The Advantages of Acid Rain

Acid rain comes in the form of rain, fog, smog and dry depositions, and it harms forests, kills fish and erodes rocks and buildings. It is caused by excessive emissions of sulfur dioxide and nitrogen oxide compounds from industrial and natural sources. About two-thirds of sulfur dioxide and one-quarter of nitrogen oxides come from fossil-fuel-burning power plants. Some environmental studies indicate that the effects of acid rain are complex and include positive effects on global warming and improvement of forests.

Global Warming

Methane and carbon dioxide are major greenhouse gases that cause global warming. Methane, compared to carbon dioxide, is more potent. When compared by weight, methane has 20 times more of an impact on climate change than carbon dioxide does over a 100-year period, according to the U.S. Environmental Protection Agency. Methane is emitted from agricultural and industrial processes, but the largest source of methane entering the atmosphere is wetlands.

Suppressing Methane Production

About 22 percent of the human-enhanced greenhouse gas effect is due to methane. Microbes feeding on hydrogen- and acetate-containing vegetation in wetlands are natural contributors to total atmospheric methane. In a study of wetlands in Europe and North America, researchers at the Open University, U.K., found that sulfur compounds deposited by acid rain inhibited methane production by wetlands. The researchers found that methane production was significantly suppressed because sulfur-eating bacteria in wetland areas out-competed methane-emitting microbes. Sulfur compound deposition from acid rain can reduce methane production by up to 30 percent. In another study, the effects of acid rain on rice paddies were mimicked by adding small amounts of sulfate to the soil. Up to 24 percent of the methane was prevented from entering the atmosphere.

Forests

A 20-year-long study by scientists at Michigan Technological University School on the hardwood forests of Michigan found that acid rain, together with modest increases in temperature, makes forests more productive. Researchers measured nitrogen deposition by acid rain and found that trees store more carbon when the soil contains more nitrogen compounds, as long as there is enough moisture. Therefore, the increased growth rate and greater ability of trees to store carbon dioxide may offset some of the negative effects of acid rain on forests, such as damage to tree foliage.

Complex Effects of Acid Rain

Acid rain clearly has negative effects on the environment, but the beneficial effects of acid rain must enter into future predictions of its role in environmental damage and global warming. A computer model, created at NASA's Goddard Space Flight Center, predicts that the sulfur dioxide in acid rain will continue to suppress methane production by wetlands well into 2030. Although nitrogen oxide deposition by acid rain may have positive effects on forest trees, highly polluted acid rain damages trees and harms some animal species.