Harvard Project on Climate Agreements Archives - An Economic View of the Environment

What to Expect at COP-28 in Dubai

With just a few days remaining until the start of the 28^th Conference of the Parties (COP28) of the United Nations Framework Convention on Climate Change (UNFCCC) in Dubai, United Arab Emirates (UAE), COP28 is the focus of this blog post and my most recent podcast. In the podcast, I engage in conversation with environmental economist Nathaniel Keohane, the president of the Center for Climate and Energy Solutions (C2ES). Nat will be leading the C2ES delegation at COP28. I’ll also be at COP28, with our group from the Harvard Project on Climate Agreements. So, at the end of this blog post, I provide a list of Harvard activities at COP28.

This is a special pre-COP episode of “Environmental Insights: Discussions on Policy and Practice from the Harvard Environmental Economics Program,” which is produced by the Harvard Environmental Economics Program. Listen to the conversation here.

Keohane, before becoming president of C2ES, was Senior Vice President for Climate at the Environmental Defense Fund (EDF), and before that served in the Obama Administration as Special Assistant to the President for Energy and Environment.

In our podcast conversation, Nat explains that the “Global Stocktake” will play a prominent role at COP28 in Dubai beginning later this week. In fact, he expresses considerable optimism that the Global Stocktake will provide incentives for participating nations to step up their collective efforts to slow the rise of global temperatures.

“What we’re looking for coming out of this COP is to highlight a handful of those high-level political signals coming out of this global stocktake. Things like a commitment to triple renewable energy globally by 2030. Things like slashing methane emissions. You can imagine a handful of others on land use and carbon sinks, on adaptation and global finance, a handful of things that can define an action agenda for 2024 and then can inform what countries do when they set those more ambitious targets in 2025. That’s the real centerpiece of this COP,” he says. “The goal is to catalyze action and collaborative cooperative action in 2024, looking ahead to 2025, not just simply to say, ‘Well, gee, we’re off track. That’s too bad’… We need to catalyze action going forward.”

Keohane remarks that the controversial issue of “Loss and Damage” will also play a prominent role in the negotiations this year as the concept of providing financial support to the nations hardest hit by climate change becomes more widely accepted.

“I think we’ve come a long way with the recognition that there are damages that the most vulnerable countries are going to suffer, are suffering already, that go beyond simply the investments in adaptation and climate resilience, and that there needs to be some way to address those. And I think we’ve made a fair amount of progress, even though it’s not going to be satisfying to everybody right away,” he says. “I think it’s the first step towards an institution over time that can grow and build and become something more important.”

We discuss how the recent COPs have grown larger with a growing contingency of participants from the private sector, NGOs, and multi-lateral organizations that are dedicated to advancing the goals of the Paris Agreement.

“[The COP] really becomes a magnet, a draw for everybody working on climate. And the fact that all those side events have become so big I think reflects the fact that climate is now central to the decisions that policymakers are making, not just in a Climate Ministry or an Environment Ministry, but in the Treasury and in Finance Ministries and in Energy Ministries and so on. Climate is [also] central to what businesses are doing and how they’re making plans,” Nat says. “I’ve always been of the view [that if] we didn’t have the COP already we would have to invent it because we need that kind of focal point for people to come and gather talking about what I think is the most existential issue of our time.”

For this and much more, I encourage you to listen to our complete conversation in this 54^th episode of the Environmental Insights podcast series.

As I noted at the outset of this blog post, both Keohane and I will participate in COP28 events in Dubai. So I close this special pre-COP edition of my blog with a description of some of our own – that is, Harvard – activities at COP28.

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Linked with my current role as director of a Harvard-wide initiative on Reducing Global Methane Emissions, which I’ve described in detail in previous essays at this blog, much – but not all – of our focus at COP28 will be on methane and related public policies. Indeed, efforts around and impacts of global methane-emissions abatement will be our focus in our official Side Event on December 6, at COP28.

Reducing Global Methane Emissions: Imperatives, Opportunities, and Challenges

This panel will feature several leading scholars and climate policy experts who will discuss current research and practice on technology, policy, and international cooperation, drawing in part on Harvard’s major new methane initiative supported by the Salata Institute for Climate and Sustainability at Harvard University. I will moderate the discussion.

