Montreal Protocol hailed for shrinking ozone hole

Worldwide effort to slow depletion of ozone layer

American scientists say they now have “direct proof” that links the shrinking ozone hole over the Antarctic to the Montreal Protocol, the worldwide effort started in the 1980s to ban production of ozone-depleting chemicals.

“This is very encouraging news,” said Kimberly Strong, a professor of atmospheric physics at the University of Toronto. “This study provides clear evidence that the Montreal Protocol is working.”

Discovery of the hole in 1985 elevated concerns about damage to the ozone layer, the invisible barrier in the Earth’s stratosphere that protects humans from the sun’s harmful ultraviolet rays.

News reports at the time warned that ozone depletion could raise temperatures, damage farm crops and lead to increased rates of skin cancer.

Back then, “everybody knew about the ozone problem. It was talked about continually, at dinner parties, in the newspapers — rather like global warming is today,” recalled David Tarasick, a federal scientist at Environment and Climate Change Canada.

Man-made chemicals, called chlorofluorocarbons, were identified as the major culprit behind the weakening ozone layer. At the time, CFCs were widely used as coolants in automobile air conditioners and refrigerators, and to make plastic foam in home insulation and disposable food containers.

In 1987, in what was heralded as a major diplomatic feat, the world’s countries came together in Canada to sign the Montreal Protocol, an international treaty aimed at gradually eliminating the production of ozonedepleting substances.

“Banning them was a global undertaking that seemed impossible at first,” Tarasick said. “The Montreal Protocol stands as a tremendously encouraging example of what people can accomplish with determination — and solid science to back them up.”

Thirty years later, scientists with the U.S. National Aeronautics and Space Administration (NASA) say satellite observations show levels of chlorine — the component of CFCs that damage the ozone — have dropped inside the Antarctic ozone hole, resulting in a 20-percent reduction in ozone depletion during the Antarctic winter compared to 12 years ago.

“The Montreal Protocol has been a great success at banning the production of ozone-depleting substances,” said Susan Strahan, a NASA atmospheric scientist in a video posted on the agency’s website. “We see for the first time chlorine levels are definitely going down and ozone levels are responding to it.”

The U.S. National Oceanic and Atmospheric Administration (NOAA) previously reported that the ozone hole, which forms over the Antarctic every September, grew to only 19.6 million square kilometres in 2017 (about 2.5 times the size of the United States), the smallest it had been in 30 years.

Had the world not intervened and allowed CFC production to continue unabated, some projections have suggested 17 per cent of the world’s ozone would have been destroyed by 2020 and 67 per cent by 2065. Skin cancer rates would have “soared.”

“It’s a nice reminder that the danger was not oversold — it really was a big problem — but we solved it,” Tarasick said.

Because CFCs have long shelf lives and can linger in the atmosphere for a long time, the healing of the Antarctic ozone layer will still likely take decades, scientists say. Scientists also continue to monitor the ozone layer over the Arctic, which saw record levels of depletion in 2011. Since then, however, the annual losses have not been as dramatic.

“We still need to keep an eye on the ozone layer, as surprises can happen as they have in the past,” Strong said, “but we are generally doing the right thing with the Montreal Protocol and its amendments.”

A key “next step,” Strong said, will be to phase out of some of the compounds that have replaced CFCs, known as hydrofluorocarbons. While HFCs do no harm to the ozone layer, they act as potent greenhouse gases, which contribute to global warming.

If left unchecked, scientists say, HFCs could account for 10 per cent of global greenhouse gas emissions by 2050.

In November, Catherine McKenna, the federal environment minister, announced that Canada had ratified an amendment to the Montreal Protocol that aims to phase out HFCs.

Under new federal regulations, Canada’s consumption of HFCs is expected to drop by 85 per cent by 2036.