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"ozone depletion"
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Stratospheric ozone depletion due to nitrous oxide: influences of other gases
The effects of anthropogenic emissions of nitrous oxide (N2O), carbon dioxide (CO2), methane (CH4) and the halocarbons on stratospheric ozone (O3) over the twentieth and twenty-first centuries are isolated using a chemical model of the stratosphere. The future evolution of ozone will depend on each of these gases, with N2O and CO2 probably playing the dominant roles as halocarbons return towards pre-industrial levels. There are nonlinear interactions between these gases that preclude unambiguously separating their effect on ozone. For example, the CH4 increase during the twentieth century reduced the ozone losses owing to halocarbon increases, and the N2O chemical destruction of O3 is buffered by CO2 thermal effects in the middle stratosphere (by approx. 20% for the IPCC A1B/WMO A1 scenario over the time period 1900–2100). Nonetheless, N2O is expected to continue to be the largest anthropogenic emission of an O3-destroying compound in the foreseeable future. Reductions in anthropogenic N2O emissions provide a larger opportunity for reduction in future O3 depletion than any of the remaining uncontrolled halocarbon emissions. It is also shown that 1980 levels of O3 were affected by halocarbons, N2O, CO2 and CH4, and thus may not be a good choice of a benchmark of O3 recovery.
Journal Article
Mario and the hole in the sky : how a chemist saved our planet
\"The true story of how Mexican-American scientist Mario Molina helped solve the ozone crisis of the 1980s and went on to become a Nobel laureate and a recipient of the Presidential Medal of Freedom. His inspiring story gives hope in the fight against global warming\"--Publisher's description.
BOOK
Chemistry Contribution to Stratospheric Ozone Depletion After the Unprecedented Water‐Rich Hunga Tonga Eruption
Following the Hunga Tonga–Hunga Ha'apai (HTHH) eruption in January 2022, stratospheric ozone depletion was observed at Southern Hemisphere mid‐latitudes and over Antarctica during the 2022 austral wintertime and springtime, respectively. The eruption injected sulfur dioxide and unprecedented amounts of water vapor into the stratosphere. This work examines the chemistry contribution of the volcanic materials to ozone depletion using chemistry‐climate model simulations with nudged meteorology. Simulated 2022 ozone and nitrogen oxide (NOx = NO + NO2) anomalies show good agreement with satellite observations. We find that chemistry yields up to 4% ozone destruction at mid‐latitudes near ∼70 hPa in August and up to 20% ozone destruction over Antarctica near ∼80 hPa in October. Most of the ozone depletion is attributed to internal variability and dynamical changes forced by the eruption. Both the modeling and observations show a significant NOx reduction associated with the HTHH aerosol plume, indicating enhanced dinitrogen pentoxide hydrolysis on sulfate aerosol. Plain Language Summary The January 2022 eruption of the Hunga Tonga‐Hunga Ha'apai underwater volcano injected a large amount of water vapor (H2O) and moderate amounts of sulfur dioxide (SO2) into the stratosphere. Stratospheric ozone depletion was observed following the eruption at Southern Hemisphere (SH) mid‐latitudes and over Antarctica during the 2022 austral wintertime and springtime, respectively. The ozone layer in the stratosphere protects both people and the biosphere by absorbing harmful solar ultraviolet radiation. We use computer simulation to examine the impacts of chemical processes on the ozone layer from the volcanic materials. We find that chemistry results in 4% and 20% of the ozone loss at SH mid‐latitudes near 70 hPa in August and Antarctica around 80 hPa in October respectively. Most of the ozone changes are due to transport and dynamical processes from internal variability in the climate system and a forced response by the HTHH eruption. Key Points Chemistry yields 4% and 20% ozone depletion in the lower stratosphere at mid‐latitudes and Antarctica in August and October, respectively The majority of ozone depletion is ascribed to internal variability and dynamical changes induced by the eruption HTHH aerosol plume is associated with notable NOx reduction, indicating enhanced dinitrogen pentoxide hydrolysis on sulfate aerosol
Journal Article
The Montreal Protocol protects the terrestrial carbon sink
The control of the production of ozone-depleting substances through the Montreal Protocol means that the stratospheric ozone layer is recovering
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and that consequent increases in harmful surface ultraviolet radiation are being avoided
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,
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. The Montreal Protocol has co-benefits for climate change mitigation, because ozone-depleting substances are potent greenhouse gases
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–
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. The avoided ultraviolet radiation and climate change also have co-benefits for plants and their capacity to store carbon through photosynthesis
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, but this has not previously been investigated. Here, using a modelling framework that couples ozone depletion, climate change, damage to plants by ultraviolet radiation and the carbon cycle, we explore the benefits of avoided increases in ultraviolet radiation and changes in climate on the terrestrial biosphere and its capacity as a carbon sink. Considering a range of strengths for the effect of ultraviolet radiation on plant growth
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–
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, we estimate that there could have been 325–690 billion tonnes less carbon held in plants and soils by the end of this century (2080–2099) without the Montreal Protocol (as compared to climate projections with controls on ozone-depleting substances). This change could have resulted in an additional 115–235 parts per million of atmospheric carbon dioxide, which might have led to additional warming of global-mean surface temperature by 0.50–1.0 degrees. Our findings suggest that the Montreal Protocol may also be helping to mitigate climate change through avoided decreases in the land carbon sink.
Modelling suggests that the Montreal Protocol may be mitigating climate change by protecting the land carbon sink, as well as by protecting the ozone layer and reducing greenhouse gas emissions.
