Aerosols are tiny particles, such as soot or dust, suspended in Earth's atmosphere. In addition to their impacts on air-quality, aerosols can block sunlight from reaching the Earth's surface. This image shows how much sunlight aerosols blocked from reaching the Earth's surface in 2006. Areas where aerosols let sunlight through are white, and areas where aerosols blocked sunlight from reaching the Earth are dark orange. Areas where data could not be collected appear in gray.
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Image Courtesy of Reto Stockli, NASA's Earth Observatory
Pollution Speeds up Snow Melt in Europe and Asia
Climate scientist Mark Flanner, an assistant professor at the University of Michigan led a study that looked into rates of springtime snow melt in Europe, Asia, and North America. The study found that the snow melts in the spring more quickly in Europe and Asia than in North America.
Flanner and his colleagues think that aerosols, especially black carbon and mineral dust might be responsible for this difference. The countries in Europe and Asia produce high levels of black carbon and mineral dust, which are types of air pollution. These particles blow across these two continents and affect the land surface and atmosphere.
Some aerosols reflect energy from the sun, which possibly cools the Earth's surface below. But black carbon and mineral dust tend to warm snow-covered surfaces by absorbing energy from the sun. Particulates that fall to the surface also reduce snow's albedo, which is it's ability to reflect sunlight back into the atmosphere. This means even more energy from the sun is absorbed by the land.
This study has affected how scientists can interpret climate models about North America, Europe, and Asia. Over North America, carbon dioxide (CO2) had more of an impact on springtime snow cover than black carbon and organic matter, but in Europe and Asia, as hypothesized, the particulates had almost as much of an effect as CO2.
"While this research does not fully explain why springtime land temperatures and snow cover are changing so much faster over Eurasia than North America, it does suggest that snow darkening from black carbon, a process lacking in most climate models, is playing a role," Flanner said.
Because snow covers much of the Northern Hemisphere during spring, Flanner and his colleagues expect to see some of the strongest climate change signals in these areas during the spring.
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