International Relations Theory and the Paris Climate Agreement

Defensive realism vs. liberalism: explaining climate cooperation amidst great power rivalry

            Climate change is an existential threat to the planet. In the summer of 2021, one in three Americans experienced a climate disaster – whether from a heatwave, flash flood, wildfire, or drought[1]. Globally, more than 85% of the world’s population and four-fifths of the world’s landmass has suffered from extreme weather events linked to human-induced warming[2]. Tackling this problem requires significant, and rapid, international cooperation. The highlight of such cooperation to date has been the 2015 Paris Climate Agreement.

            Adopted by 195 countries on December 12th, 2015, the Paris Agreement marks the first truly global effort to rein in greenhouse gas (GHG) emissions, making it the most important international instrument in the fight against climate change. The primary goals of the agreement are to (1) “hold the increase in the global average temperature to well below 2°C above pre-industrial levels and limit the temperature increase to 1.5°C”, (2) “adapt to the adverse impacts of climate change and foster climate resilience”, and (3) make “finance flows consistent with a pathway towards low greenhouse gas emissions and climate-resilient development”.[3] Since the Paris Agreement came into force in November 2016, national policy, international business, and financial flows into technology and foreign investments are informed by these three goals. At the COP27 U.N. climate summit in Egypt last month, the key discussions primarily surrounded how nations are building upon their commitments in the Paris Agreement.[4]

How did the world arrive at such a landmark agreement? The history of climate negotiations has been littered with failures leading up to this moment, including the unwillingness of the U.S. to ratify the Kyoto Protocol in the early 2000s, and the collapse of the Copenhagen climate summit in 2009.[5] Nations have been uniquely reluctant to cooperate on climate change due to concerns of hindering their own economic development, perceived long time horizon to take action, free riders who incur benefits of other nations cutting emissions, and divides between developed and developing nations on who is obligated to do more/less.[6]  

The surprise success at Paris can be attributed to the two most powerful nations, and largest carbon dioxide emitters, coming together – the United States and China. Indeed, many analysts and insiders have argued Paris was only possible because of a bilateral agreement between the U.S. and China, without which no global, multilateral deal would have been able to go through.[7]  This makes the Paris Agreement an ideal setting to test competing theories of international relations that can explain the behavior of states. Though the two nations are locked in a great power rivalry, they were able to compromise on a global climate deal. Understanding how and why great power cooperation is possible in the realm of climate change can help inform the conditions of success for future climate negotiations and other transnational challenges. The two theories I will test are Kenneth Waltz’s defensive realism and G. John Ikenberry’s liberalism. I will outline each theory’s assumptions, causal logic, and observable implications to predict how and why the U.S. and China agreed to form the Paris Agreement and the kind of mechanism we should expect to see in the evidence if the theory is correct.

Waltz’s Defensive Realism: Theory and Observable Implications

            In Waltz’s defensive realist worldview, states are the main actors in a world whose current structure is that of anarchy. This anarchy encourages states to adopt moderate and restrained strategies in a quest to ensure their survival, not to maximize their own power. This is because attempts to maximize power would cause other states to be insecure and form counter-alliances against a rising threat.[8] Moreso, Waltz assumes that nation-states will always seek maintain their self-interests regardless of the consequences of their actions on other states. For this reason, realists are skeptical of inter-state cooperation because one state often seeks to gain more than the other. This is known as the issue of relative gains, making states wary of cooperation for fear that they will end up relatively weaker than those they are cooperating with.[9] Waltz, however, doesn’t see the challenge of relative gains hampering cooperation in all instances, arguing that states will likely cooperate when the gains are large, and a state faces an external security threat it cannot manage on its own.[10] For defensive realists, cooperation can also help manage the security dilemma – where an increase in one state’s security causes another state to perceive it as an aggressive act which decreases their security and answers in kind, causing a vicious spiral.[11] This security dilemma draws its roots in states being unsure of one another’s intentions, which can be resolved through increased cooperation and collaboration.

