After years of hiatus from international climate policy discussions, the U.S. reclaimed its seat at the table with the announcement of a net-zero greenhouse gas (GHG) emissions target by 2050. A comprehensive strategy towards this ambitious goal was then released at COP26 in Glasgow—the U.S. Long-Term Strategy (LTS)—details the decarbonization strategy with supporting analyses from integrated assessment modeling (IAM), individual sector modeling, and land modeling. These tools were previously used for quantitative research that supported the development of ambitious climate goals and now complete the circle by evaluating the policy they helped guide. In this Commentary, we describe the IAM modeling that underlies the quantitative analysis laid out in the U.S. LTS. We detail the lessons learned and highlight the value that collaborative scenario modeling can bring to developing robust Long-Term Strategies around the world.
The U.S. LTS was developed to describe how the United States can reach its newly announced national targets: 50-52% reductions from 2005 levels of greenhouse gas (GHG) emissions in 2030, and an economy-wide net-zero GHG emissions target no later than 2050. In the U.S. and other countries, commitments like these are important steps to prevent the worst consequences of climate change 2 , but reaching them will require a rapid and ambitious transformation of the energy system. Given this challenge, IAM modeling provides crucial support to anchor policy-making to scientific knowledge and ensure that plans are quantitatively coherent.
For the U.S. LTS, we complemented an economy-wide emissions cap to limit GHG emissions with sector-by-sector scenarios. To maximize the relevance of our modeling to the U.S. national context, these scenarios were developed through consultations with sector experts both inside and outside the government and by quantifying publicly announced sectoral targets, including 100% clean electricity by 2035 and 50% zero-emission light-duty vehicle sales by 2030. This scenario design results in an energy sector transformation pathway more consistent with current policy priorities, rather than a typical approach utilizing only an economy-wide carbon price.
The authors designed and executed the integrated assessment modeling for the United States long-term strategy. They bring diverse expertise to the modeling and analysis of United States decarbonization. Russell Horowitz, Matthew Binsted, and Haewon McJeon are scientists at the Joint Global Change Research Institute, a partnership between Pacific Northwest National Laboratory and the University of Maryland. Allen Fawcett, James McFarland, and Morgan Browning are economists at the Environmental Protection Agency’s Climate Economics Branch. Claire Henly is White House Fellow at the Office of the US Special Presidential Envoy for Climate. Nathan Hultman is the Director of the Center for Global Sustainability at the University of Maryland.