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Can pollution be good?

Stevens responds to a Nobel Laureate’s recent proposal

Could pollution in the atmosphere actually help to cool the planet? Prof. Phil Stevens responds to a plan presented at the United Nations' annual conference on climate change.

Expert perspective: “Paul Crutzen, who shared the Nobel Prize in Chemistry in 1995 for his contributions to our understanding of stratospheric ozone depletion, recently suggested that the injection of sulfate particles into the stratosphere using balloons should be considered to help slow the rate of global warming. Crutzen and other scientists are concerned about the slow response of the international community to the growing problem of global warming and feel that drastic measures must be considered. However, there are a number of scientists who are cautioning against performing a new experiment on the atmosphere by changing its composition, as we are already in the middle of an experiment with an uncertain outcome.

“The concept of using global environmental engineering to solve global environmental problems is not new. In the past, some have argued for fertilizing the ocean with iron to enhance the uptake of carbon dioxide by phytoplankton, while others have proposed injecting hydrocarbons into the stratosphere over Antarctica to scavenge chlorine atoms from chlorofluorocarbons and prevent them from destroying ozone. The idea of injecting sulfates into the atmosphere to reflect solar radiation and potentially provide a global cooling mechanism to offset global warming has also been proposed before. The difference is that this time a world-renowned atmospheric scientist and Nobel Laureate is the one proposing that we should consider this drastic step.

“Sulfate particles in the atmospheres come from a variety of natural and anthropogenic sources, including coal burning and volcanoes. There is evidence that these particles reflect solar radiation rather than absorb it, and as a result can reduce the amount of sunlight that reaches and warms the surface of the earth. As a result, high concentrations of sulfates may cool the planet. Although most volcanic eruptions do not produce enough sulfates to cause global effects, the eruption of Mount Pinatubo in 1991 injected approximately 10 million tons of sulfur dioxide into the stratosphere, which was converted to sulfate particles and spread globally. The following year the average temperature of the earth decreased by approximately 1 degree Fahrenheit, likely due to the cooling effect of these particles. The effect was only temporary, as these particles eventually rain out of the atmosphere. A similar cooling effect may also occur as a result sulfur dioxide emissions from coal combustion, but the lifetime of sulfates in the lower atmosphere is much shorter, as the sulfate particles rain out quickly and contribute to acid deposition.

“However, these particles have other global effects on the environment, such as enhancing the rate of stratospheric ozone depletion by chlorofluorocarbons. There is evidence that the concentration of ozone in the stratosphere decreased globally by approximately ten percent during the year after the eruption of Mount Pinatubo. This and potentially other unknown effects of sulfate particles on the global environment, in addition to the cost and technical difficulties associated with repeated injections into the stratosphere, are the main arguments against the injection of sulfates directly into the stratosphere.”


The SPEA Toolkit: Phil Stevens is an associate professor at SPEA who focuses on the characterization of the chemical mechanisms in the atmosphere that influence regional air quality and global climate change. He is a recent recipient of a Faculty Early Career Development (CAREER) award from the National Science Foundation, and is a member of the Indiana Air Pollution Control Board.


Click here to learn more about Phil Stevens.

Click here to read more about Paul Crutzen’s proposal.