Columbia engineering study links ozone hole to climate change all the way to the equator
First time that ozone depletion is shown to impact the entire circulation of the southern hemisphere
In a study to be published in the April 21st issue of Science magazine, researchers at Columbia University’s School of Engineering and Applied Science report their findings that the ozone hole, which is located over the South Pole, has affected the entire circulation of the Southern Hemisphere all the way to the equator. While previous work has shown that the ozone hole is changing the atmospheric flow in the high latitudes, the Columbia Engineering paper, “Impact of Polar Ozone Depletion on Subtropical Precipitation,” demonstrates that the ozone hole is able to influence the tropical circulation and increase rainfall at low latitudes in the Southern Hemisphere. This is the first time that ozone depletion, an upper atmospheric phenomenon confined to the polar regions, has been linked to climate change from the Pole to the equator.
“The ozone hole is not even mentioned in the summary for policymakers issued with the last IPCC report,” noted Lorenzo M. Polvani, Professor of Applied Mathematics and of Earth & Environmental Sciences, Senior Research Scientist at the Lamont-Doherty Earth Observatory, and co-author of the paper. “We show in this study that it has large and far-reaching impacts. The ozone hole is a big player in the climate system!”
“It’s really amazing that the ozone hole, located so high up in the atmosphere over Antarctica, can have an impact all the way to the tropics and affect rainfall there — it’s just like a domino effect,” said Sarah Kang, Postdoctoral Research Scientist in Columbia Engineering’s Department of Applied Physics and Applied Mathematics and lead author of the paper.
The ozone hole is now widely believed to have been the dominant agent of atmospheric circulation changes in the Southern Hemisphere in the last half century. This means, according to Polvani and Kang, that international agreements about mitigating climate change cannot be confined to dealing with carbon alone— ozone needs to be considered, too. “This could be a real game-changer,” Polvani added.
Located in the Earth’s stratosphere, just above the troposphere (which begins on Earth’s surface), the ozone layer absorbs most of the Sun’s harmful ultraviolet rays. Over the last half-century, widespread use of manmade compounds, especially household and commercial aerosols containing chlorofluorocarbons (CFCs), has significantly and rapidly broken down the ozone layer, to a point where a hole in the Antarctic ozone layer was discovered in the mid 1980s. Thanks to the 1989 Montreal Protocol, now signed by 196 countries, global CFC production has been phased out. As a result, scientists have observed over the past decade that ozone depletion has largely halted and they now expect it to fully reverse, and the ozone hole to close by midcentury.
But, as Polvani has said, “While the ozone hole has been considered as a solved problem, we’re now finding it has caused a great deal of the climate change that’s been observed.” So, even though CFCs are no longer being added to the atmosphere, and the ozone layer will recover in the coming decades, the closing of the ozone hole will have a considerable impact on climate. This shows that through international treaties such as the Montreal Protocol, which has been called the single most successful international agreement to date, human beings are able to make changes to the climate system.
Together with colleagues at the Canadian Centre for Climate Modelling and Analysis in Victoria, BC, Kang and Polvani used two different state-of-the-art climate models to show the ozone hole effect. They first calculated the atmospheric changes in the models produced by creating an ozone hole. They then compared these changes with the ones that have been observed in the last few decades: the close agreement between the models and the observations shows that ozone has likely been responsible for the observed changes in Southern Hemisphere.
This important new finding was made possible by the international collaboration of the Columbia University scientists with Canadian colleagues. Model results pertaining to rainfall are notoriously difficult to calculate with climate models, and a single model is usually not sufficient to establish credible results. By joining hands and comparing results from two independent models, the scientists obtained solid results.
Kang and Polvani plan next to study extreme precipitation events, which are associated with major floods, mudslides, etc. “We really want to know,” said Kang, “if and how the closing of the ozone hole will affect these.”
This study was funded by a grant from the National Science Foundation to Columbia University.
Columbia University’s Fu Foundation School of Engineering and Applied Science, founded in 1864, offers programs in nine departments to both undergraduate and graduate students. With facilities specifically designed and equipped to meet the laboratory and research needs of faculty and students, Columbia Engineering is home to NSF-NIH funded centers in genomic science, molecular nanostructures, materials science, and energy, as well as one of the world’s leading programs in financial engineering. These interdisciplinary centers are leading the way in their respective fields while individual groups of engineers and scientists collaborate to solve some of society’s more vexing challenges. http://www.engineering.columbia.edu/
Impact of Polar Ozone Depletion on Subtropical Precipitation
Kang et al 2011, Science Express
Over the past half-century, the ozone hole has caused a
poleward shift of the extratropical westerly jet in the
Southern Hemisphere. Here, we argue that these
extratropical circulation changes, resulting from ozone
depletion, have substantially contributed to subtropical
precipitation changes. Specifically, we show that
precipitation in the Southern subtropics in austral
summer increases significantly when climate models are
integrated with reduced polar ozone concentrations.
Furthermore, the observed patterns of subtropical
precipitation change, from 1979 to 2000, are very similar
to those in our model integrations, where ozone depletion
alone is prescribed. In both climate models and
observations, the subtropical moistening is linked to a
poleward shift of the extratropical westerly jet. Our
results highlight the importance of polar regions on the
subtropical hydrological cycle.
Fig. 4. Mechanism linking the ozone hole to subtropical
precipitation change. Shading is the zonal-mean response in
austral summer of (A and D), temperature (in K), (B and E),
zonal wind (in m s–1), and (C and F), mean meridional mass
streamfunction (in 109 kg s–1). Black solid contours in (A) and
(D) are the mean temperatures, and red dashed lines indicate
the tropopause height in the reference integrations; the arrows
illustrate the lifting of tropopause in response to ozone
depletion. Black solid (dashed) contours in (B) and (E) are
the mean westerlies (easterlies) in the reference integrations,
and the arrows illustrate the direction of extratropical
westerly jet shift. Black solid (dashed) contours in (C) and (F)
are the clockwise (counter-clockwise) mean meridional
circulation in the reference integrations, and the arrows
illustrate the direction of anomalous vertical motion induced
by ozone depletion. Top row: the coupled CMAM
integrations [experiment (i)]. Bottom row: the uncoupled
CAM3 integrations with ozone depletion confined to 40-90°S
Full paper here: Kang-04-22-11 (PDF)
Supplemental material: kangSOM110422 (PDF)
UPDATE: BTW, in case anybody cares, this post went up 30 minutes AFTER the media embargo was lifted at 14:00 EST April 21. Compare that to the big argument going on over the Nisbet report. I have to agree with Keith Kloor on this one. Breaking embargoes is not only unprofessional, it is a fast track to excluding oneself from receiving any further media pre-releases. – Anthony