2015-04-28. Ozone Hole to Remain Large During Cold Years.

posted May 2, 2015, 7:53 PM by Alan Gould
By Eric Betz, EOS Earth and Space Science News. For GSS Ozone chapter 9. Excerpt: Despite the Montreal Protocol's success, it will take years of observations to be sure that regulations are allowing the ozone hole to recover. ...In 1987, the nations of the world negotiated the Montreal Protocol to stop the harmful emissions of CFCs. The hole quit growing by the mid-1990s, but recovery of the protective shield has been slow because many ozone-depleting substances can last in the atmosphere for 50 and even 100 years. Scientists project that the hole will not vanish until around 2070. However, conclusively tying the international regulations to ozone recovery is not straightforward. While CFCs are no longer emitted, scientists calculate that the slow destruction of CFCs already in the atmosphere causes chlorine to decline each year by roughly 20 parts per trillion (ppt), or about 0.5%. However, Earth-orbiting satellites indicate that the natural variability of chlorine levels over Antarctica is up to 10 times larger than the expected annual decline. ...According to Strahan et al., it will take a decade of chlorine declines to be certain the Montreal Protocol has caused the ozone hole to shrink. Low temperatures in the Antarctic stratosphere currently play the largest role in determining the size of the ozone hole. In 2006, the combination of very low temperatures and high chlorine levels produced the largest ozone hole ever. By 2040, the authors expect that chlorine levels will have fallen enough that the ozone hole will be smaller than it is today even during a very cold year. The authors say it is unlikely any future ozone hole will grow to 2006 levels.... https://eos.org/research-spotlights/ozone-hole-to-remain-large-during-cold-years
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