Aerosol particles and cloud droplets -- Microscopic modulators of climate

Scientists use the Community Climate System Model to increase their understanding of the world's climate patterns and learn how they may affect regions around the globe.

Scientists around the world use sophisticated computer models to simulate future scenarios of all types— including global climate. Researchers at Pacific Northwest National Laboratory are playing a key role in the improvement of these models by providing new information about the role of aerosols in the atmosphere.

Aerosols are tiny particles that are continually present in Earth’s atmosphere as the result of either natural or manmade processes. Whether in solid (smoke, dust) or liquid (sea salt, sulfuric acid) form, aerosols affect Earth’s climate in two ways: directly, through scattering and absorption of solar and infrared radiation, and indirectly, by influencing the creation of cloud droplets. More cloud droplets leads to increased surface area, in turn increasing the amount of energy reflected from the clouds and back into space. The degree to which these different aerosol effects impact the Earth’s energy balance is a critical element in climate simulations.

In spring 2006, a technique for aerosol treatment developed by PNNL researchers was implemented in the Community Climate System Model (CCSM), one of the world’s leading global climate models. Prior to that time, the model did not take into account the indirect effect of aerosols, which is considered a major contributor to the energy feedbacks that modulate Earth’s climate.

Steve Ghan, a PNNL staff scientist who developed the new aerosol treatment, worked with researchers at the National Center for Atmospheric Research, where the CCSM is maintained, to analyze the results from the new simulations.

“As expected, there are significant differences from the previous version of the model,” said Ghan. “The new version is sensitive to treatment of aerosols, and that’s what we’re concentrating on now.”

Ghan and his PNNL colleagues are implementing a new scheme for aerosol treatment in the CCSM that includes aerosol particles within cloud droplets. They expect this to improve the simulation of cloud-aerosol interactions by allowing for a more realistic treatment of cloud effects on aerosols, as well as aerosol effects on clouds.