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Climate expert discusses geoengineering with House

The science and technology of preventing sunlight from reaching earth's surface

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February 04, 2010 Share This!

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WASHINGTON — Philip Rasch, chief scientist for climate science at the Department of Energy's Pacific Northwest National Laboratory in Richland, Wash. testifies today before the House Committee on Science and Technology's Subcommittee on Energy and Environment on Solar Radiation Management — approaches for managing the amount of sunlight reaching the Earth's surface to counter some of the effects of global warming.

He will testify as part of a hearing titled "Geoengineering II: The Scientific Basis and Engineering Challenges."

Geoengineering is the intentional modification of the earth's climate. Specifically, Rasch will cover current scientific understanding of such aspects of solar radiation management as:

  • How aerosol particles introduced into the lower and upper atmosphere might affect global warming and weather, both globally and locally
  • The limitations of what scientists know and how to invest research dollars
  • How much the methods might cost and how long the effects could last.

"I recognize that geoengineering is a very controversial and complex subject, and that there are many issues associated with it of concern to scientists and society," Rasch wrote in his prepared testimony. "Scientists interested in geoengineering want to be responsible and transparent. We care about doing the science right, and in a responsible way."

Rasch will discuss two methods of "managing solar radiation": 1) the production of sulfate aerosols in the upper atmosphere and 2) the possibility of spraying tiny drops of seawater near the surface of the earth. Sulfur dioxide injected into the upper atmosphere where clouds rarely form, called the stratosphere, reacts chemically with other gases up there and creates small sulfate particles. The particles scatter incoming sunlight and prevent it from warming the lower atmosphere.

The seawater tactic involves spraying seawater from specially designed ships into the sky. The salty water increases the number of cloud drops and decreases the size of each droplet in clouds in the troposphere — the part of the atmosphere down here that supports life. Clouds made up of more and smaller droplets reflect more sunlight than those with larger droplets.

He will discuss the effect that these approaches might have on atmospheric temperatures, local climate and weather, and how long they might need to be used to get the desired lowering of temperatures and also the risks associated with these strategies.

Rasch will also discuss the potential costs associated with deploying and monitoring the approaches. He will also point out areas where the scientific understanding is weak, and recommend how much research needs to be done. Rasch will also address how to clean up any environmental after-effects.

About Philip Rasch

Philip Rasch serves as the chief scientist for climate science at the Pacific Northwest National Laboratory. He oversees more than 90 researchers who focus on climate, aerosol and cloud physics; global and regional scale modeling; integrated assessment of global change; and complex regional meteorology and chemistry. Rasch is particularly interested in the role of aerosols and clouds in the atmosphere, and on their impact on climate. For the last five years, he helped to lead the technical development team for the next generation of the atmospheric component of the Community Climate System Model Project, one of the major climate modeling activities in the United States. Rasch was a chair of the International Global Atmospheric Chemistry Program (IGAC, 2004‐2008), and participates on the steering and scientific committees of a number of international scientific bodies. He has contributed to scientific assessments for the World Meteorological Organization, NASA and the Intergovernmental Panel on Climate Change.

The hearing was held in Room 2325 of the Rayburn House Office Building at 10 a.m. EST Thursday February 4. More information is available at

A PDF version of the testimony is available upon request.

Tags: Environment, Fundamental Science, Climate Science, Atmospheric Science, Aerosols

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