Study of Aerosols May Improve Climate Models

Researchers at NASA's Jet Propulsion Laboratory (JPL) studying aerosols, tiny particles in Earth's atmosphere, are finding that their research could yield better climate models. This will possibly allow scientists to better understand Earth's changing climate amidst global warming.

Aerosols are partly responsible for helping cool our planet. They scatter and absorb incoming sunlight and affect the formation and properties of clouds. Among all cloud types, low-level clouds over the ocean - which cover about one-third of the ocean's surface - have the biggest impact on the albedo, or reflectivity, of Earth's surface. By reflecting solar energy back to space, aerosols effectively cool down Earth's atmosphere.

Now, using a new, comprehensive global analysis of satellite data, JPL researchers and a team from the California Institute of Technology in Pasadena have quantified how changes in aerosol levels affect these warm clouds over the ocean.

The findings were published Aug. 3 in the journal Nature Geoscience.

Changes in aerosol levels have two main effects: they alter the amount of clouds in the atmosphere and change their properties.

Water vapor condenses on aerosol particles into cloud droplets or cloud ice particles, so more aerosols in the air means more clouds. And within these clouds, increased aerosol levels can either raise or lower the amount of liquid water they contain. Though, this depends on whether the clouds are raining or not, the stability of the atmosphere and humidity levels in the upper troposphere.

The research team analyzed 7.3 million individual data points from multiple satellites in the international constellation of Earth observing satellites - known as the Afternoon Constellation, or A-Train - from August 2006 to April 2011. This provided the first detailed estimate of both of aerosols' effects on clouds.

What they found was that each effect was of similar magnitude - meaning, changing the amount of the clouds and changing their internal properties are both equally important in their contribution to cooling our planet. Furthermore, the total impact from the influence of aerosols on this type of cloud is almost double that estimated in the latest report of the United Nations' Intergovernmental Panel on Climate Change.

"These results offer unique guidance on how warm cloud processes should be incorporated in climate models with changing aerosol levels," John Seinfeld, the Louis E. Nohl professor and professor of chemical engineering at Caltech, said in a statement.

The research was funded by NASA and the Office of Naval Research.