The other panelists will be:

Stephen Hammer, Chief Executive Officer, New York Climate Exchange, and former Methane Lead, World Bank;
Claire Henly, Senior Advisor for Non- CO2 greenhouse gases, US Special Presidential Envoy for Climate;
Daniel Jacob, Vasco McCoy Family Professor of Atmospheric Chemistry and Environmental Engineering, Harvard University and global expert on satellite-based methane detection and attribution;
Helena Varkkey, Associate Professor of Environmental Politics and Governance, Universiti Malaya and Principal Investigator, UM-CERAH-EDF initiative on methane emissions in Malaysia

Time, Date, and Location: December 6, 2023, 3:00 – 4:30 pm local time, Side Event Room 4, COP-28, Expo City, Dubai

(Note: All official side events are within the “Blue Zone” at COP-28; registration for the COP and a badge are required to enter)

For questions and further information about this and the other COP28 events that follow below, please contact: Jason Chapman (Jason_chapman@hks.harvard.edu).

Some other speaking engagements of mine at COP28 include:

Net Zero in Action: Showcasing Decarbonization Technologies

December 5, 10:00 – 11:30 am, panelist at IPIECA event: “Net Zero in Action: Showcasing Decarbonization Technologies,” Pavilion of the International Emissions Trading Association, Blue Zone.

Transforming High Global Warming Potential Sectors through Carbon Markets

December 6, 9:00-10:30 am, panelist, where RNS will make a presentation on “The Promise and Peril of GHG Markets for Reducing Global Methane Emissions,” Asian Development Bank Pavilion, Blue Zone

Application of Low Emission Development Strategies and Progress of Global Energy Transition

December 6, 1 – 2:30 pm, Robert Stavins is a panelist at Ninth Global Climate Change Think Tank Forum. The event is hosted by China’s National Center for Climate Change Strategy and International Cooperation. Theme: “Application of Low Emission Development Strategies and Progress of Global Energy Transition,” China Pavilion, Blue Zone.

In addition to Professors Stavins and Jacob, the Harvard delegation in Dubai will include several leading scholars from the Harvard T.H. Chan School of Public Health (HSPH) and others from around Harvard.

HSPH is sponsoring two events at COP-28:

“Linking Agendas of the UNFCCC and the World Health Assembly – Regional perspective,” 3 – 4:30 pm, December 6, Guatemala Pavilion, Blue Zone.

“Linking Agendas of the UNFCCC and the World Health Assembly – Global perspective,” 9:30 – 10:45 am, December 12, WHO Pavilion, Blue Zone.

For more information on the HSPH events, contact Liz Willetts (ewilletts@hsph.harvard.edu).

I hope to see many of you at one or more of these events, and/or other meetings, in the hallways, or elsewhere at COP28 in Dubai!

Finally, I want to remind you to listen to this 54^th episode of the Environmental Insights series, with future episodes scheduled to drop each month. You can find a transcript of our conversation at the website of the Harvard Environmental Economics Program. Previous episodes have featured conversations with:

