Scott Lehman (INSTAAR)

INSTAAR Seminar Series
Hybrid event, in person and via Zoom
Afterwards, we have scheduled time for Dr. Lehman to informally chat with graduate students and early career scientists.

Location:
Sievers Conference Room (SEEC S228)
4001 Discovery Drive, Boulder, CO

Audience:
All are welcome: please email instaar@colorado.edu for Zoom link and password if you'd like to attend virtually.

Graduate students and early career scientists:
After the talk we have scheduled time for an informal chat with Dr. Lehman. Take advantage of this opportunity to ask questions about Dr. Lehman’s prolific career and his journey in science! Please feel free to forward this to colleagues who may be interested in attending.

Abstract:
I will summarize our efforts to represent the global tropospheric ¹⁴CO₂ budget and distribution and their implications regarding the magnitude and age distribution of heterotrophic respiration and (in this example, US) emissions of CO₂ derived from fossil fuel use and cement production. Unlike the atmospheric budget of CO₂ which is controlled by net CO₂ fluxes associated with uptake and release by the land biosphere and oceans and from fossil fuel combustion, the ¹⁴CO₂ budget is additionally influenced by much larger gross (one-way) land and ocean fluxes with ¹⁴C content very different from the contemporary atmosphere. These so-called “disequilibrium isofluxes”, along with ¹⁴C-free emissions from fossil fuel use and pure isotopic fluxes from cosmogenic production, dominate the atmospheric ¹⁴CO₂ budget. We proceed by constructing 1°x1° gridded estimates for each of these terms for the period 2000-2012 and optimize the flux balance by comparison to observations of the atmospheric inventory of CO₂ and the year-to-year change in global mean D¹⁴C. We then carry the optimized gridded fluxes in the TM5 transport model for comparison to a global array of D¹⁴C observations. Based on the apparent ability of the model to represent the measurements, we develop and apply a dual-tracer (D¹⁴C+CO₂) inversion system that simultaneously solves for fossil CO₂ emissions and Net Ecosystem Exchange. Although our analytical framework is global, we will focus on the US over which we have the greatest number of ¹⁴C observations. This work provides for the first-ever “top down” estimates of anthropogenic CO₂ emissions for any country and will add to the US contribution to the UNFCCC-mandated Global Stocktake summarizing a decade of national emissions.