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- The ozone will be healed by 2020 Kerr 11
- The ozone is making major steps toward major recovery Shanklin 10
Ozone—UQThe ozone is beginning to heal Crow 11 James Mitchell Crow, Assistant Editor for RSC Magazine Published online 16 May 2011 First signs of ozone-hole recovery spotted, http://www.nature.com/news/2011/110516/full/news.2011.293.html The average size of the Antarctic ozone hole in October 2010. Its recovery has so far been masked by annual fluctuations. The hole in the ozone layer over Antarctica is starting to heal, say researchers in Australia. The team is the first to detect a recovery in baseline average springtime ozone levels in the region, 22 years after the Montreal Protocol to ban chlorofluorocarbons (CFCs) and related ozone-destroying chemicals came into force. Each spring, those chlorine- and bromine-releasing chemicals eat a hole in the ozone layer above the Antarctic. Thanks to the Montreal agreement, levels of anthropogenic ozone depleters detected in the region's stratosphere have been falling since around the turn of the millennium. However, detecting any corresponding ozone recovery has been difficult. That difficulty is down to significant natural variations in average Antarctic stratospheric springtime ozone levels from year to year, which mean that the hole can be small one year and large the next. Scientists did not expect to be able to detect the gradual recovery of ozone for decades, masked as it is by these dramatic swings. However, Murry Salby, an environmental scientist at Macquarie University in Sydney, Australia, and his colleagues have now shown how this annual fluctuation can be accounted for — and so removed from the data. They are left with the underlying systematic change in Antarctic ozone levels. Salby's calculations reveal that the levels are now rising; the findings are published in Geophysical Research Letters1. The team's breakthrough was in showing that annual swings in average springtime ozone levels are linked to changes in a particular pattern of stratospheric weather known as dynamical forcing. In years in which this phenomenon is strong during the winter, more cold air is trapped above the pole. As a result, there are more ice crystals in the atmosphere. These crystals form the surface on which chlorine destroys ozone, catalysed by sunlight returning to the Antarctic during the spring. "I think this is the first convincing observationally-derived evidence of the ozone rebound," says Adrian McDonald, an atmospheric scientist at the University of Canterbury in Christchurch, New Zealand. "It's the first where the statistical significance is high enough, and you can see the pattern well enough, that you feel comfortable in believing it." Salby's results reveal a fast decline in ozone levels until the late 1990s, then a slow rebound that closely matches what theoretical calculations had predicted, says David Karoly, a climate scientist at the University of Melbourne, Australia. "It is the sort of result that was expected, but is the first to provide detection of an increase in Antarctic ozone levels," he says. Adding weight to Salby's argument, the increase in ozone levels revealed by the calculations closely mirror the decrease in the levels of anthropogenic chlorine in the region. "For now, they agree pretty well," says Salby. "My feeling is that as time goes on we will start to see other influences on the systematic evolution of ozone level beside chlorine." One such influence is likely to be the increasing concentration of carbon dioxide in the atmosphere. Salby's data reveal that average springtime Antarctic ozone levels have already recovered by 15% since the late 1990s. However, projecting forward, natural weather-related fluctuations mean that even as late as 2085, ozone will still drop below 1980 levels for at least one year in every ten. A complicating factor in that prediction is the influence of climate change, says Karoly. "Even when CFCs are removed, ozone levels will be different in the future than they were in the 1960s, because of changes in temperature in the stratosphere." The ozone will be healed by 2020 Kerr 11 Richard A. Kerr ( Writer for Science Magazine) Science 8 April First Detection of Ozone Hole Recovery Claimed, http://www.sciencemag.org/content/332/6026/160.full The feel-good environment story of recent decades—the recovery of the so-called ozone hole—may be passing a major milestone far ahead of schedule. Every austral spring, an ominous “hole” appears in stratospheric ozone over Antarctica. In 1989, international regulations began restricting emissions of ozone-destroying chemicals, such as chlorine-containing refrigerants and propellants. The restrictions quickly capped and then began steadily reducing atmospheric concentrations of those dangerous chemicals. Although ozone-destroying chemicals have been in decline for a decade now, researchers have long projected that they will not glimpse the first signs that the hole is healing until well past 2020. But for the first time, a group of researchers claims they can already see the ozone hole slowly recovering. Many others, however, say the paper, now in press in Geophysical Research Letters (GRL), leaves out critical information needed to clinch the case. No one had been expecting to discern the recovery quite so soon. Scientists thought large, wholly natural, year-to-year variations