Speaker:  Prof. Robert Pincus, Lamont-Doherty Earth Observatory at Columbia University, USA

Title: The spectral roots of hydrological sensitivity: why more rain falls at warmer temperatures.

Abstract: Projections of future climate change starting as early as the 1980s have shown that globally-integrated rainfall decreases with carbon dioxide concentrations and increases with surface temperature, though only about 1/3 as quickly as does the concentration of water vapor in the atmosphere. The mechanisms causing this increase have not been fully clear. In this talk I’ll exploit a series of recently-developed theoretical insights to show with pencil and paper that changes in cooling are driven primarily by changes in atmospheric opacity, particularly within the water vapor window. This suggests that changes in mean rainfall are primarily controlled by the thermodynamic and spectroscopic properties of Earth’s main greenhouse gases: water vapor and carbon dioxide. Consistent with comprehensive general circulation models, our results explain why mean rainfall increases with surface warming at about 2\%/K, why this rate is largely unchanged over numerous doublings of atmospheric carbon dioxide, and why rainfall decreases in hothouse climates.  

Short bio:  Robert Pincus is a Lamont Research Professor at the Lamont-Doherty Earth Observatory at Columbia University. He is an atmospheric physicist interested in how clouds, water vapor, and radiation sculpt the circulation of the atmosphere and the thermal and hydrological climate. He has been involved in field measurements of clouds and their environment; in the development and assessment of climate models, especially as related to clouds and radiation; and in the remote sensing of clouds via reflected sunlight. He a Ph.D. in atmospheric sciences from the University of Washington, Seattle. Before his current position, Dr. Pincus spent time at NASA Goddard Space Flight Center as an NRC Resident Research Associate, the University of Wisconsin, Madison, as a Visiting Professor, and  CIRES / University of Colorado, Boulder with a joint appointment at the NOAA Physical Sciences Lab. Serving on many US and international committees and activities around radiative forcing and modeling of climate, he is currently Core Panel Member of the Coupled Model Intercomparision Project (CMIP), and has served as lead coordinator of the Radiative Forcing Model Intercomparison Project (RFMIP), and Leader of the Leveraging the Past Record Initiative of the WCRP Grand Challenge on Clouds, Circulation

Website: https://people.climate.columbia.edu/users/profile/robert-pincus