K.D. Nelson Lecture Series – Dr. Angeline Pendergrass

The Department of Earth & Environmental Sciences in the College of Arts and Sciences presents the K.D. Nelson Lecture Series featuring  speaker Dr. Angeline Pendergrass of Cornell University. Her talk is titled: The Implications of Time Varying Climate Feedbacks for Precipitation.

Climate sensitivity varies on multiple timescales with different magnitudes as climate feedbacks evolve over time. This timescale dependence of climate feedbacks can be understood through the radiative fluxes at the top of the atmosphere. If TOA fluxes respond on multiple timescales, then surface fluxes may as well, which would lead to timescale dependence of global mean precipitation. Dr. Pendergrass’ and team investigate whether it does in millennial-length simulations of the response to abrupt increase in carbon dioxide from LongRunMIP.

In order to compare the slope of precipitation versus temperature (also known as “hydrologic sensitivity”) among timescales, this slope must be calculated first. Ordinary least squares, the most common regression technique often used by default for calculating a slope, provides (on average) the correct slope of a trend over time. But, when regressing against an independent variable with internal variability, such as temperature, it systematically underestimates the slope (called “regression dilution”). This is well known to statisticians, and at least beginning to be appreciated in climate science. And still further problems can arise of the variability between variables is correlated. Dr. Pendergrass introduces a new approach to quantify these biases specific to the climate context. She applies them to investigating the time-dependence of climate sensitivity and hydrologic sensitivity.