Free-Air Carbon Dioxide Enrichment (FACE) Experiments

Free-Air Carbon Dioxide Enrichment (FACE) Experiments

Located at the Harshaw Experimental Forest near Rhinelander, Wisconsin, the Aspen FACE Experiment operated as a DOE User Facility, and was a collaborative effort among 11 organizations.

Since the mid-1990s, the U.S. Department of Energy (DOE) supported large-scale experiments to study how ecosystems respond to changing atmospheric conditions. Through the Terrestrial Carbon Processes Program and the Program for Ecosystem Research, DOE funded two major types of trace gas enrichment experiments:

  • Free-Air Carbon Dioxide Enrichment (FACE) experiments
  • Open-Top Chamber (OTC) experiments

Initially, FACE sites were developed as research and development platforms, later evolving into environmental research user facilities open to the broader scientific community. DOE’s Biological and Environmental Research (BER) program operated four FACE facilities distributed across the United States. Brookhaven National Laboratory provided central operations and coordination for several FACE sites. BER also supported OTC experiments in partnership with the Smithsonian Environmental Research Center in Maryland and Florida.

Together, these projects contributed to a global network of FACE experiments, connecting U.S. research efforts with international studies to better understand carbon, nutrient, and water cycles across ecosystems.

Data Archive and Repository

The Carbon Dioxide Information Analysis Center (CDIAC) served as the central data repository and archive for DOE-supported FACE and OTC research. The FACE Data Management System ensures that datasets are openly available and accessible to researchers worldwide, supporting cross-site data analysis and synthesis.

As part of this system, CDIAC:

  • Conducted quality assurance and control (QA/QC) on submitted data
  • Reviewed and standardized documentation
  • Researchers can visit individual site pages for more detailed information and direct data access.
  • All of these datasets are now archived and made available on the ESS-DIVE data repository.

DOE Research Network

These projects are part of the CO₂ research network supported by the Global Change and Terrestrial Ecosystems core project of the International Geosphere-Biosphere Programme. Results from the experiments contribute to the Terrestrial Ecosystem Response to Atmospheric and Climatic Change initiative, a five-year effort that integrates experimental data and global change modeling.

Illustration of FACE MDS Ecosystem

The Free Air CO₂ Enrichment Model-Data Synthesis (FACE-MDS) project was created in 2008 with support from the National Center for Ecological Analysis and Synthesis. Since 2011, the FACE-MDS has been funded by the U.S. Department of Energy’s Office of Science through the Biological and Environmental Research program.

The project’s initial goal was to benchmark model predictions of how ecosystems respond to elevated atmospheric CO2. Initially we used data from two of the most comprehensive long-term studies of forest and ecosystem responses to higher CO₂ levels: the Duke and Oak Ridge FACE experiments. As the project evolved, the focus shifted towards uncovering the underlying assumptions that shape model behavior, developing an approach called assumption-centered modeling. We also expanded the sites in the analysis to include the Rhinelander FACE site, the Kennedy Space Center OTC experiment in a scrub-oak ecosystem, and the Prairie Heating and CO2 Enrichment (PHACE) experiment in a short-grass steppe ecosystem.

FACE MDS Group Photo

Over the years, FACE-MDS has brought together scientists from over 35 institutions across the U.S. and internationally. The project is led by principal investigators at Oak Ridge National Laboratory in the United States, with key partners at the Hawkesbury Institute for the Environment in Australia, the Max Planck Institute for Biogeochemistry in Germany, and the University of Bristol in the UK.

This international effort continues to strengthen global understanding of how atmospheric CO₂ affects plants, ecosystems, and Earth systems. The FACE-MDS project and team has advanced understanding of how terrestrial ecosystems respond to elevated atmospheric CO2, identified areas where models can be improved, highlighted new questions for future research, and set a new standard for comparing ecosystem models with experiment observations across the scientific community.

For questions about the work, contact Anthony Walker.

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