Published: Sept. 27, 2013

Changes in the mean and extremes of surface temperatures, from centennial to daily timescales

Martin Tingley, Assistant Professor

Department of StatisticsPenn State University

Date and time: 

Friday, September 27, 2013 - 3:00pm


ECCR 245


Characterizing how the magnitude and frequency of extreme climate events are changing, and will continue to change due to anthropogenic forcing of the climate system, is currently a major challenge for the climate sciences. While the current warming trend is certainly contributing to the recent increase in warm temperature extremes and decrease in cold extremes, far less is understood about the contribution of possible changes in the variability about the central tendency.

This talk investigates the interrelation between changes in the mean and variability of surface temperatures on two distinct time scales. I first present a Bayesian Hierarchical reconstruction of Arctic and sub-Arctic temperature anomalies, showing that a number of summers in the last decade feature conditions that are without precedent in the last 600 years. These recent warm extremes, which exceed in frequency and magnitude those expected from a stationary climate, can be accounted for by a change in the mean temperature alone, with no change in the variance.

The second part of the talk presents a quantile regression analysis of daily summer surface temperatures from 1979 to 2012 over the densely sampled North American region. There is strong heterogeneity in warming trends as a function of percentile, with some regions featuring faster warming for the 95th percentile than for the median, and vice versa. On shorter timescales, changes in both the mean and variability are contributing to changes in warm extremes, with their relative importance varying as a function of space.