Principal Investigator


At a Glance

Stephen Pacala is responsible for founding the Princeton Net-Zero America Project. This project seeks to develop technological pathways to decarbonize the U.S. economy by mid-century. Pacala also chaired a National Academies of Sciences, Engineering and Medicine committee to develop a policy manual for the U.S. to transition to net-zero emissions of all greenhouse gases by 2050. In addition, the Pacala group created a model that provides a valuable tool to predict root proliferation in global earth-system models, which is critical to predicting ecosystem carbon storage.

 


Research Highlight

CMI Principal Investigator Stephen Pacala helped steer the Net-Zero America Project in the first few months of 2020. He focused on land-based mitigation measures aimed at curbing greenhouse gas emissions (see page 16). This research outlines five distinct technological pathways for the United States to decarbonize its entire economy. The research is the first to quantify and map, with this degree of specificity, the infrastructure that needs to be built and the investment required to run the country without emitting more greenhouse gases into the atmosphere than are removed from it each year. It is also the first to pinpoint how jobs and health will be affected in each state at a highly granular level, sometimes down to the county.

Net Zero America text with light map of US
The Net-Zero America Project seeks to develop technological pathways to decarbonize the U.S. economy by mid-century

In a separate effort, Pacala was appointed chair of a National Academies of Sciences, Engineering and Medicine committee to produce a policy manual for the U.S. to transition to net-zero emissions of all greenhouse gases by mid-century. The Committee was directed to review everything written about the transition, and to obtain testimony about work in progress. The report is entitled “Accelerating Decarbonization in the United States: Technology, Policy and Societal Dimensions.” It provides both a portfolio of recommended policies for technical aspects of the transition, and the policies needed to ensure that the transition is fair and just. The team took the words “fair and just” to mean that the net-zero energy system should eliminate the historical environmental injustices built into the current energy system. This includes efforts to alleviate the adverse impacts of fossil fuels falling disproportionately on low income and historically marginalized Americans, and to attempt to mitigate or prevent the impacts of fossil-associated job losses for workers and their communities.

Accelerating Decarbonization of the U.S. Energy Systems poster
CMI director, Stephen Pacala, chaired a National Academies of Sciences, Engineering and Medicine committee to develop a policy manual for the U.S. to transition to net-zero emissions of all greenhouse gases by 2050.

It is very important to understand that the CMI did not fund Pacala’s involvement in the Academies’ effort. Pacala withdrew from active research with the Net-Zero America Project, after having been appointed Chair of the Academies’ effort, in order to keep a completely open mind. At the same time, the work on the Academies’ report, which was released February 2, 2021, convinced Pacala that the human dimensions of the net-zero problem will likely prove even more important than technical or cost hurdles. Reactions from lawmakers since the release of the Academies’ report confirm this conclusion and have shaped Pacala’s resolve to pursue the determinants of public acceptance in future CMI work. As one example, where fossil jobs are relatively abundant, renewables jobs will not compensate for future fossil job losses. However, net-zero industrial jobs could. For instance, it might be possible to build a national CO2 pipelines network by starting with net-zero industrial hubs in regions of high fossil employment. This would connect industry to sequestration sites and create an employment boom before the job losses occur. The Net-Zero America team is currently analyzing such a system.

Among other CMI research pursued by the Pacala team over the past year was an effort led by Pacala graduate student, Ciro Cabal. The team’s findings, published December 2020 in Science, shed light on the underground life of plants, particularly on improving an understanding of how plant roots store carbon. To investigate, the researchers grew pepper plants alone and with neighbors, and stained the roots of neighboring plants (by injection) to distinguish which roots belonged to which plant. They found that the energy a plant devotes to its roots depends on proximity to other plants: when close together, plants heavily invest in their root systems to compete for finite underground resources; if far apart, they invest less. As about a third of the world’s vegetation biomass (and therefore carbon) is below ground, this model provides a valuable tool to predict root proliferation in global earth-system models.

Orange, Blue, Red, and light blue plant roots
The Pacala team published findings in Science shedding light on the underground life of plants, particularly improving an understanding of how plant roots store carbon. (Photo by Ciro Cabal, Princeton University Department of Ecology and Evolutionary Biology)