Journal Article
Discerning experts : the practices of scientific assessment for environmental policy
\"Discerning Experts assesses the assessments that many governments rely on to help guide environmental policy and action. Through their close look at environmental assessments involving acid rain, ozone depletion, and sea level rise, the authors explore how experts deliberate and decide on the scientific facts about problems like climate change. They also seek to understand how the scientists involved make the judgments they do, how the organization and management of assessment activities affects those judgments, and how expertise is identified and constructed.\"--cover
Book
Approximate Near-Real-Time Assessment of Some Characteristic Parameters of the Spring Ozone Depletion over Antarctica Using Ground-Based Measurements
The strong Antarctic vortex plays a crucial role in forming an expansive region with significant stratospheric ozone depletion during austral spring, commonly referred to as the Antarctic “ozone hole”. This study examines daily ozone column behavior during this phenomenon using ERA5 reanalysis data and ground-based observations from 10 Antarctic stations collected between September and December from 2008 to 2022. A preliminary analysis of these datasets revealed smoothly varying patterns with quasi-uniform gradients in the ozone distribution within the ozone hole. This observation led to the hypothesis that average ozone columns over zones, defined as concentric areas around the South Pole, can be estimated using mean values of the measurements derived from station observations. This study aims to evaluate the validity of this hypothesis. The results indicate that the mean ozone levels calculated from daily measurements at two stations—Belgrano and Dome Concordia, or Belgrano and Arrival Heights—provide a reliable approximation of the average ozone levels over the zone spanning 70°S to 90°S. Including additional stations extended the zone of reliable approximation northward to 58°S. The approximation error was estimated to range from 5% to 7% at 1σ and from 6% to 8% at the 10th–90th percentile levels. Furthermore, the geographical distribution of the stations enabled a schematic reconstruction of the ozone hole’s position and shape. On the other hand, the high frequency of ground-based measurements contributed to studying the ozone hole variability in both the inner area and edges on an hourly time scale. These findings have practical implications for the near-real-time monitoring of ozone hole development, along with satellite observations, considering ground-based measurements as a source of information about ozone layer in the South Pole region. The results also suggest the possible role of observations from the ground in the analyses of pre-satellite-era hole behavior. Additionally, this study found a high degree of consistency between ground-based measurements and corresponding ERA5 reanalysis data, further supporting the reliability of the observations.
Journal Article
An unexpected and persistent increase in global emissions of ozone-depleting CFC-11
The Montreal Protocol was designed to protect the stratospheric ozone layer by enabling reductions in the abundance of ozone-depleting substances such as chlorofluorocarbons (CFCs) in the atmosphere
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–
3
. The reduction in the atmospheric concentration of trichlorofluoromethane (CFC-11) has made the second-largest contribution to the decline in the total atmospheric concentration of ozone-depleting chlorine since the 1990s
1
. However, CFC-11 still contributes one-quarter of all chlorine reaching the stratosphere, and a timely recovery of the stratospheric ozone layer depends on a sustained decline in CFC-11 concentrations
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. Here we show that the rate of decline of atmospheric CFC-11 concentrations observed at remote measurement sites was constant from 2002 to 2012, and then slowed by about 50 per cent after 2012. The observed slowdown in the decline of CFC-11 concentration was concurrent with a 50 per cent increase in the mean concentration difference observed between the Northern and Southern Hemispheres, and also with the emergence of strong correlations at the Mauna Loa Observatory between concentrations of CFC-11 and other chemicals associated with anthropogenic emissions. A simple model analysis of our findings suggests an increase in CFC-11 emissions of 13 ± 5 gigagrams per year (25 ± 13 per cent) since 2012, despite reported production being close to zero
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since 2006. Our three-dimensional model simulations confirm the increase in CFC-11 emissions, but indicate that this increase may have been as much as 50 per cent smaller as a result of changes in stratospheric processes or dynamics. The increase in emission of CFC-11 appears unrelated to past production; this suggests unreported new production, which is inconsistent with the Montreal Protocol agreement to phase out global CFC production by 2010.
Atmospheric CFC-11 concentrations have been declining less rapidly since 2012; evidence suggests that this finding is explained by an increase in the emission of CFC-11during these years.
Journal Article
Anthropogenic forcing on the Hadley circulation in CMIP5 simulations
Poleward expansion of the Hadley circulation has been an important topic in climate change studies in the past few years, and one of the critically important issues is how it is related to anthropogenic forcings. Using simulations from the coupled model intercomparison projection phase 5 (CMIP5), we study influences of anthropogenic forcings on the width and strength of the Hadley circulation. It is found that significant poleward expansion of the Hadley circulation can be reproduced in CMIP5 historical all-forcing simulations although the magnitude of trends is much weaker than observations. Simulations with individual forcings demonstrate that among three major types of anthropogenic forcings, increasing greenhouse gases (GHGs) and stratospheric ozone depletion all cause poleward expansion of the Hadley circulation, whereas anthropogenic aerosols do not have significant influences on the Hadley circulation. Increasing GHGs cause significant poleward expansion in both hemispheres, with the largest widening of the northern cell in boreal autumn. Stratospheric ozone depletion forces significant poleward expansion of the Hadley circulation for the southern cell in austral spring and summer and for the northern cell in boreal spring. In CMIP5 projection simulations for the twenty-first century, the magnitude of poleward expansion of the Hadley circulation increases with GHG forcing. On the other hand, ozone recovery competes with increasing GHGs in determining the width of the Hadley circulation, especially in austral summer. In both historical and projection simulations, the strength of the Hadley circulation shows significant weakening in winter in both hemispheres.
Journal Article