Gina McCarthy, former Administrator of the U.S. Environmental Protection Agency
Nick Stern of the London School of Economics discussing his career, British politics, and efforts to combat climate change
Andrei Marcu, founder and executive director of the European Roundtable on Climate Change and Sustainable Transition
Paul Watkinson, Chair of the Subsidiary Body for Scientific and Technological Advice (SBSTA) within the United Nations Framework Convention on Climate Change
Jos Delbeke, professor at the European University Institute in Florence and at the KU Leuven in Belgium, and formerly Director-General of the European Commission’s DG Climate Action
David Keith, professor at Harvard and a leading authority on geoengineering
Joe Aldy, professor of the practice of public policy at Harvard Kennedy School, with considerable experience working on climate change policy issues in the U.S. government
Scott Barrett, professor of natural resource economics at Columbia University, and an authority on infectious disease policy
Rebecca Henderson, John and Natty McArthur University Professor at Harvard University, and founding co-director of the Business and Environment Initiative at Harvard Business School.
Sue Biniaz, who was the lead climate lawyer and a lead climate negotiator for the United States from 1989 until early 2017.
Richard Schmalensee, the Howard W. Johnson Professor of Management, and Professor of Economics Emeritus at the Massachusetts Institute of Technology.
Kelley Kizier, Associate Vice President for International Climate at the Environmental Defense Fund.
David Hone, Chief Climate Change Adviser, Shell International.
Vicky Bailey, 30 years of experience in corporate and government positions in the energy sector.
David Victor, professor of international relations at the University of California, San Diego.
Lisa Friedman, reporter on the climate desk at the The New York Times.
Coral Davenport, who covers energy and environmental policy for The New York Times from Washington.
Spencer Dale, BP Group Chief Economist.
Richard Revesz, professor at the NYU School of Law.
Daniel Esty, Hillhouse Professor of Environment and Law at Yale University.
William Hogan, Raymond Plank Research Professor of Global Energy Policy at Harvard.
Jody Freeman, Archibald Cox Professor of Law at Harvard Law School.
John Graham, Dean Emeritus, Paul O’Neill School of Public and Environmental Affairs, Indiana University.
Gernot Wagner, Clinical Associate Professor at New York University.
John Holdren, Research Professor, Harvard Kennedy School.
Larry Goulder, Shuzo Nishihara Professor of Environmental and Resource Economics, Stanford University.
Suzi Kerr, Chief Economist, Environmental Defense Fund.
Sheila Olmstead, Professor of Public Affairs, LBJ School of Public Affairs, University of Texas, Austin.
Robert Pindyck, Bank of Tokyo-Mitsubishi Professor of Economics and Finance, MIT Sloan School of Management.
Gilbert Metcalf, Professor of Economics, Tufts University.
Navroz Dubash, Professor, Centre for Policy Research, New Delhi.
Paul Joskow, Elizabeth and James Killian Professor of Economics emeritus, MIT.
Maureen Cropper, Distinguished University Professor, University of Maryland.
Orley Ashenfelter, the Joseph Douglas Green 1895 Professor of Economics, Princeton University.
Jonathan Wiener, the William and Thomas Perkins Professor of Law, Duke Law School.
Lori Bennear, the Juli Plant Grainger Associate Professor of Energy Economics and Policy, Nicholas School of the Environment, Duke University.
Daniel Yergin, founder of Cambridge Energy Research Associates, and now Vice Chair of S&P Global.
Jeffrey Holmstead, who leads the Environmental Strategies Group at Bracewell in Washington, DC.
Daniel Jacob, Vasco McCoy Family Professor of Atmospheric Chemistry & Environmental Engineering at Harvard.
Michael Greenstone, Milton Friedman Distinguished Service Professor of Economics, University of Chicago.
Billy Pizer, Vice President for Research & Policy Engagement, Resources for the Future.
Daniel Bodansky, Regents’ Professor, Sandra Day O’Connor College of Law, Arizona State University.
Catherine Wolfram, Cora Jane Flood Professor of Business Administration, Haas School of Business, University of California, Berkeley, currently on leave at the Harvard Kennedy School.
James Stock, Harold Hitchings Burbank Professor of Political Economy, Harvard University.
Mary Nichols, long-time leader in California, U.S., and international climate change policy.
Geoffrey Heal, Donald Waite III Professor of Social Enterprise, Columbia Business School.
Kathleen Segerson, Board of Trustees Distinguished Professor of Economics, University of Connecticut.
Meredith Fowlie, Professor of Agricultural and Resource Economics, U.C. Berkeley.
Karen Palmer, Senior Fellow, Resources for the Future.
Severin Borenstein, Professor of the Graduate School, Haas School of Business, University of California, Berkeley.
Michael Toffel, Senator John Heinz Professor of Environmental Management and Professor of Business Administration, Harvard Business School.
Emma Rothschild, Jeremy and Jane Knowles Professor of History, Harvard University.

“Environmental Insights” is hosted on SoundCloud, and is also available on iTunes, Pocket Casts, Spotify, and Stitcher.

Reflections on Economics and Policy Making in the Environmental Domain

This past week, I was privileged to participate in a workshop, “Climate Science in a Time of Political Disruption,” sponsored by the Harvard Program on Science, Technology and Society. The workshop began with a keynote address by former U.S. Environmental Protection Agency Administrator Gina McCarthy, now Professor of Practice at the Harvard T. H. Chan School of Public Health. Following Gina McCarthy’s down-to-earth but quite inspiring remarks (with her usual Yankee humor adding spice to the proceedings), the others on the panel were asked to comment on the topic at hand. The panelists included Joe Goffman, Executive Director of the Environmental Law Program at Harvard Law School; Peter Huybers, Professor of Earth and Planetary Sciences; Sheila Jasanoff, Pforzheimer Professor of Science and Technology Studies at the Harvard Kennedy School; Lucas Stanczyk, Assistant Professor of Philosophy; and myself.

