Branwen Williams, Scripps College – Global Warming

On Scripps College Week:  How much of recent global warming would have happened without humans?

Branwen Williams, associate professor of environmental science, looks into the data to find the answer.

Dr. Branwen Williams’s research develops the techniques that we use to generate records of our past ocean and climate variability, and uses these records to understand mechanisms driving environmental changes.  She got her B.Sc. in Marine and Freshwater Biology at the University of Guelph.  She then got her M.Sc. in Biology at GEOTOP with the Université du Québec à Montréal.  She then went to complete at her Ph.D. in Geological Science in the School of Earth Sciences at the Ohio State University.  From there, she did a postdoctoral research fellowship in the Department of Chemical & Physical Sciences at the University of Toronto Mississauga.  She is now an Associate Professor of Environmental Sciences in the W.M. Keck Science Department , a science department that is shared among three colleges of the Claremont Colleges: Claremont McKenna College, Pitzer College, and Scripps College.

Global Warming


The carbon released with fossil fuel use changes our climate, although our climate would also change naturally, even if, people weren’t around.  My research focuses on understanding how much of the recent, very rapid warming that we have been experiencing is caused by people and how much would have occurred in our absence.  This helps us better understand how the climate will continue to change in the future.

We focus on finding environmental data from locations or periods in time when we didn’t have instruments measuring for us, like ocean temperatures before we had thermometers.  To find the data, we measure the growth and chemistry of marine plants. These plants, like some trees, form a growth ring in their skeleton each year.  By counting these rings we can identify time in the skeleton, how long the plant has been growing for, and when each year of growth occurred. These plants also encode characteristics of the surrounding environment into the chemistry of each growth ring when it is formed, for example, whether that year was warmer or cooler.  Some of these plants in the ocean can live for hundreds of years, and throughout their entire life they are documenting and preserving in their skeleton these changes in seawater temperature.  We collect the specimens, measure the chemistry of each growth ring, and then create records of past changes in seawater temperature.

Our research shows the recent warming is really unusual, particularly how fast and how widespread it is. When we combine our data with computer simulations of all the things that cause temperature to change, we find that at least half of the warming over the past century is caused by people.  This means that as we continue to use fossil fuels, global warming will rapidly continue. However, if we reduce our use of fossil fuels, we can slow the rate of warming by a lot.