Substream - sub_gw_impact_ozone

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  2. 17-02-2011 eco nws - global warming - impact - ozone layer - Ozone Layer�s Future Linked Strongly to Changes in Climate, Study Finds - ScienceDaily (Feb. 17, 2011) � The ozone layer -- the thin atmospheric band high-up in the stratosphere that protects living things on Earth from the sun's harmful ultraviolet rays, not to be confused with damaging ozone pollution close to the ground -- faces potential new challenges even as it continues its recovery from earlier damage, according to a recently released international science assessment. The report, prepared by the Scientific Assessment Panel of the U.N. Montreal Protocol on Substances that Deplete the Ozone Layer, also presents stronger evidence that links changes in stratospheric ozone and Earth's climate. The report finds that over the past decade, global ozone levels, and ozone levels in the Arctic and Antarctic regions are at a turnaround point -- no longer decreasing but not yet increasing. The abundances of ozone-depleting substances in the atmosphere are responding as expected to the controls of the Montreal Protocol, with many now declining in both the lower and upper atmosphere. By successfully controlling the emissions of ozone-depleting substances, the Montreal Protocol also has been beneficial for the climate, because many of these substances are heat trapping, or greenhouse, gases that are linked to Earth's warming. "The Montreal Protocol has succeeded in protecting the ozone layer from much higher levels of depletion," said A.R. Ravishankara, director of NOAA's Chemical Sciences Division and co-chair of the Scientific Assessment Panel that produced the report. "But the ozone layer will increasingly be influenced by other factors related to the changing climate." For example, climate change alters the atmosphere's temperature and circulation patterns, which in turn affect the processes that deplete the ozone layer. One projected outcome of this relationship is that ozone in the Arctic, where the most severe changes in climate are being observed, is projected to be more sensitive to climate changes than ozone in the Antarctic, where climate change is relatively less of an influence on the ozone layer. Effects also work in reverse. Changes in the ozone layer have been linked to observed shifts in seasonal surface winds over the Southern Hemisphere, contributing to the Antarctic Peninsula warming and the high plateau cooling. The Antarctic ozone hole was discovered in 1985. Soon after, scientists established that the recurring springtime ozone hole was caused by human-made substances such as chlorofluorocarbons, or CFCs, used in refrigeration and halons used in fire extinguishers. The findings became a "science success story" as governments recognized the need for measures to reduce the production and consumption of a number of CFCs, halons and other ozone-depleting substances. The Montreal Protocol on Substances that Deplete the Ozone Layer was adopted in 1987 and came into force in 1989. It was designed so that the schedules for phasing out ozone-depleting substances could be revised based on periodic scientific and technological assessments, be amended or adjusted to introduce other kinds of control measures, and to add new controlled substances to the list. The 2010 scientific assessment just released provides information needed by the Protocol's decision-makers during the coming few years as they consider possible further actions to protect the ozone layer. A return to pre-1980 levels of ozone is expected around mid-century in mid-latitude regions and the Arctic, with recovery in the Antarctic expected to follow later this century, according to the assessment. The ozone layer's continued protection depends on future adherence to the provisions of the Montreal Protocol, as well as potential new influences, such as possible unintended consequences of proposals to deliberately add compounds to the atmosphere to counteract warming due to heat-trapping gases. "The Montreal Protocol is doing what it was designed to do and we are seeing less of the ozone-depleting substances covered by the agreement," said Ravishankara. "This has protected the ozone layer. But the atmosphere and climate are changing, so the ozone layer will not exactly retrace its steps." NOAA scientists and colleagues contributed findings that were critical to the assessment report. Namely, they led studies that determined the cause of the Antarctic ozone hole and elucidated the processes involved in ozone depletion in other regions of the globe. Teams have also tracked the state of the ozone layer and the abundances of ozone-depleting substances in the atmosphere, and modeled the past and projected future state of the ozone layer. The 2010 assessment was conducted under the auspices of the United Nations Environment Programme and the World Meteorological Organization. It involved more than 300 international scientists as authors and reviewers. The full report is posted on the UNEP website:

  3. 25-04-2011 eco nws - global warming - impact - ozone layer - Ozone Hole Linked to Climate Change All the Way to the Equator - ScienceDaily (Apr. 25, 2011) � In a study to be published in the April 21st issue of Science, researchers at Columbia University's School of Engineering and Applied Science report their findings that the ozone hole, which is located over the South Pole, has affected the entire circulation of the Southern Hemisphere all the way to the equator. While previous work has shown that the ozone hole is changing the atmospheric flow in the high latitudes, the new Columbia Engineering paper demonstrates that the ozone hole is able to influence the tropical circulation and increase rainfall at low latitudes in the Southern Hemisphere. This is the first time that ozone depletion, an upper atmospheric phenomenon confined to the polar regions, has been linked to climate change from the Pole to the equator. "The ozone hole is not even mentioned in the summary for policymakers issued with the last IPCC report," noted Lorenzo M. Polvani, Professor of Applied Mathematics and of Earth & Environmental Sciences, Senior Research Scientist at the Lamont-Doherty Earth Observatory, and co-author of the paper. "We show in this study that it has large and far-reaching impacts. The ozone hole is a big player in the climate system!" "It's really amazing that the ozone hole, located so high up in the atmosphere over Antarctica, can have an impact all the way to the tropics and affect rainfall there -- it's just like a domino effect," said Sarah Kang, Postdoctoral Research Scientist in Columbia Engineering's Department of Applied Physics and Applied Mathematics and lead author of the paper. The ozone hole is now widely believed to have been the dominant agent of atmospheric circulation changes in the Southern Hemisphere in the last half century. This means, according to Polvani and Kang, that international agreements about mitigating climate change cannot be confined to dealing with carbon alone -- ozone needs to be considered, too. "This could be a real game-changer," Polvani added. Located in Earth's stratosphere, just above the troposphere (which begins on Earth's surface), the ozone layer absorbs most of the Sun's harmful ultraviolet rays. Over the last half-century, widespread use of humanmade compounds, especially household and commercial aerosols containing chlorofluorocarbons (CFCs), has significantly and rapidly broken down the ozone layer, to a point where a hole in the Antarctic ozone layer was discovered in the mid 1980s. Thanks to the 1989 Montreal Protocol, now signed by 196 countries, global CFC production has been phased out. As a result, scientists have observed over the past decade that ozone depletion has largely halted and they now expect it to fully reverse, and the ozone hole to close by midcentury. But, as Polvani has said, "While the ozone hole has been considered as a solved problem, we're now finding it has caused a great deal of the climate change that's been observed." So, even though CFCs are no longer being added to the atmosphere, and the ozone layer will recover in the coming decades, the closing of the ozone hole will have a considerable impact on climate. This shows that through international treaties such as the Montreal Protocol, which has been called the single most successful international agreement to date, human beings are able to make changes to the climate system. Together with colleagues at the Canadian Centre for Climate Modelling and Analysis in Victoria, BC, Kang and Polvani used two different state-of-the-art climate models to show the ozone hole effect. They first calculated the atmospheric changes in the models produced by creating an ozone hole. They then compared these changes with the ones that have been observed in the last few decades: the close agreement between the models and the observations shows that ozone has likely been responsible for the observed changes in Southern Hemisphere. This important new finding was made possible by the international collaboration of the Columbia University scientists with Canadian colleagues. Model results pertaining to rainfall are notoriously difficult to calculate with climate models, and a single model is usually not sufficient to establish credible results. By joining hands and comparing results from two independent models, the scientists obtained solid results. Kang and Polvani plan next to study extreme precipitation events, which are associated with major floods, mudslides, etc. "We really want to know," said Kang, "if and how the closing of the ozone hole will affect these." This study was funded by a grant from the National Science Foundation to Columbia University.