle during summer is of obvious practical importance for many parts of the world, and it might also have implications for the Southern Ocean and the Antarctic continent.

scholarly journals The Importance of the Montreal Protocol in Mitigating the Potential Intensity of Tropical Cyclones

2016 ◽  
Vol 29 (6) ◽  
pp. 2275-2289 ◽  
Author(s):  
Lorenzo M. Polvani ◽  
Suzana J. Camargo ◽  
Rolando R. Garcia
Keyword(s):  
Tropical Cyclones ◽  
Climate Model ◽  
Atmospheric Model ◽  
Montreal Protocol ◽  
Discernible Effect ◽  
Major Player ◽  
The World ◽  
Standard Scenario ◽  
Ozone Depleting Substances ◽  
The Impact

Abstract The impact of the Montreal Protocol on the potential intensity of tropical cyclones over the next 50 years is investigated with the Whole Atmosphere Community Climate Model (WACCM), a state-of-the-art, stratosphere-resolving atmospheric model, coupled to land, ocean, and sea ice components, with interactive stratospheric chemistry. An ensemble of WACCM runs from 2006 to 2065 forced with a standard future scenario is compared to a second ensemble in which ozone-depleting substances (ODS) are not regulated (the so-called World Avoided). It is found that by the year 2065, changes in the potential intensity of tropical cyclones in the World Avoided are nearly 3 times as large as for the standard scenario. The Montreal Protocol thus provides a strong mitigation of the adverse effects of intensifying tropical cyclones. The relative importance of warmer sea surface temperatures (ozone-depleting substances are important greenhouse gases) and cooler lower-stratospheric temperatures (accompanying the massive destruction of the ozone layer) is carefully examined. It is found that the former are largely responsible for the increase in potential intensity in the World Avoided, whereas temperatures above the 70-hPa level—which plunge by nearly 15 K in 2065 in the World Avoided—have no discernible effect on potential intensity. This finding suggests that the modest (compared to the World Avoided) tropical ozone depletion of recent decades has not been a major player in determining the intensity of tropical cyclones, and neither will ozone recovery be in the coming half century.

scholarly journals Linkages between ozone depleting substances, tropospheric oxidation and aerosols

2012 ◽  
Vol 12 (9) ◽  
pp. 25551-25572 ◽  
Author(s):  
A. Voulgarakis ◽  
D. T. Shindell ◽  
G. Faluvegi
Keyword(s):  
Radiative Forcing ◽  
Scale Effects ◽  
Stratospheric Ozone ◽  
Montreal Protocol ◽  
Tropospheric Chemistry ◽  
Atmospheric Composition ◽  
N2o Emissions ◽  
Sulfate Aerosols ◽  
Comparable Amount ◽  
Ozone Depleting Substances

Abstract. Coupling between the stratosphere and the troposphere allows changes in stratospheric ozone abundances to affect tropospheric chemistry. Large-scale effects from such changes on chemically produced tropospheric aerosols have not been systematically examined in past studies. We use a composition-climate model to investigate potential past and future impacts of changes in stratospheric Ozone Depleting Substances (ODS) on tropospheric oxidants and sulfate aerosols. In most experiments, we find significant responses in tropospheric photolysis and oxidants, with small but significant effects on methane radiative forcing. The response of sulfate aerosols is sizeable when examining the effect of increasing future nitrous oxide (N2O) emissions. We also find that without the regulation of chlorofluorocarbons (CFCs) through the Montreal Protocol, sulfate aerosols could have increased by 2050 by a comparable amount to the decreases predicted due to relatively stringent sulfur emissions controls. The historical radiative forcing of CFCs through their indirect effects on methane (−22.6 mW m−2) and sulfate aerosols (−3.0 mW m−2) discussed here is non-negligible when compared to known historical CFC forcing. Our results stress the importance of accounting for stratosphere-troposphere, gas-aerosol and composition-climate interactions when investigating the effects of changing emissions on atmospheric composition and climate.