in Antarctic ozone would obscure any small upward trend. Those natural ozone variations can be traced back through physical and chemical changes in the atmosphere to natural changes in atmospheric circulation. But no one had been able to take those circulation changes into account accurately enough to reveal the underlying ozone recovery. Meteorologist Murry Salby of Macquarie University in Sydney, Australia, and his Australian colleagues think they have nailed down the natural influences on the hole's ozone. In their GRL paper, they consider how much of the observed polar ozone variation each spring could be accounted for by changes in two kinds of atmospheric circulation that ultimately influence the amount of ozone destroyed in making the hole each spring. Taken together, the two observed that circulation changes accounted for “virtually all” of the year-to-year changes in springtime Antarctic ozone, Salby and colleagues write. Subtracting their estimate of the natural changes in ozone from actual changes, the group finds “a clear upward trend since the late 1990s” in the hole's ozone that represents “a systematic rebound.” Over the past decade, the rebound has amounted to about 15%, they estimate. “It's a small trend, but it's all we've been waiting for,” says meteorologist Lorenzo Polvani of Columbia University. “Now we're actually seeing it.” The ozone is making major steps toward major recovery Shanklin 10 Jonathan Shanklin, British Antarctic Survey Member, 2010, The Ozone Layer Fact Sheet, http://www.theozonehole.com/fact.htm Over the last 50 years we have introduced chemicals into the atmosphere that are capable of destroying ozone through photochemical processes. Chloro-fluoro-carbons (CFCs) are widely known, but there are also other ozone depleting substances such as halons (bromo-fluoro-carbons) and methyl bromide. In certain circumstances the chlorine or bromine from these substances can react with ozone to turn it back into oxygen. In most parts of the world the reactions are very slow and there is little damage to the ozone layer, however over the Antarctic a dramatic hole opens in the ozone layer every spring and fills in again by mid-summer. This is created by the unusual atmospheric conditions that exist during the Antarctic winter. An international treaty, the Montreal Protocol, has been drawn up to control the release of ozone depleting chemicals into the atmosphere. This treaty is clearly working, and the amount of these chemicals in air near the surface is beginning to decline. The chemicals are however so stable that it will take a long time before they drop to the levels that existed 50 years ago and it is likely that we will see an annual ozone hole over Antarctica for many decades to come. The answer is essentially 'because of the weather in the ozone layer'. In order for rapid ozone destruction to happen, clouds (known as PSCs, Stratospheric Clouds Mother of Pearl or Nacreous Clouds) have to form in the ozone layer. In these clouds surface chemistry takes place. This converts chlorine or bromine (from CFCs and other ozone depleting chemicals) into an active form, so that when there is sunlight, ozone is rapidly destroyed. Without the clouds, there is little or no ozone destruction. Only during the Antarctic winter does the atmosphere get cold enough for these clouds to form widely through the centre of the ozone layer. Elsewhere the atmosphere is just too warm and no clouds form. The northern and southern hemispheres have different 'weather' in the ozone layer, and the net result is that the temperature of the Arctic ozone layer during winter is normally some ten degrees warmer than that of the Antarctic. This means that such clouds are rare, but sometimes the 'weather' is colder than normal and they do form. Under these circumstances significant ozone depletion can take place over the Arctic, but it is usually for a much shorter period of time and covers a smaller area than in the Antarctic. Some reports in the media suggest that the ozone layer over Antarctica is now recovering. This message is a little confused. Recent measurements at surface monitoring stations show that the loading of ozone destroying chemicals at the surface has been dropping since about 1994 and is now about 6% down on that peak. The stratosphere lags behind the surface by several years and the loading of ozone depleting chemicals in the ozone layer is at or near the peak. Satellite measurements show that the rate of decline in ozone amount in the upper stratosphere is slowing, however the total ozone amount is still declining. The small size of the 2002 ozone hole was nothing to do with any reduction in ozone depleting chemicals and it will be a decade or more before we can unambiguously say that the ozone hole is recovering. This assumes that the decline in ozone depleting chemicals continues and that there are no other perturbations to the ozone layer, such as might be caused by a massive volcanic eruption or Tunguska like event. It will be the middle of this century or beyond before the ozone hole ceases to appear over Antarctica. What we saw in 2002 is just one extreme in the natural range of variation in the polar stratosphere and is the equivalent of an extreme in 'stratospheric weather'. By contrast the 'weather' in 2003 moved to the opposite extreme and we saw one of the largest ozone holes on record. 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