            Under a defensive realist lens, what could we expect to see in Chinese and American behavior leading up to and at the Paris Climate summit? As great powers, we could expect that both perceive climate change as a potential threat to their survival and as a result they are coming together out of a desire to maximize their survival, not their power. Statements or declarations framing climate change as a security threat will help confirm this. Given the scale of the challenge, they may also decide that they need to rise above their self-interests and fear of relative gains to counterbalance against the rising threat of climate change through cooperation. Evidence of this could be found in looking at the structure of the Paris Agreement to see if the United States or China allows one or the other to achieve relative gains in order for higher absolute gains through global collaboration. Lastly, to avoid a security dilemma they may engage in a number of consultations to better understand each other’s intentions and expectations leading up to the Paris summit. Here, I will look to see how frequently and to what extent the U.S. and China engaged in diplomatic talks to hash out specific positions before the summit.

Waltz’s Defensive Realism: Testing Hypotheses and Findings  

            First,China and America should both perceive climate change as a threat to their security prompting them to take action to maximize their chance of survival. Here, the evidence is overwhelming. At the 2015 State of the Union, President Obama declared that “No challenge poses a greater threat to future generations than climate change”[12]. A few months later in a speech to the U.S. Coast Guard, Obama went further, saying, “climate change constitutes a serious threat to global security, an immediate risk to our national security. And make no mistake, it will impact how our military defends our country.”[13]China framed the challenge in similarly dire ways. In a 900-page scientific assessment released in the weeks before the Paris Summit, China found that climate change will trigger international disputes within their borders due to conflicts over water resources and transnational migration. It even found that potentially every piece of infrastructure built on China’s coast is vulnerable.[14] China’s top weather scientist said climate change will have “huge impact” and China would emphasize “climate security.”[15]  

            Second, China and the U.S. should have sought to counterbalance against the rising, external threat of climate change through cooperation – conceding relative gains in the name of combatting a more formidable challenge that neither can solve alone. One example of this was the Paris Agreement stipulation that developed countries would contribute $100 billion annually to help vulnerable countries adapt and mitigate against climate change.[16] This decision, agreed to by the U.S., demonstrates a willingness by the U.S. concede financial gains in exchange for climate action. The strongest evidence, though, was China willing to give up, partially, the “common, but differentiated” responsibilities framework that had guided the last 20 years of climate negotiations. In 1995, the world gathered in Berlin to operationalize the United Nations Framework Convention on Climate Change (UNFCCC). Here, they arrived at the “Berlin Mandate” which declared that any emission cuts would primarily be borne by developed countries – like the U.S. and E.U. – excusing developing countries, like China, from any emission reduction targets.[17] In the years that followed, developing countries held strongly to this framework out of self-interest because they were highly suspicious of climate negotiations being used as a tool of developed countries to stymie their economic growth and development.[18]

Before the Paris Agreement, China still echoed its belief that “common, but differentiated responsibilities” should be the organizing principle of climate negotiations. Here, China was certainly acting in its own self-interests even though it had already become the world’s largest CO2 emitter by 2007. [19] However, China agreed to make emission cuts of its own for the first time in Paris – including peaking its CO2 emissions by 2030, increasing non-fossil fuels in its energy mix to 20%, reforesting 4.5 billion cubic meters of land, and lowering its CO2 emissions per unit of GDP by 60 to 65 percent.[20] This could reflect a decision calculus of defensive realism – China recognized the size and scope of an emerging threat and decided to forgo its self-interest of unhampered economic development, look past the relative gains that emission cuts would give its rivals, and collaborate with the developed countries to slow the impacts of climate change.

Third, China and the U.S. should have sought to limit the security dilemma by better understanding each other’s perspectives and intentions before Paris. There was ample evidence of the two nations carving out climate as a space to make common progress even while the two jostled for military and economic influence in the Indo-Pacific. For example, in 2013 the two established the U.S.-China Climate Change Working Group to cooperate on topics like energy efficiency, heavy industries, and sharing emissions data. [21] Xi and Obama both met two months before the Paris Summit hashing out a number of climate positions and declaring jointly that both nations would “strengthen bilateral coordination and cooperation…to promote sustainable development and the transition to green, low-carbon, and climate-resilient economies.”[22]

