Over the past 40 years since the passage of the Clean Air Act, air pollution from automobiles, factories, and power plants has substantially decreased, leading to better human and environmental health. But air pollution and its impacts on people and ecosystems remain a concern amid growing demands for transportation, energy, and manufactured goods.
University and U.S. Forest Service researchers believe air pollution could also be a hidden driver of important changes in the nation’s watersheds following a recent study published in the January issue of the journal Climatic Change.
“We know that climate has major influences on water and carbon cycles, and that air pollution affects regional climate,” says Kai Duan, a North Carolina State University postdoctoral researcher working with the Eastern Forest Environmental Threat Assessment Center and the study’s lead author. He and a team of researchers combined a series of models, including a global climate model, a regional climate model, and the Water Supply Stress Index (WaSSI) model, to examine ecohydrological (carbon and water) responses to multiple future climate scenarios.
The scientists ran the models with and without accounting for the impacts of air pollution on climate in order to assess the individual and combined impacts of climate change and air pollution on water availability and ecosystem productivity. “Results from our study suggest that air pollution could aggravate climate change impacts on water shortages across U.S. regions,” says Duan.
Air pollution’s effects on climate and ecosystem dynamics are complex. Tiny particles present in air pollution such as smoke, dust, and some byproducts of burning fossil fuels—known as aerosols—can block sunlight from reaching the earth’s surface. Aerosols can affect the formation and behavior of clouds, provide a cooling effect on climate, and reduce trees’ photosynthesis, water use, and overall growth and productivity.
The effects of aerosols contrast the greenhouse effects of pollutants like carbon dioxide emitted during the burning of fossil fuels, which can increase trees’ productivity and water use. Further, nitrogen-based pollutants form acidic precipitation that fertilizes trees, which also increases productivity and water use.
Study results indicate that, while aerosols in air pollution could partially offset higher temperatures, greenhouse gases will continue to drive higher temperatures and associated increases in ecosystem water use.
Where future climate scenarios project warmer and wetter conditions, air pollution could reduce overall precipitation, and therefore water availability and ecosystem productivity. Researchers note that the impact of air pollution could be more complex and diverse at smaller local scales due to its interactions with other environmental factors.
With recent science and the national conversation focused on the climate impacts of greenhouse gases, the impacts of air pollution on water supplies and ecosystem productivity should not be overlooked.
“This study raises questions about the potential overestimation of precipitation based on projections from existing climate models that do not account for air pollution impacts,” says Eastern Threat Center research hydrologist Ge Sun. “Further studies that examine the effects of air pollution in a changing climate as well as the interactions of multiple environmental stressors are needed. Technologies that curb air pollution may have greater environmental benefits than expected.”
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For more information, email Ge Sun at gesun@fs.fed.us.