Given the subject of the workshop, most of the panelists focused their comments on the current political scene and the current U.S. administration’s apparent disdain for climate science. I took a broader, somewhat historical view, and as the only economist on the panel, I commented on the relationship of economic research to policy making. I did this via reflections on experiences I’ve had over the past three decades. I tried to make three points: first, economic research results can be used as a light bulb or a rock, and either can be effective; second, it is important to move quickly when windows of opportunity open in the policy world to implement research ideas; and third, politics matter, and should not be ignored.

Research Results Can be Used as a Light Bulb or a Rock

I cannot speak for the natural sciences, but it is clearly the case that economic evidence can be used either as a “light bulb” – to illuminate an issue and possibly persuade policy makers of the wisdom of a particular course of action – or as a “rock,” that is, as ammunition to support a policy maker’s predisposed position. Is this cynical? I think not, because such economic ammunition can help win a policy battle. I was just reminded by Paul Krugman in his New York Times column of a somewhat less charitable metaphor, where he characterized some politicians as using economists “the way a drunkard uses a lamppost: for support, not illumination.”

Related to this reality was a session I chaired in 2001 at the annual meetings of the American Economic Association – a roundtable of former chairs and members of the U.S. Council of Economic Advisers (CEA), including George Eads (Charles River Associates), the late William Niskanen (then of the Cato Institute), William Nordhaus (Yale University), and Joseph Stiglitz (Columbia University). A repeated theme from this set of economists was the reality that CEA typically had more influence by helping others in the Executive Office of the President in their efforts to stop bad ideas than by itself promoting good ideas.

When Windows of Opportunity Open, Move Quickly

Two examples stand out for me of the importance of moving quickly when windows of opportunity open in the policy world to implement research ideas. One is the work I carried out in the late 1980s under the sponsorship of the late Republican Senator John Heinz of Pennsylvania and former Democratic Senator Timothy Wirth of Colorado in the form of research that led to a report, “Project 88: Harnessing Market Forces to Protect the Environment.” One of the proposals in the report was to address the then politically prominent problem of acid rain with what is now called a cap-and-trade system. This idea resonated with the incoming administration of President George H. W. Bush, particularly with the Counsel to the President, Boyden Gray. In parallel with work being carried out by Joe Goffman and Dan Dudek (both then at the Environmental Defense Fund), I followed up the Project 88 report with numerous White House and other Washington meetings (commuting weekly from my Harvard perch), which eventually contributed to the Bush Administration’s proposal (to an initially resistant Democratic Congress) of the Clean Air Act Amendments of 1990, including its path-breaking sulfur dioxide allowance trading program.

The other example I mentioned to highlight the importance of moving quickly when windows of opportunity open in the policy world is associated with the negotiations carried out annually under the United Nations Framework Convention on Climate Change (UNFCCC). At the seventeenth Conference of the Parties of the UNFCCC in Durban, South Africa, in 2011, the delegates agreed to the “Durban Platform for Enhanced Action,” which broke with nearly twenty years of UNFCCC policy by mandating a new approach in which all countries, not just the richest nations, would participate in addressing the need for greenhouse gas (GHG) emissions reductions. The key challenge for climate negotiators was how to meet this new mandate while still observing the fundamental UNFCCC principle of “common but differentiated responsibilities,” which had previously been interpreted to mean that rich countries alone would shoulder the burden of reducing emissions.

At the Harvard Project on Climate Agreements, we recognized that negotiators around the world were suddenly open to outside-the-box thinking. Indeed, in Science magazine, my colleague, Joe Aldy, and I wrote an article, “Climate Negotiators Create an Opportunity for Scholars.” Over the following months (and years) we worked hard to help key negotiating countries develop a new policy architecture that could meet the challenge before them. The result was a hybrid approach that combined elements of top-down architecture with a healthy dose of bottom-up “pledge-and-review,” which led eventually, of course, to the Paris Agreement of 2015.

Politics Matter

For the Intergovernmental Panel on Climate Change’s (IPCC) Fifth Assessment Report (AR5), I served as Coordinating Lead Author (with Dr. Zou Ji of China) of the chapter on “International Cooperation: Agreements and Instruments.” I was surprised to find that the process was highly politicized – in two distinct ways. First, whereas I had assumed that the Lead Authors (LAs) serving on our writing team were there only to represent their respective scientific expertise (in economics, legal scholarship, international relations, etc.), some of the LAs seemed to represent the interests of their respective countries.

