An international team of scientists, including University of Maryland Professor Ross Salawitch, say that a widely-discussed idea to offset global warming by injecting sulfate particles into the stratosphere would significantly damage Earth’s protective ozone layer. 

Artificially Cooling the Planet Would Carry Big Price

Some climate scientists, who are concerned that the world is not acting quickly enough to counteract global warming, have proposed a plan to regularly inject sulfate particles into the stratosphere (the second major layer of Earth's atmosphere, just above the troposphere). The aerosols would reflect sunlight and cool the planet. Sulfur particles spewed from major volcanic eruptions, such as Mount Pinatubo in the Philipines in 1991, have reduced surface temperatures on Earth for the several year time period of enhanced aerosol loading. Yet the cooling effect of Mount Pinatubo came with a price – a 2-3% reduction in the thickness of the ozone layer at mid-latitudes and larger losses in the Arctic. The ozone layer protects Earth and its inhabitants from the ultraviolet light of the sun.

Restoring the Ozone Layer

Tilmes, Müller, and Salawitch studied the effects of the Mount Pinatubo eruption, analyzed the chemical actions of sulfur in the atmosphere, and modeled the potential impact of an attempted geoengineering effort.  They found that adding sulfur to the atmosphere would spark chemical reactions leading to the liberation of chlorine, a compound known to destroy ozone, with the largest effects felt during winters when the Arctic stratosphere was particularly cold. “Adding sulfur to the stratosphere would undo our efforts of the past two decades to restore the ozone layer,” says Dr. Salawitch, who was involved in studies that helped support the Montreal Protocol, the landmark international treaty passed in 1987 which restricted the industrial production of CFCs (chlorofluorocarbons) and other ozone depleting substances.   

Averting a Climate Catastrophe

In their analysis of current geoengineering proposals, the Tilmes group found that injections of small sulfate particles over the next 20 years could reduce the ozone layer in the Arctic by 100 to 230 Dobson Units. The average thickness of the ozone layer in the Northern Hemisphere is 300 to 450 Dobson Units. (A Dobson Unit is a common measure of the thickness of the ozone layer.)
“Climate change is a very serious issue and we need to continue to research mitigation strategies to avert a climate catastrophe from a broad perspective,” urges Salawitch. “Our paper does not preclude geoengineering approaches, but we believe this specific idea would have serious undesirable consequences.”

Dr. Salawitch, who is a professor with UM’s Departments of Chemistry and Biochemistry, as well as Atmospheric and Oceanic Science, and the Earth System Science Interdisciplinary Center, contributes expertise to a variety of atmospheric composition and climate change research projects led by NASA, and participated in the Intergovernmental Panel on Climate Change, which together with Al Gore won the 2007 Nobel Peace Prize for its efforts to build and disseminate greater knowledge about climate change.  Salawitch recently testified to the Maryland State Senate about the scientific basis of global warming in support of the Global Warming Solutions Act.

The paper The Sensitivity of Polar Ozone Depletion to Proposed Geoengineering Schemes can be found online at Science Express.