In 1987, world leaders defied industry lobbying, science denial and predictions of economic disaster to sign the Montreal Protocol, phasing out a number of gasses that were damaging the ozone layer. Now, a new study reveals that without the Protocol, the ozone layer would have been much worse than previously thought. The results have been published in Nature Communications.
"Ozone depletion in the polar regions depends on meteorology, especially the occurrence of cold temperatures at about 20km [12.4 mile] altitude - colder temperatures cause more loss,” said Professor Martyn Chipperfield of the University of Leeds. “Other studies which have assessed the importance of the Montreal Protocol have used models to predict atmospheric winds and temperatures and have looked a few decades into the future. The prediction of winds and temperatures in these models are uncertain, and probably underestimate the extent of cold winters.”
Chipperfield used satellite observations of recent weather to give "a more accurate simulation of the conditions for polar ozone loss." He found that without the phaseout, the spring Antarctic ozone hole would have been 40% larger in 2013 than it was and that “the decline over northern hemisphere middle latitudes would have continued, more than doubling to ~15% by 2013.” Ultraviolet radiation would have been “8–12% in Australia and New Zealand and 14% in the United Kingdom.”
The Arctic was exceptionally cold in the winter of 2010/11. "We could see that previous models used to predict the impact of the Montreal Protocol in the future would not have predicted such extreme events and we wondered how much worse things could have been if the Montreal Protocol had not been in place," Chipperfield said. Had depleting chemicals continued unchecked, such a winter would have produced a hole resembling those seen over the Antarctic, but affecting far more people.
A comparison of the Arctic in spring 2011 as it was (right) and would have been (left) without the Montreal Protocol. Credit Chipperfield et al.
“For every 5% increase in sun-burning UV radiation, the increase in skin cancer incidence would be 15% and 8% for squamous and basal cell carcinomas, respectively,” Chipperfield told IFLScience. “The data for the more serious melanoma rates is uncertain.” Meanwhile, Antarctic food webs have been suffering severe effects from increased UV light, and the additional radiation Chipperfield's team have modeled might well have produced total ecosystem collapses.
Ozone depleting gasses, molecule for molecule, have warming effects far beyond those of carbon dioxide. Chipperfield points to a United Nations Environment Program study that found the climate benefits from the Montreal Protocol have been five to six times those aimed for in the Kyoto Treaty.
“The additional climate change would have caused a small cooling of the stratosphere on average, [but] it is not clear that...an absence of the Protocol would have led to more extreme cold Arctic winters,” Chipperfield added.
He points to evidence that short-lived industrial gasses such as dichloromethane (CH2Cl2) are reaching the stratosphere and interfering with the ozone, with pressure to add them to the list of chemicals banned under the Protocol.