scholarly journals Montreal Protocol benefits simulated with CCM SOCOL

2012 ◽  
Vol 12 (7) ◽  
pp. 17001-17030 ◽  
Author(s):  
T. Egorova ◽  
E. Rozanov ◽  
J. Gröbner ◽  
M. Hauser ◽  
W. Schmutz
Keyword(s):  
Uv Radiation ◽  
Ozone Depletion ◽  
Total Ozone ◽  
Climate Model ◽  
Montreal Protocol ◽  
Middle Latitudes ◽  
The World ◽  
Annual Total ◽  
Ozone Depleting Substances ◽  
Northern And Southern Hemispheres

Abstract. Ozone depletion is caused by the anthropogenic increase of halogen containing species in the atmosphere, which results in the enhancement of the concentration of reactive chlorine and bromine in the stratosphere. To reduce the influence of anthropogenic ozone-depleting substances (ODS), the Montreal Protocol was agreed by Governments in 1987, with several Amendments adopted later. In order to assess the benefits of the Montreal Protocol and its Amendments (MPA) on ozone and UV radiation, two different runs of the chemistry-climate model (CCM) SOCOL have been carried out. The first run was driven by the emission of ozone depleting substances (ODS) prescribed according to the restrictions of the Montreal Protocol and all its Amendments. For the second run we allow the ODS to grow by 3% annually. We find that the MPA would have saved up to 80% of the global annual total ozone by the end of the 21st century. Our calculations also show substantial changes in surface temperature and precipitations that could occur in the world without MPA implementations. To illustrate the changes in UV radiation at the surface and to emphasize certain features which can only be seen for some particular regions if the influence of the cloud cover changes is accounted for, we calculate geographical distribution of the erythemally weighted irradiance (Eery). For the no Montreal Protocol simulation Eery increases by factor of 4 to 16 between the 1970s and 2100. For the scenario including the Montreal Protocol it is found that UV radiation starts to decrease in 2000, with continuous decline of 5% to 10% at middle latitudes in the Northern and Southern hemispheres.

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

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.

scholarly journals Chemical and climatic drivers of radiative forcing due to changes in stratospheric and tropospheric ozone over the 21<sup>st</sup> century

2017 ◽  
Author(s):  
Antara Banerjee ◽  
Amanda C. Maycock ◽  
John A. Pyle
Keyword(s):  
Greenhouse Gas ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Radiative Forcings ◽  
Climatic Drivers ◽  
Ozone Precursor ◽  
Ozone Depleting Substances ◽  
Projected Changes

Abstract. The ozone radiative forcings (RFs) resulting from projected changes in climate, ozone-depleting substances (ODSs), non-methane ozone precursor emissions and methane between the years 2000 and 2100 are calculated using simulations from the UM-UKCA chemistry-climate model. Projected measures to improve air-quality through reductions in tropospheric ozone precursor emissions present a co-benefit for climate, with a net global mean ozone RF of −0.09 Wm−2. This is opposed by a positive ozone RF of 0.07 Wm−2 due to future decreases in ODSs, which is mainly driven by an increase in tropospheric ozone through stratosphere-to-troposphere exchange. An increase in methane abundance by more than a factor of two (as projected by the RCP8.5 scenario) is found to drive an ozone RF of 0.19 Wm−2, which would greatly outweigh the climate benefits of tropospheric non-methane ozone precursor reductions. A third of the ozone RF due to the projected increase in methane results from increases in stratospheric ozone. The sign of the ozone RF due to future changes in climate (including the radiative effects of greenhouse gas concentrations, sea surface temperatures and sea ice changes) is shown to be dependent on the greenhouse gas emissions pathway, with a positive RF (0.06 Wm−2) for RCP4.5 and a negative RF (−0.07 Wm−2) for the RCP8.5 scenario. This dependence arises from differences in the contribution to RF from stratospheric ozone changes.

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