Carbon, Climate, my Career, and the Prospect of Being Replaced by Linear Regression

May 09, 2024

Scott Denning

Hosted by Department

Abstract

I wanted to be an astronomer when I was a kid, but switched to geology in college. I worked briefly in the oil industry in the 1980s then lost my job when the industry collapsed in 1985. I started at CSU in 1986 working on the chemistry of precipitation and surface waters in Rocky Mountain National Park and carried heavy sampling equipment into Loch Vale 200 Tuesdays in a row! I started taking ATS classes as an employee benefit in 1989, and was a full-time grad student from 1990-1994.

Working with Dave Randall, I was probably the first person to implement photosynthesis and decomposition into a GCM. I moved to UC Santa Barbara in 1996 to start a faculty career but moved back to CSU in 1998 and I've been on the faculty here ever since. I built a big research group here and mentored about 25 grad students. We collaborated with large-scale ecosystem experiments in Wisconsin, Brazil, Iowa, and Oklahoma, understanding and predicting carbon-water-climate interactions at multiple scales. We used spatial data to scale model simulations to regions and then evaluated against atmospheric mass balance of a bunch of biogeochemical tracers.We pioneered the use of global remote sensing to constrain and evaluate coupled carbon-climate models. From 2006-2016 I worked with Dave and Melissa to lead Education and Diversity efforts for CM MAP, which really opened my eyes to the transformative power of engaging a wider audience. Undergraduate teaching and Semester at Sea have both provided spectacular opportunities to carry our fabulous science to young people around the world.

Half the CO2 from burning fossil fuels goes away. It has been my life's work to figure out where it goes, how it gets there, whether it will come back to bite us, and how it interacts with the rest of the climate system. Carbon-climate feedback is among the most uncertain features of 21st Century global change, arguably a bigger problem than aerosol or cloud feedbacks. Over the past 15 years, a remarkable ESM consensus has emerged about an emergent property of the coupled system known by the terrible acronym TCRE - the Transient (climate) Response to (cumulative) Emissions. In virtually every ESM assessed by IPCC, fortuitous cancelation among important processes produces global warming that's linearly proportional to total historical carbon emissions. This remarkable cancellation is surprisingly robust across a gigantic range of future scenarios. I find it hard to believe that I could be replaced by a single line of code, but TCRE has emerged from hundreds of papers by dozens of authors and survived 15 years of rigorous review. It's featured in the Summaries of the AR6 Synthesis.