DOE Scientists Contribute to 5th National Climate Assessment

The United States is taking substantial actions to combat climate change, but Americans are experiencing increased risk from extreme weather events that are exacerbating social inequities.

This is a major conclusion presented in the recently released Fifth National Climate Assessment (NCA5), a product of the U.S. Global Change Research Program (USGRP), comprised of the U.S. Department of Energy (DOE) and 13 other Federal agencies. Program managers and scientists within DOE’s Earth & Environmental Systems Modeling (EESM) program were key contributors to the report. 

NCA5 is an authoritative report on the science of climate change, focusing on the United States, and serves as a foundation for efforts to assess climate-related risks. It also helps inform decisions by policymakers around the country about how to respond to climate change.

“This is the most comprehensive report to date on climate change, which is impacting communities across the United States,” says NCA5 contributing author Paul Ullrich, a climate modeling scientist at Lawrence Livermore National Laboratory and lead of the Program for Climate Model Diagnosis and Intercomparison (PCMDI)—a Regional & Global Modeling Analysis (RGMA) program area project within EESM.

“NCA5 is an effort that details the state of the science related to climate change and the potential impacts for communities across the United States,” says Ullrich, noting that what makes the report unique is the level of detail of impacts across all U.S. regions and territories.

According to Ruby Leung, Battelle Fellow at Pacific Northwest National Laboratory and lead author of the Earth System Processes chapter of the report, NCA5 builds upon the existing body of evidence of human-caused climate change. “It’s important for us to recognize that how much climate change we will be experiencing in the future depends on the choices that we make now,” she says in a November 14, 2023 USA Today article.

Leung is the chief scientist for DOE’s flagship earth system model, the Energy Exascale Earth System Model (E3SM) and a principal investigator on the RGMA project, Water Cycle and Climate Extremes Modeling.

Report key messages published in the NCA5 report include:

• The United States is taking action on climate change. In every region of the country, mitigation and adaptation efforts are underway. Since 2007, emissions, energy intensity, and emissions intensity have decreased while the population and gross domestic product have grown.
• People in the United States are experiencing increased risks from extreme events. Many of the climate conditions and impacts people are experiencing today are unprecedented over thousands of years. People across the United States are experiencing warmer temperatures, longer-lasting heat waves, heavy precipitation, drought, flooding, wildfires, and hurricanes, which are increasing in frequency and/or severity.
• Climate change exacerbates social inequities. Underserved and overburdened communities face disproportionate risks and impacts from climate change, which deepens social and economic inequities and contributes to persistent disparities in the resources needed to prepare for, respond to, and recover from climate impacts.
• Available mitigation strategies can deliver substantial emissions reductions, but additional options are needed to reach net zero. Limiting global warming to 2.7 degrees Fahrenheit above preindustrial levels requires a path to net-zero greenhouse gas emissions by 2050. Existing and planned fossil fuel infrastructure will produce emissions that will set the planet on a trajectory to exceed 2.7 degrees in the coming decades. Additional mitigation options need to be explored to reach net-zero emissions, and the United States will need to add new electricity-generating capacity, primarily wind and solar, faster than ever before.
• Climate action is an opportunity to create a more resilient and just nation. In addition to reducing risks to current and future generations, climate action can result in a range of immediate or near-term benefits that outweigh the costs, with the potential to improve well-being, strengthen resilience, benefit the economy, and, in part, redress legacies of racism and injustice.

“The Assessment is a stark reminder that, if we don’t act with urgency to tackle the climate crisis, Americans will experience increased suffering at the mercy of a changing environment,” says U.S. Secretary of Energy Jennifer M. Granholm in a DOE news release. “A bright spot in the sober assessment of where we are and where we could end up is the work we have been doing collectively as a country to reduce emissions and deploy alternative energy sources. I am proud of the DOE experts who contributed to this report and provided us with this eye-opening look at the existential threat of climate change and the opportunities to curb its worst impacts.”

A crucial part of the report, says Ullrich, is the NCA5 Atlas—a powerful and interactive tool that allows stakeholders, scientists, and the general public to examine the NCA5’s downscaled data. The data that fed the NCA5 Atlas was validated in a recently released DOE-funded report entitled Validation of LOCA2 and STAR-ESDM Statistically Downscaled Products. The analysis in this report provides evidence to support the use of this data by decision-makers.

Through the Office of Science and its National Laboratories, DOE contributed substantially to the scientific data NCA5 is based on by, for example, supporting the Energy Exascale Earth System Model simulation that reduced the uncertainty around future temperature estimates associated with the doubling of carbon dioxide. Climate observations conducted using DOE’s Atmospheric Radiation Measurement user facility—with locations in Alaska, Kansas, Oklahoma, and the Azores—strengthened and increased the accuracy of those simulations.

Contributing to NCA5 were the three DOE EESM program area managers and 20 DOE scientists, many of whom work on EESM projects. They included:  

• Xujing Davis, DOE EESM Earth System Model Development Program Manager
• Renu Joseph, DOE EESM RGMA Program Manager
• Robert Vallario, DOE EESM MultiSector Dynamics Program Manager
• Daniel Bilello, National Renewable Energy Laboratory
• Christa Brelsford, Oak Ridge National Laboratory
• Juan Pablo Carvallo, Lawrence Berkeley National Laboratory
• Rebecca Efroymson, Oak Ridge National Laboratory
• John Field, Oak Ridge National Laboratory
• Morgan Gorris, Los Alamos National Laboratory
• Forrest Hoffman, Oak Ridge National Laboratory
• Tianzhen Hong, Lawrence Berkeley National Laboratory
• David Judi, Pacific Northwest National Laboratory
• Zarrar Khan, Pacific Northwest National Laboratory
• Stephen Klein, Lawrence Livermore National Laboratory
• L. Ruby Leung, Pacific Northwest National Laboratory
• Ariel Miara, National Renewable Energy Laboratory
• David McCollum, Oak Ridge National Laboratory
• Claudia Tebaldi, Pacific Northwest National Laboratory
• Peter Thornton, Oak Ridge National Laboratory
• Paul Ullrich, Lawrence Livermore National Laboratory
• Nathalie Voisin, Pacific Northwest National Laboratory
• Michael Wehner, Lawrence Livermore National Laboratory
• Michael Westphal, Pacific Northwest National Laboratory

The USGRP is comprised of the U.S. Departments of Agriculture, Commerce, Energy, Health and Human Services, the Interior, and Transportation; the National Aeronautics and Space Administration; the National Science Foundation; and the Smithsonian Institution.