Evidence shows increased risk of ozone loss over the US in summer

June 5, 2017
Credit: Harvard University

A new study out of Harvard University reveals that the protective stratospheric ozone layer above the central United States is vulnerable to erosion during the summer months from ozone-depleting chemical reactions, exposing people, livestock and crops to the harmful effects of UV radiation.

Powerful storm systems common to the Great Plains inject water vapor that, with observed temperature variations, can trigger the same over the central United States that are the cause of loss over the polar regions, according to a new paper published in the Proceedings of the National Academy of Sciences.

The paper, led by James G. Anderson, the Philip S. Weld Professor of Atmospheric Chemistry at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), found that concentrations over the United States in summer are vulnerable to both increases in water vapor and observed variations in temperature from storm systems over the Great Plains. Increased frequency and intensity of these storm systems, as well as longer-term decreases in stratospheric temperatures, are expected to accompany climate change.

Using extensive aircraft observations in the Arctic stratosphere from the early 2000's, researchers established the chemical framework defining enhanced ozone loss rates with respect to temperature and water vapor. Then they employed recent NEXRAD weather radar observations to demonstrate that on average 4000 storms each summer penetrate into the stratosphere over the central United States, which is far more frequent than was previously thought.

This combination of circumstances puts the stratosphere over states including Texas, Oklahoma, Kansas, Nebraska, Iowa, Missouri, the Dakotas and that border the Great Plains, at risk for chemical reactions that deplete ozone during summer, potentially leading to higher levels of exposure to damaging UV light from the sun.

"These developments were not predicted previously and they represent an important change in the assessment of the risk of increasing UV radiation over the central US in summer," said Mario J. Molina of the University of California San Diego, the 1995 Nobel Prize winner in stratospheric chemistry, who was not involved in this research.

Stratospheric ozone is one of the most delicate aspects of habitability on the planet. There is only marginally enough ozone in the stratosphere to provide protection from UV radiation for humans, animals and crops. Medical research specific to the United States has determined that a 1 percent decrease in the amount of ozone in the stratosphere corresponds to a 3 percent increase in the incidence of human skin cancer. There are now 3.5 million new cases of skin cancer each year reported in the US alone. Thus, for each 1 percent reduction in ozone, there would be an additional 100,000 new cases of skin cancer annually in the United States.

"Thunderstorms that hydrate the stratosphere can have significant local and regional impacts on Earth's radiation budget and climate," said Cameron R. Homeyer of the University of Oklahoma, a co-investigator on the paper. "This work demonstrates our increasing knowledge of such storms using ground-based and airborne observations and evaluates their potential for depleting stratospheric ozone now and in the future. The results strongly motivate the need for increased meteorological and chemical observations of such storms."

"Every year, sharp losses of stratospheric ozone are recorded in polar regions, traceable to chlorine and bromine added to the atmosphere by industrial chlorofluorocarbons and halons," said Steven C. Wofsy, the Abbott Lawrence Rotch Professor of Atmospheric and Environmental Science at SEAS and co-author of the study. "The new paper shows that the same kind of chemistry could occur over the central United States, triggered by storm systems that introduce water, or the next volcanic eruption, or by increasing levels of atmospheric carbon dioxide. We don't yet know just how close we are to reaching that threshold."

The scientific community has observed the chemical reactions that attack ozone over the polar regions in winter, but the important combination of observations that define the cause and the rate of stratospheric ozone loss have never been made over the central US in summer. This represents a major shortcoming in researchers' ability to forecast increases in UV radiation that might result from a volcanic event or climate change now and in the years to come.

"Rather than large continental-scale ozone loss that occurs over the in winter characterized, for example, by the term Antarctic ozone hole, circumstances over the central US in summer are very different," said Anderson. "In particular, because of the very frequent storm-induced injection events detailed by studies at Texas A&M and the University of Oklahoma using advanced radar methods, this structure of highly localized but numerous regions of potential ozone loss requires carefully specified observational strategies and systematic surveillance in order to provide the basis for accurate weekly forecasts of ozone loss."

The researchers are calling for extensive characterization of the stratosphere over the central United States in order to forecast short-term and long-term related to increasing frequency and intensity of storm systems, higher levels of atmospheric carbon dioxide and methane, and other factors.

Explore further: 2016 Antarctic ozone hole attains moderate size, consistent with scientific expectations

More information: James G. Anderson el al., "Stratospheric ozone over the United States in summer linked to observations of convection and temperature via chlorine and bromine catalysis," PNAS (2017). www.pnas.org/cgi/doi/10.1073/pnas.1619318114

Related Stories

Explaining Antarctic ozone hole anomalies

July 15, 2011

The strongly reduced Antarctic stratospheric ozone hole destruction in 2010 and several other recent years results from the occurrence of dramatic meteorological events in the polar winter, known as sudden stratospheric warmings ...

Strong ozone depletion above the arctic possible

February 18, 2016

This winter, the Arctic stratosphere so far has been unusually cold. Hence, all prerequisites are given for strong ozone depletion in the next weeks. This conclusion is based on first results of the POLSTRACC measurement ...

Team measures lightning-produced ozone with Lidar

February 17, 2016

Scientists at The University of Alabama in Huntsville (UAH) have used UAH's Rocket-city Ozone (O3) Quality Evaluation in the Troposphere (RO3 QET) Lidar to measure ozone that was chemically produced by summertime lightning ...

Recommended for you

4 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

aksdad
1 / 5 (4) Jun 05, 2017
Increased frequency and intensity of these storm systems, as well as longer-term decreases in stratospheric temperatures, are expected to accompany climate change.

How do they know that? Answer: they don't. They infer it from the computer-generated global circulation (climate) models. Which are wrong. Which you can see here, comparing models to real-world observations of temperature:

https://www.ipcc....S-14.jpg

The latest IPCC report (AR5, 2013) found that ALL of the climate models overstated warming. If your models don't accurately reproduce the natural world, then any predictions based on them are...wait for it...utterly useless.
jongogurmola
5 / 5 (5) Jun 05, 2017
aksdad, they use over a decade of NEXRAD radar data (actual data, not climate models) to observe the frequency of 'overshooting tops' and find that the frequency of overshooting tops is increasing quite substantially. The model they use isn't a GCM at all, but a CTM which doesn't include interactive climatology.

A swing and a miss. Strike three! you're wrong on all counts.
omegatalon
not rated yet Jun 05, 2017
Perfect timing of this article just after Donald Trump said he would withdraw the United States from the Paris Climate Accord.
howhot3
5 / 5 (1) Jun 06, 2017
they infer it from the computer-generated global circulation (climate) models. Which are wrong

How do you know they are wrong? What makes you the authority on climate models of any type?

Your absolute arrogance @askdad befuddles the human mind.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.