The climate is a complex system controlled by the balance of energy between the Earth and space. The Earth receives a continuous influx of radiation from the sun. Some of this radiation is absorbed directly by the Earth's surface and the atmosphere. Some of this radiation is reflected back into space. Roughly two-thirds of this reflectivity is due to clouds and small particles in the atmosphere called aerosols.
Aerosols interact with the Earth's energy balance in two very different ways—directly and indirectly. As a direct effect, aerosols both absorb and scatter sunlight. This reduces the amount of solar energy that reaches the Earth's surface, resulting in a cooling effect on the planet. As an indirect effect, aerosols can interact with and modify cloud properties. These interactions also impact the Earth's energy budget, although there are significant gaps in our understanding of what these impacts are.
Much of the uncertainty in projections of global climate change is due to the complexity of clouds, aerosols, and cloud-aerosol interactions, and the difficulty of incorporating this information into climate models. In view of the significance of climate forcing by both man-made and natural aerosols and the relatively undeveloped ability to incorporate this forcing into climate models, Pacific Northwest National Laboratory (PNNL) has undertaken the Aerosol Climate Initiative to address critical scientific questions related to aerosols and their impact on climate. Our vision, mission and approach for this research takes into account the complexity of climate science and the need for key advances that will help decision makers as they face policy challenges related to the environment.
The Aerosol Chemistry and Climate Institute combines the considerable resources of PNNL and the University of California San Diego, advancing the scientific understanding of how aerosols affect global climate change.