The 1987 Montreal Protocol stands as a demonstration that sometimes when life is threatened, the world can come together and work together to save itself. The protocol sets the time-period for various ozone-depleting gases, the most famous being chlorofluorocarbons (CFCs). Despite occasional backsliding, the protocol has been held. The right-wing forecast of losses in the economy has largely proved unfounded, and the “ozone hole” at the South Pole in the spring has slowed, paused, and ultimately reversed its growth. Now we have learned that the effects of flow are going the same way.
Human-transmitted damage to the ozone layer has not only exposed us to dangerous ultraviolet radiation but has also caused changes in high-altitude winds, causing precipitation and loss of sea salinity. However, by 2000 the winds had stopped blowing and there were signs that they were returning to their former state. Meteorologists were unsure whether this recovery was a temporary loss, but now there is evidence that ozone-depleting gas emissions have been reduced, and there is a good chance that this will continue.
This does not necessarily mean that the consequences of all the holes will pass very quickly. In complex systems such as the atmosphere, a large shock can cause a change in an individual state that is not always reversed after the initial motivation has passed. Dr. Antara Banerjee of the University of Colorado led the way in determining whether changes in the Antarctic air represented a signal or sound.
Between the 1980s and 1990s, mid-latitude jet flow in the Southern Hemisphere shifted 2º toward the pole, and the tropical circulation known as the Hadley Cell became more prevalent. These effects and others were finally detected in the spring over Antarctica, ozone depletion, which allowed further penetration of ultraviolet light, warming the troposphere where we live and cooling the upper stratosphere. This may seem far from humane, but the Hadley Cell has reduced rainfall in semi-arid regions and endangered the livelihoods of millions of farmers fighting to harvest crops on marginal land.
In nature, Banerjee’s team reports that the three major weather-related trends in the hole closed in the 2000s. It has grown exponentially since then (the year 2000-2005 saw a return to all three which was almost perfect) deleted until 2010). But we now have a large number of samples to smooth short-term fluctuations and a break is obvious. It is less certain whether a bounce-back has begun, but the authors write that “the consequences of the Montreal Protocol for tropospheric circulation should be clearer in the future.”
The paper, however, warns that greenhouse gases often affect the same air system in the same way that ozone depletion and emissions can induce powerful enough shifts to overwhelm any recovery. “The answer will depend on the CO2 emissions trajectory,” they wrote. Just like everything else.
