Principal Investigator

At a Glance

Stephen Pacala organized and initiated a new effort entitled the Net-Zero America Project (NZAP) described in the previous highlight. The project aims to provide policy makers with the necessary analyses to determine a pathway to net-zero greenhouse emissions in the United States. The outcomes of the work are already informing a new National Academies of Science, Engineering and Medicine Committee to which Pacala was appointed chair. The Pacala laboratory also continued its past efforts to improve modeling of the global carbon cycle and terrestrial biosphere.


Research Highlight

During the past year, Pacala recruited Eric Larson, Chris Greig and Jesse Jenkins as the project’s PIs, and met periodically with the team throughout the year to review progress and help steer strategy. NZAP is reviewed in full elsewhere (see pages 15-19) in this report. When the first phase is finished later this year, NZAP will focus on a host of real-world questions about any transition to net-zero. How much will each alternative cost? What infrastructure must be constructed and on what schedule? How many miles of pipe and electrical transmission lines? How much steel and aluminum? How many gas plants with carbon capture and sequestration (CCS), nuclear plants, wind turbines and commercial solar projects? How many residential heat pumps and electric car recharging stations? How much newly planted forest? How many people must be trained and hired? How many jobs would be created and lost? What regulatory burdens and other barriers must be overcome?

Pacala was selected as Chair of a complementary effort by the National Academies of Science, Engineering and Medicine, which began in March, 2020. Unlike NZAP, which explicitly steers clear of both normative statements and policy analysis, this effort focuses on policy and societal impacts as well as on the techno-economic dimensions. The Academies’ effort has already benefited from the techno-economic assessments developed by NZAP. These allow it to concentrate efforts on policy and societal impacts, which will be pivotal in any policy debate.

NZAP has also uncovered a critical need for open-access software tools to help governments and companies plan and understand the transition to net zero. CMI will devote substantial effort over the next five years to produce new software tools.

Pacala’s laboratory also continued its past efforts to advance modeling of the global carbon cycle and terrestrial biosphere. The goal of this work is to improve climate predictions and to reduce uncertainty about the emissions cuts needed to stay beneath a temperature target. Both will reduce uncertainty and improve understanding of environmental impacts of natural carbon solutions.

In addition, Pacala’s group and GFDL researchers published a new and improved land component of the GFDL Earth System Model, which has now participated in the model-comparison for the next IPCC report (CMIP6). They also published two papers on improvements that make the model much better at representing tropical rain forests (led by CMI postdoctoral fellow Isabel Martinez Cano). Pacala’s group also continued work on worrisome data indicating that vines may be taking over tropical rainforest worldwide, which would have a serious impact on atmospheric CO2 (led by CMI postdoctoral fellow Marco Visser). They demonstrated a progressive shift to vine-dominated forest in Panama and are still working on a global assessment using remote sensing.

Finally, as the land components of Earth System Models have gained realism, they have started to predict one of the most obvious features of the biosphere – the coexistence of many plant species in the same location – despite not being explicitly designed to do so. This development is analogous to the spontaneous emergence of the ENSO (El Niño and La Niña) or hurricanes in ocean-atmosphere models, once the grid resolution became sufficiently small. It offers the intriguing possibility of attacking the climate and biodiversity problems with a single integrated modeling tool. Pacala and CMI postdoctoral fellow Matteo Detto are following this line of investigation by studying the coexistence phenomenon mathematically.

Figure 2.1.
A new model for the land surface, including land use and the terrestrial carbon cycle, was implemented in GFDL’s Earth System Models this year. CMI has been investing in this effort consistently for over a decade. The new LM4 model makes predictions across a range of scales. Panels on the right compare global patterns of ecosystem carbon uptake (Gross Primary Production [GPP] in upper right) and carbon storage (lower right). Panels on the left show population-level phenomena: predicted vs. actual tree size distributions (upper left) and competitively dominant plant types (lower left).