Ikenberry’s Liberalism: Theory and Observable Implications

            In opposition to defensive realism, G. John Ikenberry defines the world order not as an anarchic fight for survival and power, but as a set of “governing arrangements between states, including its fundamental rules, principles, and institutions” whereby institutional arrangements create a political process which ensures that various states in the order remain “linked and engaged with each other.”[23] Liberalism’s core beliefs are that the spread of democracy and economic interdependence through international institutions and arrangements will strengthen peace. Its theorists see a “slow but inexorable journey away from the anarchic world” as commerce and institutions bind nations together.[24] What are the characteristics of these institutions and the states that form them? Ikenberry argues that a leading state will want to create a constitutional settlement whereby they get weaker states to agree to be bound to a “set of rules and institutions” now and in the future. [25] In return, the leading power also offers to limit its own autonomy and arbitrary exercise of power. From the vantage point of the weaker states, they need assurances that the leading state will actually abide by its commitments and is credibly restrained, otherwise they will balance against them.[26]

            In order for both sides to maximally gain this assurance, Ikenberry suggests a “binding institutional settlement” that locks in countries within an institution. The highest form of this is when institutional agreements are formally ratified as treaties. Ikenberry argues that treaties contain the authority and force of legal agreements and embed them “in a wider legal and political framework that reinforces the likelihood that it will have some continuing force as state policy.”[27] Ikenberry goes on to suggest that leading states have more incentives to build the world order around binding institutions, and in particular democracies are better able and more willing to create them because of their openness and decentralization.[28]

            Under the lens of Ikenberry’s liberalism, the most significant observational implication we should expect is the United States as the leading state and China as the secondary state to come to Paris looking to create a binding institutional agreement to tackle climate change. I will look for evidence whereby the Paris Agreement was structured such that both countries would become locked into a set rules that endures beyond the existing power dynamic between the two of them, and where the United States gives up some freedom as the leading state in exchange for China coming on board. We should expect the United States as a democratic leading state to advocate for a treaty-based architecture with the force of legal authority to create a maximally “sticky” institution to shape and constrain state action from its rival well into the future.

Ikenberry’s Liberalism: Testing Hypotheses and Findings  

            In reality, U.S. did not come into Paris seeking to arrive at a binding international climate treaty structure. Instead, the U.S. advocated for a voluntary-based approach where countries would be able to set their own emission reduction goals, called Nationally Determined Contributions (NDC), which are submitted to the UNFCCC.[29] There is no legally binding mechanism to stick to those goals, instead reputational and peer pressure is exerted for countries to meet and “ratchet up” its targets over time.[30] The Paris Agreement itself has little legal enforcement as it does not impose any fees for penalties for violations of its terms and there is no governing body with authority to enforce compliance.[31] But as a creative workaround, negotiators made the need to issue an NDC as legally binding but did not impose a legal obligation to meet it. Some argue this hybrid structure is precisely why 195 countries joined.[32]

            The structure of the Paris Agreement hardly follows Ikenberry’s prescription, particularly for a leading state that is a democracy. In fact, the U.S. specifically advocated this structure because it would not require Congressional approval since the U.S. was not to be held legally accountable for any specific targets. The Paris Agreement’s voluntary structure seems to fail Ikenberry’s position that the U.S. would want to bind its nearest peer rival, China, into an agreement that would ensure its compliance and action in the future, rather focusing on limiting the constraints to its own self-interests while still advancing climate action.


            After examining the formation of the Paris Agreement through the lens of Kenneth Waltz’s defensive realism and G. John Ikenberry’s liberalism, I find that defensive realism has a stronger explanatory force for how the U.S. and China ultimately came to the table. Both recognized that climate change was a security threat to its position in the system and felt compelled to put aside their self-interest and fear of relative gains to balance against the threat. The scholarly implications are more damning for Ikenberry’s liberalism which could not explain why the U.S. did not seek to create a legally binding structure to credibly restrain either itself or China. In fact, I would argue that constructivism could better explain the treaty structure since meeting the Paris goals is based on peer pressure, values, and norms motivating climate action.[33]

The policy implications are that further climate action remains possible as long as the security threat remains, and the great powers in the system have a forum to collaborate and come to an understanding to take action. The era of binding international agreements for climate are seemingly over and liberalist approaches will not define the negotiations in the near-to-medium term. This is an avenue of future research to understand under what conditions the U.S. and China might be willing to explore binding commitments. A limitation of this research is that it only looks at publicly available documents whereas interviews with key negotiators could reveal what dimensions of the climate issue could be pressing enough to push the great powers into a legally binding architecture that enhances the durability of the Paris agreement.

