PNNL

The Science

The Energy Exascale Earth System Model (E3SM) is a state-of-the-art Earth system model that simulates how Earth’s climate responds to various influences, including atmospheric concentrations of carbon dioxide gas (CO₂). However, accurately predicting the amount of CO₂ in the atmosphere requires simulating how much CO₂ is removed from the atmosphere by forests, other land ecosystems, and the ocean. A group of researchers used E3SM to simulate how land and ocean ecosystems take up carbon dioxide gas from the atmosphere and how various factors, including temperature and precipitation patterns, nutrient availability, and land cover, affect this uptake. This massive effort required scientists from five national laboratories and two universities to overcome the numerous challenges involved in developing and testing new features of the model, carrying out the simulations on major supercomputer platforms, and evaluating the model’s prediction through comparisons with a large suite of observations.

The Impact

Including climate-ecosystem interactions in E3SM enables researchers to study past and future changes in carbon dioxide storage in natural ecosystems. For example, the model allows for analysis of the occurrence and impact of wildfires and droughts—recent causes of major property damage across Australia and the western United States. Ongoing work to extend the model to include representations of energy systems will enable scientists to use E3SM to answer questions like: “How does climate impact energy use and the availability of energy resources such as wind, hydroelectric, and solar power?”

Summary

Changes in climate and rising CO₂ concentrations can alter the amount of carbon taken up by Earth’s ecosystems. For example, warming temperatures that increase plant growth and higher CO₂ concentrations “fertilize” plants can enhance CO₂ uptake from the atmosphere. However, droughts reduce plant growth and wildfires damage forests, resulting in diminished CO₂ uptake or releasing stored CO₂ into the atmosphere.

By simulating these effects, the enhanced E3SM enables researchers to understand and quantify potential changes in CO₂ based on future conditions. The simulations begin in 1850, before the industrial revolution, and simulate the Earth system’s responses to human activities, including industrial emissions, deforestation, and agricultural expansion. The team focused on modeling atmospheric CO₂ removal by plants through photosynthesis and then determining if it remained stored in plants, soils, and wood products, or was released back to the atmosphere through microbial decomposition with climate warming and land use and land cover changes. Using satellite observations and other datasets, the team showed that the model better simulated land ecosystem behavior than older, similar models.

Researchers submitted a subset of the simulations to an international model comparison effort to help the scientific community assess how much is known, and what still remains to be learned, about the simulation of ecosystem-climate interactions.

PNNL Contacts

L. Ruby Leung, PNNL institutional PI, PNNL Atmospheric Sciences and Global Change Division, Ruby.Leung@pnnl.gov 

Susannah Burrows, Lead author, PNNL Atmospheric Sciences and Global Change Division, Susannah.Burrows@pnnl.gov

Kate Calvin, Group Lead, E3SM Biogeochemical Cycles group, PNNL Joint Global Change Research Institute, Katherine.Calvin@pnnl.gov

Funding

This research was supported as part of the Energy Exascale Earth System Model project, funded by the U.S. Department of Energy (DOE), Office of Science, Biological and Environmental Research program. Additional support was provided by the Reducing Uncertainties in Biogeochemical Interactions through Synthesis and Computation Scientific Focus Area, which is sponsored by the Regional and Global Model Analysis Program in the Climate and Environmental Sciences Division of the Biological and Environmental Research program in the DOE Office of Science. Simulations described in this work, and most developmental simulations leading up to them, relied on computational resources provided by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the DOE under contract no. DE-AC02-05CH11231. Computing resources were provided through the DOE Office of Advanced Scientific Computing Research Leadership Computing Challenge.