Welcome to the Washington/Northern Virginia Chapter of IEEE/GRSS

Technical Meeting

Wednesday, June 4, 2008 at 3:30pm

NASA Goddard Visitor Center

(refreshments available at 3:00pm)



Dr. Robert F. Cahalan

Head of the Climate and Radiation Branch

NASA Goddard Space Flight Center, Greenbelt, MD

Earth's Changing Climate - What's been happening in recent decades? What might we do about it?

Abstract: The evidence that Earth has been warming primarily due to increased emission of greenhouse gases from human activity is presented in the context of natural climate forcings due to volcanoes, solar activity, and natural variability. We introduce components of the "Global Earth Observing System of Systems" (GEOSS) that is now revealing regional climate changes and their interconnections in unprecedented detail and precision. We consider the data that was used by the 4th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, see http://www.ipcc.ch/), that received the 2007 Nobel Peace Prize along with Albert Gore, Jr. We primarily focus on the scientific basis of the IPCC report from Working Group 1 (WG1), and emphasize the primary uncertainties that limit our capability to predict the timing of changes in the polar icecaps, in rainfall, and in other key climate variables. These include uncertainties due to aerosols and clouds that are the main focus of the Climate and Radiation Branch at Goddard, and also a priority of the United States Climate Change Science Program that coordinates the research of NASA with 12 other federal agencies. I also consider the other two IPCC reports, on adapting to climate change (WG2) and on mitigating climate change (WG3). Here I give my personal opinion of a likely scenario in which we may begin to meet the challenge of 21st century climate change.


Dr. Robert Cahalan is Head of the Climate and Radiation Branch at NASA/Goddard, which he joined in 1979, coming from NCAR in Boulder CO. He is also Visiting Senior Research Scientist at UMCP/ESSIC, Adjunct Professor of Physics at UMBC, Lead Scientist for THOR lidar, Chair of the 3DRT Working Group of the International Radiation Commission, NASA Project Scientist for the EOS SORCE mission that launched in January 2003, Project Scientist of the International Intercomparison of 3D Radiation Codes (I3RC), and NASA representative to the U.S. Climate Change Science Program (CCSP = USGCRP + CCRI), where he chaired the Observations Working Group. He is a member of the DoE ARM Science Team, and the NASA EOS-Landsat Science Team. Dr. Cahalan has been a graduate advisor at universities in the USA, Canada, and the Netherlands, and Visiting Scientist at NCAR, Aspen Center for Physics, Institute of Theoretical Physics in Warsaw, and ECMWF in Reading, England. Dr. Cahalan's research focuses on climate and cloud structure, developing retrieval techniques that extend the "independent pixel approximation" (IPA) by use of 3D transfer methods, and parameterizations such as the "effective thickness approximation" (ETA) that relate cloud optical properties to cloud structure. With colleagues at GSFC and LANL Dr Cahalan led development of a new measurement approach "Thickness from Offbeam Returns," realized in Goddard's innovative THOR lidar system that combines a multiple field-of-view wide-angle receiver with 3D retrieval methods to determine the thickness of optically thick cloud layers. THOR is now being adapted to measure thickness of snow and sea ice layers. Dr. Cahalan directs the Intercomparison of 3D Radiative Codes (I3RC) that has developed a set of benchmarks used to certify 3D radiative transfer codes, and is now coordinating a community 3D coding effort.