Works Cited

[1] Sarah Kaplan and Andrew Ba Tran, “Nearly 1 in 3 Americans experienced a weather disaster this summer,” The Washington Post, September 4th, 2021,

[2] Annabelle Timsit and Sarah Kaplan, “At least 85 percent of the world’s population has been affected by human-induced climate change, new study shows,” The Washington Post, October 11th, 2021, 

[3] United Nations Framework Convention on Climate Change, “Adoption of the Paris Agreement,” December 12th, 2015,              

[4] Helen Briggs and Esme Stallard, “COP27: Why is the Paris climate agreement still important?”, BBC, November 2nd, 2022,

[5] Brad Plumer, “Past climate treaties failed. So the Paris deal will try something radically different.” Vox, Deceber 15th, 2015,

[6] Stefano Carattini, Simon Levin, and Alessandro Tavoni, “Cooperation in the Climate Commons”, Review of Environmental Economics and Policy, Volume 13, Number 2, Summer 2019,

[7] Robert Falkner, “A Minilateral Solution for Global Climate Change? On Bargaining Efficiency, Club Benefits, and International Legitimacy”, Cambridge University Press, March 21st, 2016, and Robert O. Keohane & David G. Victor, “Cooperation and discord in global climate policy”, Nature Climate Change volume 6, pages 570–575 (2016),

[8] Kenneth Waltz, “Theory of International Politics,” Addison-Wesley Publishing Company, 1979,

[9] Robert Powell, “Absolute and Relative Gains in International Relations Theory,” The American Political Science Review, Vol. 85, No. 4 (Dec., 1991), pp. 1303-132,

[10] Jeffrey W. Taliaferro, “Security seeking under anarchy: Defensive realism revisited” International Security, 25(3), 128–161, 2000-2001,

[11] Robert Jervis, “Realism, Neoliberalism, and Cooperation: Understanding the Debate,” International Security, Vol. 24, No. 1 (Summer, 1999), pp. 42-63,

[12] Madison Park, “Obama: No greater threat to future than climate change,” CNN, January 21st, 2015,

[13] President Barack Obama, “Remarks by the President at the United States Coast Guard Academy Commencement”, May 20th, 2015,

[14] Chris Buckley, “Chinese Report on Climate Change Depicts Somber Scenarios,” New York Times, November 29th, 2015,

[15] BBC, “Climate change: China official warns of ‘huge impact’”, March 22nd, 2015,

[16] NPR, “2 Degrees, $100 Billion: The World Climate Agreement, By The Numbers”, December 2nd, 2015,

[17] Bas Arts and Wolfgang Rudig, “Negotiating the ‘Berlin mandate’: Reflections on the first ‘conference of the parties’ to the UN framework convention on climate change”, Environmental Politics Volume 4, 1995 – Issue 3,

[18] Ibid. 17.

[19] John Vidal and David Adam, “China overtakes US as world’s biggest CO2 emitter,” The Guardian, June 19th, 2007,

[20] Center for Climate and Energy Solutions (C2ES), “CHINA’S CONTRIBUTION TO THE PARIS CLIMATE

AGREEMENT,” July 2015,

[21] U.S. Department of State, “U.S.-China Climate Change Working Group Fact Sheet”, July 10, 2013,

[22]  The White House, “U.S.-China Joint Presidential Statement on Climate Change,” September 25, 2015,

[23] G. John Ikenberry, “After Victory: Institutions, Strategic Restraint, and the Rebuilding of Order After Major Wars”, Princeton University Press, 2001.

[24] Jack Snyder, “One World, Rival Theories”, Foreign Policy, October 26th, 2009,

[25] Ibid. 23.

[26] Ibid. 23.

[27] Ibid. 23.

[28] Ibid. 23.

[29] Christopher Joyce, “Why Negotiators At Paris Climate Talks Are Tossing The Kyoto Model,” NPR, November 30th, 2015,

[30] United Nations, “The Paris Agreement,”,have%20joined%20the%20Paris%20Agreement

[31] Lila MacLellan, “Is the Paris Climate Agreement legally binding?”, Quartz, November 16th, 2021,

[32] Ibid. 31.

[33] John Boli and George Thomas, “Constructing World Culture: International Non-Governmental Organizations Since 1875, Stanford University Press, 1999,

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