Atmospher Sci & Global Chg
Research Highlights

October 2012

Dimming the Sun's Light

Planet's sensitivity to greenhouse gases will determine how much shading could be needed to slow temperature rise

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Clouds can get in the way of sunlight. Researchers are exploring "what-if" scenarios on the effects of engineered ways to block sunlight.

Results: Exploring sunlight reduction in a computer model that followed emissions' effect on climate produced a new study by researchers from Pacific Northwest National Laboratory. When scientists examined the impact of temporarily reducing the amount of sunlight reaching the Earth, they found that drastic steps to cool the Earth would only be necessary if the planet heats up easily with added greenhouse gases. The analysis published in Climatic Change might help future policymakers plan for a changing climate.

Why It Matters: This new research shows there is a fundamental connection between the need for emissions reductions and the potential need for some sort of solar dimming. This study will also help decision-makers evaluate the amount of solar reduction that might be needed, if it comes to that.

"It's a what-if scenario analysis," said Dr. Steven J. Smith, lead author and senior scientist working at the Joint Global Change Research Institute. "The conditions under which policymakers might want to manage the amount of sun reaching Earth depends on how sensitive the climate is to atmospheric greenhouse gases, and we just don't know that yet."

For more information, see the PNNL News Center, "Earth sunblock only needed if atmosphere warms easily."

Methods: The analysis started with computer-based scenarios that describe different potential pathways to reduce greenhouse gas emissions, which limits the amount of heat in the Earth system due to greenhouse gas accumulation. The researchers combined these scenarios with solar radiation management, a type of geoengineering that might include shading the Earth from the sun's heat by either brightening clouds, mimicking the atmospheric cooling from volcanic eruptions, or putting mirrors in space.

Acknowledgments: This research has been funded by the Fund for Innovative Climate and Energy Research (FICER) at the University of Calgary with additional support from the Pacific Northwest National Laboratory and performed by Drs. Steven J. Smith and Phil Rasch at PNNL. The Joint Global Change Research Institute is a partnership between Pacific Northwest National Laboratory and the University of Maryland.

Reference: Smith SJ and PJ Rasch. 2012. "The Long-Term Policy Context for Solar Radiation Management." Climatic Change DOI:10.1007/s10584-012-0577-3.