July 13, 2006: NASA scientists have determined the formation of clouds is affected by the lightness or darkness of air pollution particles. This also impacts Earth’s climate. In a breakthrough study published on July 13 in the online edition of Science, scientists explain why aerosols — tiny particles suspended in air pollution and smoke — sometimes stop clouds from forming and in other cases increase cloud cover. Clouds deliver water around the globe, and they also help regulate how much of the sun’s warmth the planet holds. The capacity of air pollution to absorb energy from the sun is the key.
With this new understanding, scientists working to predict how the Earth’s climate is changing will be able to take a big step forward. The effect of the planet’s constantly changing cloud cover has long been a problem for climate scientists. How clouds change in response to greenhouse-gas warming and air pollution will have a major impact on future climate.
“When the overall mixture of aerosol particles in pollution absorbs more sunlight, it is more effective at preventing clouds from forming. When pollutant aerosols are lighter in color and absorb less energy, they have the opposite effect and actually help clouds to form,” said Lorraine Remer of NASA’s Goddard Space Flight Center, Greenbelt, Md. Remer worked closely with the study’s lead author, the late Yoram Kaufman of Goddard, on previous research into this perplexing “aerosol effect.”
Using this new understanding of how aerosol pollution influences cloud cover, Kaufman and co-author Ilan Koren of the Weizmann Institute in Rehovot, Israel, estimate the impact world-wide could be as much as a 5 percent net increase in cloud cover. In polluted areas, these cloud changes can change the availability of fresh water and regional temperatures.