Shaping the Paris Agreement
CLIMATE CHANGE is one of the most pressing global issues. Rising temperatures and sea levels, and changing weather patterns that include heatwaves, droughts, and flooding, leave no part of the world untouched. It is an existential threat that requires international cooperation. One of the most significant moments in addressing climate change in this century was the Paris Agreement negotiation in 2015. That landmark international treaty was adopted at the U.N. Climate Change Conference (COP21) in Paris by nearly every country in the world to address climate change. Its central goal is to reduce greenhouse gas emissions enough to limit global warming to 2.0 degrees Celsius by the end of the century, and if possible 1.5 degrees. Exceeding that threshold risks more extreme climate events.
The Paris Agreement is unique in that it allows each country to set its own climate targets, known as Nationally Determined Contributions (NDCs), while committing to regular reporting, transparency, and increasing ambition over time. Rather than imposing top-down mandates, it creates a flexible framework that encourages global cooperation and accountability. Although the United States has now started to withdraw from the Paris Agreement for the second time under President Trump, the Paris Agreement remains one of the world’s largest and most significant international agreements.
The agreement is well known, but it’s not common knowledge that some of the ideas behind it were shaped at Harvard Kennedy School. Robert Stavins, director of the Harvard Project on Climate Agreements, founded in 2007, has conducted research and policy outreach that has helped shaped international conversations on climate, including those leading to the Paris Agreement.
In the years before the Paris Agreement, Stavins and collaborators explored the idea of “linkage”—connecting multiple greenhouse gas mitigation systems across countries or jurisdictions and allowing the trade of emissions units (or credits) between them. This can reduce overall costs and promote greater global ambition. In a departure from earlier efforts to link similar cap-and-trade systems, Stavins has focused on how to link diverse policy instruments—not only cap-and-trade systems, but also carbon taxes and other mechanisms. This work helped inform Article 6 of the Paris Agreement, which deals with international collaboration. In addition, the Harvard Project carried out research and outreach on a hybrid international climate agreement architecture that would combine top-down elements with bottom-up national pledges of action, which is exactly the structure that emerged with the Paris Agreement.
Joseph Aldy, who is the Teresa and John Heinz Professor of the Practice of Environmental Policy and previously served as codirector of the Harvard Project on Climate Agreements, has conducted diverse work with Stavins and others on how the international cooperation aspect of the Paris Agreement might work, and both Aldy and Stavins have consulted with and advised policymakers on climate agreements.
Aldy and coauthors conducted studies modeling the potential economic gains from cooperative implementation under Article 6, published in a 2021 paper. Their influential analysis estimated that linking NDCs via Article 6 could reduce global mitigation costs by about $300 billion a year by 2030, enabling up to 9 billion tons of additional CO₂ reductions annually.
Aldy, Stavins, and other HKS faculty continue to conduct insightful work on climate agreements, and representatives of the Project on Climate Agreements regularly attend climate conferences and convene meetings of policymakers and other experts on climate issues around the world.
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Alumni research in action
THE INTERGOVERNMENTAL PANEL on Climate Change (IPCC) is a key international body that assesses climate change science. Its assessments help inform COP decision-makers in their climate change negotiations. Laura Díaz Anadón MPP 2010 was a lead author on the 6th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) Working Group III on Climate Change Mitigation, published in 2022, and has been recently selected to serve as lead author in the ongoing 7th Assessment Report.
Díaz Anadón, who was also an assistant professor of public policy at HKS for three years, is now the chaired professor of climate change policy at the University of Cambridge. She is also a longtime affiliate of the Kennedy School’s Belfer Center and a former associate director of its Science, Technology, and Public Policy Program. In March 2022, she was selected as one of the 15 founding members of the European Scientific Advisory Board on Climate Change, where she has been twice elected vice-chair. This independent board, established by the European Climate Law of 2021, is charged with evaluating policies and identifying actions and opportunities with the goal of reaching climate neutrality by 2050.
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Banner image: Fareed Khan/AP Images; Christoph Soeder/AP Images; faculty portraits by Martha Stewart; courtesy of Laura Díaz Anadón