Nav: Home

The ozone layer continues to thin

February 06, 2018

The ozone layer protects life on earth from high-energy radiation. In the 20th century, when excessive quantities of ozone-depleting chlorinated and brominated hydrocarbons (e.g. CFCs) were released into the atmosphere, the ozone layer in the stratosphere - i.e. at altitudes of 15 to 50 km - thinned out globally. The Montreal Protocol introduced a ban on these long-lasting substances in 1989.

At the turn of the millennium, the loss of stratospheric ozone seemed to have stopped. Until now, experts have expected that the global ozone layer would completely recover by the middle of the century.

Further dilution in the lower stratosphere

An international team led by researchers from ETH Zurich and the Physikalisch-Meteorologisches Observatorium Davos have now made a troubling discovery: despite the ban on CFCs, the concentra-tion of ozone in the lower part of the stratosphere (15 to 24 km) - where the ozone layer is at its den-sest - has contined to decline at latitudes between 60° S and 60° N. The scientists were able to de-monstrate this using satellite measurements spanning the last three decades together with advanced statistical methods. They report on their work in the latest issue of the journal Atmospheric Chemistry and Physics.

Contrasting processes mask trend

Ozone is formed in the stratosphere, mainly at altitudes above 30 km in the tropics. From there it is distributed around the globe by atmospheric circulation. The scientists were somewhat surprised that the ozone is thinning out in the lower stratosphere because their models do not show this trend and CFCs continue to decline. Certain aspects of their findings are not completely unexpected, however. William Ball, an atmospheric researcher at ETH Zurich and the first author of the study, explains: "Thanks to the Montreal Protocol, ozone in the upper stratosphere - i.e. above 30 km - has increased significantly since 1998, and the stratosphere is also recovering above the polar regions." Yet despite these increases, measurements show that the total ozone column in the atmosphere has remained constant, which experts took as a sign that ozone levels in the lower stratosphere must have declined.

The negative trend had nevertheless not yet been demonstrated. This is partly due to the fact that ozone is also formed in the troposphere - at altitudes below about 15 km - by human activities. "This anthropogenic ozone, which causes summer smog, partially masks the stratospheric decline in the satellite measurements," said Ball.

Circulation and short-lived chemicals

The reasons for the continuing decline are still unclear. However, the authors have two possible ex-planations. On the one hand, climate change is modifying the pattern of atmospheric circulation, mov-ing air from the tropics faster and further in the polar direction, so that less ozone is formed.

On the other hand, very short-lived substances (VSLSs) containing chlorine and bromine are on the rise, and could increasingly enter the lower stratosphere, for example as a result of more intense thunderstorms. Ozone-depleting VSLSs are partly of natural and partly of industrial origin; some are substitutes for CFCs, and although they are less ozone-depleting, they are not neutral either. "These short-lived substances could be an insufficiently considered factor in the models," says Ball.

Clarifying causes and impact

It is not yet possible to assess the consequences that this continuing lower stratospheric ozone de-pletion will have for humans and the ecosystem. For Thomas Peter, ETH Professor of Atmospheric Chemistry and co-author of the study, the findings are concerning but not alarming. "The decline now observed is far less pronounced than before the Montreal Protocol. The impact of the Protocol is undisputed, as evidenced by the trend reversal in the upper stratosphere and at the poles. But we have to keep an eye on the ozone layer and its function as a UV filter in the heavily populated mid-latitudes and tropics," he says.

With the help of global climate models, the scientists now want to investigate the causes behind the continuing lower stratospheric ozone decline.
-end-


ETH Zurich

Related Climate Change Articles:

The black forest and climate change
Silver and Douglas firs could replace Norway spruce in the long run due to their greater resistance to droughts.
For some US counties, climate change will be particularly costly
A highly granular assessment of the impacts of climate change on the US economy suggests that each 1°Celsius increase in temperature will cost 1.2 percent of the country's gross domestic product, on average.
Climate change label leads to climate science acceptance
A new Cornell University study finds that labels matter when it comes to acceptance of climate science.
Was that climate change?
A new four-step 'framework' aims to test the contribution of climate change to record-setting extreme weather events.
It's more than just climate change
Accurately modeling climate change and interactive human factors -- including inequality, consumption, and population -- is essential for the effective science-based policies and measures needed to benefit and sustain current and future generations.
Climate change scientists should think more about sex
Climate change can have a different impact on male and female fish, shellfish and other marine animals, with widespread implications for the future of marine life and the production of seafood.
Climate change prompts Alaska fish to change breeding behavior
A new University of Washington study finds that one of Alaska's most abundant freshwater fish species is altering its breeding patterns in response to climate change, which could impact the ecology of northern lakes that already acutely feel the effects of a changing climate.
Uncertainties related to climate engineering limit its use in curbing climate change
Climate engineering refers to the systematic, large-scale modification of the environment using various climate intervention techniques.
Public holds polarized views about climate change and trust in climate scientists
There are gaping divisions in Americans' views across every dimension of the climate debate, including causes and cures for climate change and trust in climate scientists and their research, according to a new Pew Research Center survey.
The psychology behind climate change denial
In a new thesis in psychology, Kirsti Jylhä at Uppsala University has studied the psychology behind climate change denial.

Related Climate Change Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Climate Crisis
There's no greater threat to humanity than climate change. What can we do to stop the worst consequences? This hour, TED speakers explore how we can save our planet and whether we can do it in time. Guests include climate activist Greta Thunberg, chemical engineer Jennifer Wilcox, research scientist Sean Davis, food innovator Bruce Friedrich, and psychologist Per Espen Stoknes.
Now Playing: Science for the People

#527 Honey I CRISPR'd the Kids
This week we're coming to you from Awesome Con in Washington, D.C. There, host Bethany Brookshire led a panel of three amazing guests to talk about the promise and perils of CRISPR, and what happens now that CRISPR babies have (maybe?) been born. Featuring science writer Tina Saey, molecular biologist Anne Simon, and bioethicist Alan Regenberg. A Nobel Prize winner argues banning CRISPR babies won’t work Geneticists push for a 5-year global ban on gene-edited babies A CRISPR spin-off causes unintended typos in DNA News of the first gene-edited babies ignited a firestorm The researcher who created CRISPR twins defends...