Start Date/Time: Tuesday, October 19, 2010, 2:30 PM
Location: A-118 UW Physics/Astronomy Auditorium (PAA)
James F. Kasting, Ph.D.
Professor of Geosciences
Pennsylvania State University, University Park
Abstract: Earth's climate has remained relatively warm during most of its history even though the Sun was considerably fainter in the distant past. Higher concentrations of greenhouse gases, especially CO2, CH4, and NH3 (shielded by fractal organic haze), in the past are probably required to explain this warmth, although albedo feedbacks could have played a role, as well. The recent paper by M. Rosing et al. (Nature, 2010) suggests, surprisingly, that atmospheric CO2 concentrations during the Archean Era were no more than 3 times higher than today, based on analysis of banded iron-formations, and that cloud feedbacks caused by changes in biogenic sulfur gas fluxes were the key to keeping the Earth warm. I will argue that Rosing et al. are wrong and that atmospheric CO2 concentrations were considerably higher than they specify.