Second, I was very naive about the final step of the process, when the governments of the world are asked to approve the IPCC’s Summary for Policy Makers line by line. The controversy associated with our chapter on international climate agreements resulted in that entire section of the SPM being eviscerated of all meaningful substance at the Government Approval Sessions for Working Group III (WG III) in Berlin in April, 2014. I was disappointed and dismayed by the process and its outcome.

Fortunately, I learned from that experience and my attitude (and behavior) was quite different just six months later, when I found myself in Copenhagen for what was essentially the final stage of the entire five-year enterprise of research, writing, and government approval of the various reports of IPCC AR5, namely the government approval sessions for the Synthesis Report (SYR), which summarizes and synthesizes the key findings from all three Working Group reports. I had learned my lesson. Rather than disdaining the politics of the occasion, I embraced it and spent the week in Copenhagen in careful negotiations with the key national governments, the result of which was that all of the essential text on international cooperation and agreements was preserved in the Synthesis Report.

Ironically, by recognizing, accepting, and indeed participating in the fundamentally political aspects of the IPCC government approval process, I was able to keep the report of research from itself being politicized.

Summing Up

So, the three points I made regarding the relationship between economic research and policy making at last week’s Harvard workshop were these: first, economic research results can be used as a light bulb or a rock, and either or both can be effective; second, it is important to move quickly when windows of opportunity open in the policy world to implement research ideas; and third, politics matter, and should not be ignored.

I left it to others at the workshop – and I leave it to readers of this essay – to judge whether any of this applies more broadly to “Climate Science in a Time of Political Disruption.”

Market Mechanisms in the Paris Climate Agreement: International Linkage under Article 6.2

The Harvard Project on Climate Agreements hosted a research workshop in Cambridge, Massachusetts, on July 14–15, 2016, the purpose of which was to identify options for elaborating and implementing the Paris Climate Agreement, and to identify policies and institutions that might complement or supplement the United Nations Framework Convention on Climate Change (UNFCCC) process. We were motivated by our recognition that while the Paris Agreement sets forth an innovative and potentially effective policy architecture for dealing with global climate change, a great deal remains to be done to elaborate the accord, formulate required rules and guidelines, and specify means of implementation.

Participants in the workshop – International Climate Change Policy after Paris – included twenty-one of the world’s leading researchers focusing on climate-change policy, representing the disciplines of economics, political science, international relations, and legal scholarship. They came from Argentina, Belgium, China, Germany, India, Italy, Norway, the United Kingdom, and the United States. (A list of workshop participants is here, biographies here, and the agenda here.)

The Harvard Project will next focus on communicating the ideas, insights, and recommendations of workshop participants to climate negotiators and policy makers, in the expectation that they might prove useful in elaborating and implementing the Paris Agreement. Each participant is preparing a brief—based largely on her or his presentation during the workshop. These briefs, together with a workshop summary, will be conveyed to participants in the Twenty-Second Conference of the Parties (COP-22) of the UNFCCC in Marrakech, Morocco in November 2016. This will be done in meetings with negotiators representing UNFCCC member governments and in a side-event panel at COP-22.

Today I wish to share with readers just one of these draft briefs – namely, my own – on the topic of “International Linkage under Article 6.2 of the Paris Agreement.”

A Key Challenge for Sustained Success of the Paris Agreement

For sustained success of the international climate regime, a key question is whether the Paris Agreement with its Intended Nationally Determined Contributions (INDCs), anchored as they are in domestic political realities, can progressively lead to submissions with sufficient ambition? Are there ways to enable and facilitate increased ambition over time?

Linkage of regional, national, and sub-national policies can be part of the answer. By “linkage,” I mean connections among policy systems that allow for emission reduction efforts to be redistributed across systems. Such linkage is typically framed as being between two (or more) cap-and-trade systems, but national policies will surely be highly heterogeneous under the Paris climate regime. Fortunately, research – by Gilbert Metcalf of Tufts University and David Weisbach of the University of Chicago – indicates that linkage between pairings of various types of domestic policy instruments may be feasible.

