ScienceDaily (Jan. 19, 2004) — Atmospheric researchers have provided observational evidence that burning fossil fuels has a direct impact on the solar radiation reflectivity of clouds, thereby contributing to global climate change.

Joyce Penner, professor in the University of Michigan Department of Atmospheric, Oceanic and Space Sciences, U-M graduate student Yang Chen, and assistant professor Xiquan Dong from the University of North Dakota Department of Atmospheric Science, reported their findings in the Jan. 15 issue of the journal Nature.

Most evidence that increased levels of fossil fuel particles (aerosols) affects the reflectivity of clouds, thereby producing a cooling effect on the climate, has been indirect. "This made it difficult to determine the impact this phenomena, known as the indirect aerosol effect, has on the global climate," Penner said. "Our data makes the direct connection and opens new areas of study."

Solar radiation, which adds to global warming, is reflected back into space by clouds. Cloud droplets are increased with higher levels of aerosols, allowing for less radiation, or heat, to reach the lower atmosphere. The end result is a measurable cooling effect on the climate.

Using atmospheric data gathered from a site in Oklahoma, a typical continental site with a high concentration of aerosols, and a typical Arctic site in Barrow Alaska with low aerosol concentration, the researchers were able to show that the difference in cloud reflectivity at the two sites was caused by the difference in aerosol levels. The researchers also provided important evidence that the computer simulation model used in the study was capable of estimating cloud optical properties determined over a broad range of aerosol concentrations.

"This study is important for two reasons," Penner said. "First, it provides evidence that there is some cooling of the climate due to anthropogenic aerosols. Second, the simulation model we used has been shown to be a valuable tool in determining more directly the impact of aerosols on the climate."

Penner cautioned that over longer time scales in the future, the climate cooling due to the indirect aerosol effect will be minimal when compared to the climate warming of carbon dioxide. "We've shown that there's more work to be done to discover all of the various ways we affect the climate."

For more information, visit http://aoss.engin.umich.edu/ and http://www.nature.com/

Related Stories

Forest Burning Is A Net Contributor To Global Warming, Scientist Says (Aug. 24, 2004) — What is the net effect on global temperature of the gases and particles produced when biomass is burned? That long-standing question in climate change has finally been answered, according to Mark Z. ...  > read more

Go Solar, Wind Or Geothermal If You Want Renewable Energy With Life-cycle Efficiency (Aug. 18, 2007) — Do the overall efficiencies of renewable energy sources add up in terms of their complete life cycle from materials sourcing, manufacture, running, and decommissioning? Using these criteria, ...  > read more

Next Ice Age Delayed By Rising Carbon Dioxide Levels (Aug. 30, 2007) — Future ice ages may be delayed by up to half a million years by our burning of fossil fuels. Arguably, this work demonstrates the most far-reaching disruption of long-term planetary processes yet ...  > read more

New View On The Culprits Of Climate Change (Aug. 30, 2000) — For many years, researchers agreed that climate change was triggered by what they called "greenhouse gases," with carbon dioxide (CO2) from burning of fossil fuels such as coal, oil, and gas, ...  > read more

Global Warming Will Persist At Least A Century Even If Emissions Curbed Now (Feb. 18, 2002) — Though significant uncertainty remains regarding the amount of global warming that will occur over the next century or two, scientists agree that the trend will continue for the next hundred years ...  > read more

Search ScienceDaily

Bringing Sunlight Inside