PNNL

Abstract

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. Scenarios were developed with input from policymakers, sector experts, and researchers. 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, 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.