Environmental & Climate Sciences Department Seminar

Changes in the composition of the atmosphere cause changes to the planetary radiation budget to which the Earth responds by changing its temperature; changes in temperature may also change the atmosphere's opacity in ways that damp or amplify the temperature change. This framework — radiative forcing, adjustments, and feedbacks — provides a useful lens though which to think about future atmospheric conditions and allows us to use the Earth's past and present-day behavior as a guide to the future. A focus on adjustments, including aerosol-mediated changes to clouds, also highlights challenges and opportunities for process-based modeling, data assimilation and state estimation, and satellite observations.

In this talk I'll focus on understanding the radiative forcing to which the earth has been subject over the course of industrialization. I'll describe an effort to provide highly-accurate estimates of instantaneous radiative forcing by greenhouse gases across a wide range of scenarios, and highlight how efforts to compute adjustments inevitably dominate the uncertainty in effective radiative forcing. Developing an understanding of real-world forcing also lets us understand the surprisingly wide range of forcings reported by climate models for the same change in atmospheric composition, highlighting the difference between model diversity and true uncertainty.