Ozone layer recovery could be delayed by a rise in a gas commonly used in paint strippers
28 June 2017
If recent and rapid increases in a gas commonly used as a paint stripper and in the food industry to decaffeinate coffee and tea continue, the recovery of the ozone hole could be delayed by up to 30 years, say researchers.
Antarctic ozone hole: 1979 to 2008
Their findings, published this week in the scientific journal Nature Communications, suggest that a previously ignored chemical called dichloromethane, not controlled by the Montreal Protocol, may now be contributing to ozone depletion and should be considered to improve future predictions of ozone recovery.
The Montreal Protocol is heralded by many as one of the most successful international agreements ever. Introduced in 1987, the agreement followed many decades of monitoring of the ozone hole over Antarctica by researchers at NERC's British Antarctic Survey.
The agreement led to the regulation of emissions of ozone-depleting gases, after which stratospheric ozone began to recover. The ozone hole, which is largest around October every year, is projected to return to pre-1980 levels in the second-half of this century, and fully recover sometime between 2046 and 2057.
Lead author of the study, Dr Ryan Hossaini of Lancaster University, who is funded by NERC, said:
"Dichloromethane is a man-made ozone-depleting chemical that has a range of industrial applications. Unlike chlorofluorocarbons (CFCs) and similar long-lived gases that are responsible for most ozone depletion, dichloromethane has a short atmospheric lifetime so has not been controlled by the Montreal Protocol. Despite this, increased production has led to a rapid increase in its atmospheric concentration over the past decade.
While ozone depletion from dichloromethane is currently quite modest, it is uncertain how the amount of this gas in the atmosphere will change in the future. Our results show that continued sustained growth in its concentration could substantially delay recovery of the ozone layer, offsetting some of the future benefits of the Montreal Protocol."
Dr Hossaini and colleagues used sophisticated computer models of the atmosphere to show that the gas's effect on ozone has increased significantly in recent years. They also analysed measurements of dichloromethane in the atmosphere over the past two decades, provided by scientists from the National Oceanic & Atmospheric Administration (NOAA) in the United States.
Study co-author Dr Stephen Montzka from NOAA said:
"The increases observed for dichloromethane from our measurements are striking and unexpected; concentrations had been decreasing slowly in the late 1990s, but since the early 2000s have increased by about a factor of two at sites throughout the globe. It is uncertain what is driving this growth. However, it could be related to increased use of this chemical as a solvent in place of other long-lived chemicals (for example CFCs and hydrochlorofluorocarbons) that have been phased out, or from use as feedstock in the production of other chemicals."
The researchers projections show that continued dichloromethane increases at the average trend seen from 2004 to 2014 would delay ozone recovery over Antarctica by 30 years. If dichloromethane concentrations stay at current levels, the delay in recovery would be only five years. Although the future trajectory of dichloromethane is uncertain, without any regulations on emissions, it is likely concentrations will fall somewhere in between these ranges.
The ozone layer shields Earth's surface from certain wavelengths of harmful solar ultraviolet radiation that would otherwise be detrimental to human, animal and plant health. Ozone also absorbs terrestrial infrared radiation and changes in its abundance can influence climate.
A NERC-commissioned analysis in 2015 found that NERC's ozone research has spared thousands of lives and led to lower food prices, leading to savings of £1·3 billion every year for the UK, thanks to the early implementation of the Montreal Protocol.
The analysis estimated that, had NERC-funded scientists at NERC's British Antarctic Survey not reported their discovery of a hole in the ozone layer in 1985, its discovery might have been delayed by five to ten years. By 2030, the cost of this delay would have resulted in 300 more skin cancer cases every year in the UK, costing the country around £550 million a year in today's money. The analysis, by Deloitte, estimates the discovery also led to avoided losses in farm production worth up to £740 million a year.
NERC's Associate Director of Research, Dr Ned Garnett, said:
"It's encouraging to see that our continued investment in ozone research is leading to important findings such as this one, and evidence for policymakers. NERC's British Antarctic Survey has invested over £14 million in ozone monitoring since 1957, and NERC has funded on average £1·5 million on ozone research every year since 2004."
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