Atmospheric Composition and Climate Change: A Tale from Two Climate Models

Event type: 
21 August 2014

Climate Change Research Centre seminar room, Mathews Building, Kensington Campus, Sydney

V. "Ram" Ramaswamy
Director, NOAA/Geophysical Fluid Dynamics Laboratory, Princeton University
Climate Change Research Centre

Atmospheric Composition and Climate Change: A Tale from Two Climate Models

Utilizing the two climate models “CM2” and “CM3”  developed at NOAA’s Geophysical Fluid Dynamics Laboratory over the past decade and used, respectively, in the Intergovernmental Panel on Climate Change Fourth (2007) and Fifth (2013) Assessments, we discuss the features concerning atmospheric composition, focusing particularly on the short-lived aerosol species and their effects on climate. Included in this analysis are the manner of treatment of the human-influenced greenhouse gas and aerosol emissions and the physical characteristics, with extensive comparisons against observations revealing strengths, weaknesses, and gaps in understanding. The two models differ in their treatment of the aerosol interactions with clouds, and this manifests in a contrast in the models’ simulations of the 20th century climate change. However, there is a clear picture emerging from both models about the impact of aerosols in the 21st century climate change projections. Both the “direct” effects of aerosols and the “aerosol-cloud interaction” effect play a substantial role in the global climate forcing and response. The North-South hemispheric asymmetry in climate forcing that arises for aerosols relative to the well-mixed greenhouse gases affects significantly the anthropogenic changes induced in the tropical circulation pattern and the atmosphere and ocean heat transports.

About the speaker:

Ram became the fourth Director of NOAA's Geophysical Fluid Dynamics Laboratory in 2009. Ram was named Acting Director of the laboratory in 2007. Previously, he served as leader of the Atmospheric Physics and Chemistry group and senior scientist, after joining the GFDL research staff in 1987.

Under his leadership, a new era in supercomputing was launched for GFDL. Significantly enhanced computing power has enabled higher resolutions and greater complexity in the lab's climate models. GFDL now routinely runs experiments using very high resolution global climate models, capable of revealing regional details. The lab's new Earth system models simulate the interaction of biogeochemical cycles (including human influences) with the climate system. Future projections from these models produce a level of detail and realism not previously possible.

Since 1992, Ram has been a Lead Author or Coordinating Lead Author for each of the assessment reports for the Intergovernmental Panel for Climate Change. He has continued to have a leading role in the Global Change Research program, and served on the Joint Scientific Committee, including as Vice-Chair, of the World Climate Research Program. Ram is a Fellow of the American Geophysical Union and the American Meteorological Society, and he has received the World Meteorological Organization's Norbert Gerbier MUMM International Award three times. Ram has also received numerous other awards, including the Department of Commerce Gold Medal, twice, and the Presidential Rank Award.

Ram's research career has focused on improving our understanding of atmospheric physics and the roles of natural and human-influenced factors driving climate change, by developing and using state-of-the-art climate models. His published research includes over 150 papers in refereed journals. Ram teaches atmospheric radiation with applications to climate in the Atmospheric and Oceanic Sciences Program at Princeton University, and he has mentored graduate students, postdoctoral and visiting scientists.

Ram received his Ph.D. in Atmospheric Science from State University of New York at Albany, and bachelor's and master's degrees from the University of Delhi, India.