Linkage and the Paris Agreement

Experience indicates that linkage will bring both merits and concerns in most applications. To begin with the good news, linkage offers a number of important advantages. First, it offers the possibility of achieving cost savings if marginal abatement costs are heterogeneous across jurisdictions, which they surely are. In addition, linkage can improve the functioning of individual markets by reducing market power, and by reducing price volatility, although we should recognize that price volatility will also be transmitted from one jurisdiction to another by linkage. Finally linkage can allow for the UNFCCC’s important principle of Common but Differentiated Responsibilities (CBDR), but do so without sacrificing cost-effectiveness.

The possibility of linkage also raises concerns, including that there will be distributional impacts within jurisdictions, that is, the creation of both winners and losers. Also, linkage can bring about the automatic propagation from one jurisdiction to another of some design elements, in particular, cost-containment mechanisms, such as banking, borrowing, and price collars. In this and other ways, linkage raises concerns about decreased autonomy.

Linkage under Article 6.2 of the Paris Agreement

It was by no means preordained that the Paris Agreement would allow, let alone encourage, international linkage. Fortunately, the negotiations which took place in Paris in December, 2015, produced an Agreement that includes in its Article 6.2 the necessary building blocks for linkages to occur.

Under Article 6.2, emissions reductions occurring outside of the geographic jurisdiction of a Party to the Agreement can be counted toward achieving that Party’s Nationally Determined Contribution (NDC) via Internationally Transferred Mitigation Outcomes (ITMOs). This enables both the formation of “clubs” or other types of coalitions, as well as bottom-up heterogeneous linkage. Such linkage among Parties to the Agreement would provide for exchanges between compliance entities within the jurisdictions of two different Parties, not simply the government-to-government trading (of Assigned Amounts or AAUs), as was the case with the Kyoto Protocol’s Article 17.

Linkage among Heterogeneous Nationally Determined Contributions

There are three types of heterogeneity which are important in regard to linkage under Article 6.2 of the Paris Agreement. First is heterogeneity among policy instruments. As demonstrated by Metcalf and Weisbach (see above), not only can one cap-and-trade system be linked with another cap-and-trade system, but it is also possible to link a cap-and-trade system with a carbon tax system. In addition, either a cap-and-trade system or a tax system can be linked (via appropriate offsets) with a performance standard in another jurisdiction. (Linkage with systems employing technology standards are not feasible, however, because such systems are not output-based.)

A second form of heterogeneity that affects linkage and is potentially very important under the Paris Agreement is heterogeneity regarding the level of government action of the relevant jurisdictions. Although the Paris Agreement has as Parties both regional jurisdictions (in the case of the European Union) and national jurisdictions, sub-national jurisdictions are also taking action in some parts of the world. In fact, linkage has already been established between the state of California in the United States and the provinces of Québec and Ontario in Canada.

A third form of relevant heterogeneity is with regards to the NDC targets themselves. Some are in the form of hard (mass–based) emissions caps, while others are in the form of rate-based emissions caps, either emissions per unit of economic activity, or emissions per unit of output (such as per unit of electricity production). There are also relative mass-based emissions caps in the set of existing NDCs, such as those that are relative to business-as-usual emissions in a specific future year. Beyond these, there are other parties that have put forward NDCs that do not involve emission caps at all, but rather targets in terms of some other metric, such as the degree of penetration of renewable energy sources.

Combinations of various options under these three forms of heterogeneity yield a considerable variety of types of potential linkages, which may be thought of as the cells of a three-dimensional matrix. Not all of these cells, however, represent linkages which are feasible, let alone desirable.

The Path Ahead – Key Issues and Questions

There are a substantial number of issues that negotiators will eventually need to address, and likewise, there are a set of questions that researchers (including within the Harvard Project on Climate Agreements) can begin to address now. Among the key issues for negotiators will be the necessity to develop accounting procedures and mechanisms. Also, it will be important to identify means for the ITMOs to be tracked in order to avoid double-counting of emissions reductions. And a broader question is whether and how the UNFCCC Secretariat or some other designated institution will provide any oversight that may be required.

For research, three questions stand out. First, among pairings from the (3-D matrix) set of instrument–jurisdiction–target combinations that emerge from the three types of heterogeneity identified above, which linkages will actually be feasible? Second, within this feasible set, are some types of linkages feasible, but not desirable? And third, what accounting treatments and tracking mechanisms will be necessary for these various types of linkages? Future research will need to focus on these and related questions in order to achieve the potential benefits of Article 6.2 of the Paris Agreement. Please stay tuned as this work develops.