Ozone layer treaty helped limit climate change

29 September 2008

Climate change would be an even bigger problem if governments hadn't taken the action they did to combat the ozone hole, according to new research.

Ozone hole extent

A paper published in Geophysical Research Letters says an international protocol aimed at preventing further damage to the ozone layer also made a big impact on climate change.

Its authors conclude that the protocol "provided an enormous benefit not only to the stability of the stratospheric ozone layer but also to surface climate."

British Antarctic Survey scientists were the first to notice the problem of ozone depletion.

"It's a very good thing that we didn't keep emitting CFCs at early 1980s levels - doing so would have had a substantial climate impact," says John Pyle, professor of physical chemistry at Cambridge University and co-director of the National Centre for Atmospheric Science, who co-authored the paper.

"For example, summer arctic sea-ice has become extremely low in recent years, and the pattern of heating in the region that our models predict would have made this far worse," he adds.

The Montreal Protocol has had a huge impact in terms of climate change, over and above the benefits that have come out of Kyoto.

- Professor John Pyle

The 1987 Montreal Protocol was a landmark international agreement to curb emissions of chlorofluorocarbons, or CFCs - chemicals that were until then commonly used as refrigerants and solvents. CFCs were found to be damaging the ozone layer in the upper atmosphere that shields the Earth from the worst of the sun's ultraviolet (UV) radiation.

Levels of chlorine in the atmosphere, a consequence of CFC emissions, are now around 3·5 parts per billion by volume. Without the protocol, scientists say that figure could easily have increased to around 9ppbv by 2030.

As well as more harmful UV rays reaching the poles, a larger ozone hole would have caused major climate change in many parts of the world because of the complex links between levels of ozone high in the atmosphere and temperatures at ground level.

Launching weather balloon

BAS scientist launching a weather balloon in the Antarctic

A world without Montreal

The paper's authors write that such temperature changes at high latitudes "are larger than the global mean temperature changes projected over the next few decades, and perhaps comparable with projected regional changes." They add that this means the Protocol has "not only averted further damage to the ozone layer but has helped prevent significant regional climate change."

"The Montreal Protocol has already had a huge impact in terms of climate change, over and above the benefits that have come out of Kyoto," believes Pyle.

Scientists at the British Antarctic Survey's Halley Bay research base in the Antarctic were the first to notice the problem of ozone depletion. Geophysicist Joe Farman used an ageing instrument to spot a precipitous drop in levels of ozone above the south polar region. The discovery, which appeared in Nature in 1985, led to tougher limits on CFC emissions at Montreal.

At present the world is already due for temperature rises of around 0·2°C per decade. Increasing atmospheric chlorine to 9ppbv could add a few tenths of a degree to that rise. And ozone loss over both poles could cause Antarctic and Arctic average surface temperatures to rise by nearly 1°C.

By the end of the century, the impact on climate from CFC emissions could in some regions have been comparable in magnitude to the effects of greenhouse gas emissions predicted in the 2007 report of the United Nations Intergovernmental Panel on Climate Change.

Unsurprisingly, failing to take action at Montreal would have significantly harmed the ozone layer as well. Ozone levels would have fallen by around 5 per cent in the tropics, by between 10-15 per cent in middle latitudes, by around 30 per cent over the Arctic and by as much as 60 per cent over Antarctica.

These changes are much bigger than what has been observed, due in large part to the Montreal Protocol's restrictions. No significant changes in tropical ozone have been measured recently, and mid-latitude changes have hovered around 3 per cent in the northern hemisphere and around 6 per cent in the south. "The Montreal Protocol has prevented further, substantial ozone losses which would have led to increased surface UV radiation with consequences for human health," the report's authors state.

The predictions are based on computer models of the atmosphere, but scientists say it is borne out by the data. "The patterns of change the models predict are similar to the observed Antarctic patterns over the last 20 years, which gives us some confidence in the predictions," Pyle says.

The research was supported by NERC's National Centre for Atmospheric Science and by the European Commission through its SCOUT-O3 project.

'The World Avoided by the Montreal Protocol' - Morgenstern, OP Braesicke, MM Hurwitz, FM O'Connor, AC Bushell, CE Johnson, and JA Pyle (2008), Geophysical Research Letters, 35, L161811, doi:10.1029/2008GLO34590.