Geoengineering: Science and Governance
Phil Rasch, Chief Scientist for Climate Science, Pacific Northwest National Laboratory, "Exploration of Marine Cloud Brightening"
Phil Rasch, Ben Kravitz, and Hailong Wang
Latham (1990) suggested that marine clouds might be used to cool the planet by deliberately introducing additional aerosols over the ocean surface to increase cloud albedo, and possibly cloud lifetime and extent, based upon ideas initially advanced by Twomey (1974, 1977). Theory, and simple parcel model calculations indicate that adding additional aerosols ought to "brighten" (increase the albedo of) clouds, and the idea has come to be known as Marine Cloud Brightening (MCB). Observations, and more detailed process-oriented models [Cloud Resolving Models (CRMs) and Large Eddy Simulation (LES) models] hint that treating processes neglected in early studies make the situation more complicated. Early LES studies by Wang et al. (2009, 2011) showed that internal cloud dynamics play a role, and that the cloud response is strongly dependent upon dynamical regime, aerosol injection strategy, and ambient background aerosol amount among other factors. These studies suggest that the processes that are important are not yet explicitly treated in general circulation cloud models, and their neglect may lead to an over-prediction of the efficacy of aerosol injections for MCB. The focus of previous MCB studies with CRM/LES models has been on liquid, marine stratocumulus clouds. We recently started an initial exploration of MCB strategies on mixed-phase (ice and supercooled liquid) mid- and high-latitude clouds. The issues are interesting and relevant to understanding aerosol-cloud interaction on a fundamental climate level. In this presentation I will review some of our LES modeling work on aerosol injections and mixing in the stable high-latitude boundary layer and their impact on mixed-phase clouds, and connect them to recent and proposed observations and field experiments, and to global modeling studies.
Finding safe, secure alterative ways to combat climate change requires exploration and innovation. Join us to learn more about this topic from leading climate engineering researchers. Sponsored by HUCE and the MIT Joint Program on Global Change
Dr. Philip Rasch serves as the Chief Scientist for Climate Science at the Pacific Northwest National Laboratory (PNNL), a Department of Energy Office of Science research laboratory. In his advisory role, he provides leadership and direction to PNNL's Atmospheric Sciences and Global Change (ASGC) Division. The Division conducts research on the long‐term impact of human activities on climate and natural resources using a research strategy that starts with measurements and carries that information into models, with a goal of improving the nation's ability to predict climate change.
Dr. Rasch provides oversight to more than 90 researchers who lead and contribute to programs within a number of government agencies and industry. These programs focus on climate, aerosol and cloud physics; global and regional scale modeling; integrated assessment of global change; and complex regional meteorology and chemistry.
Dr. Rasch received a Bachelor Degree in Atmospheric Science and another in Chemistry from the University of Washington in 1976. He then moved to Florida State University for a Master of Science in Meteorology. He went to the National Center for Atmospheric Research (NCAR) in Boulder, Colorado as an Advanced Study Program (ASP) Graduate Fellow to complete his PhD (which was also awarded from Florida State University). Following his PhD, Rasch remained at NCAR, first as ASP Postdoctoral Fellow, and then as a scientist where he worked in various positions. He joined PNNL in 2008. Rasch also holds an adjunct position at the University of Colorado and is an Affiliate Professor in the Department of Atmospheric Science at the University of Washington.
Dr. Rasch is internationally known for his work in general circulation, atmospheric chemistry, and climate modeling. He is particularly interested in the role of aerosols and clouds in the atmosphere, and has worked on the processes that describe these components of the atmosphere, the computational details that are needed to describe them in computer models, 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. He also studies geoengineering, or the intentional manipulation of the atmosphere to counteract global warming.
Dr. 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 was named a fellow of the American Association for the Advancement of Science, recognized for his contributions to climate modeling and connecting cloud formation, atmospheric chemistry and climate. He has contributed to scientific assessments for the World Meteorological Organization, NASA and the Intergovernmental Panel on Climate Change.