The deal between China and the United States to limit greenhouse-gas (GHG) emissions, announced late on November 11 (U.S. time), is very significant—more because China and the United States are now cooperating so closely on climate change than because of the specifics of the deal. China is the largest and the United States the second largest emitter of GHGs, together accounting for approximately 36% of global emissions. The United States and China intend their pledges to become part of the major new multilateral agreement on climate change to be completed in Paris in late 2015. Given the example they have set, it is likely that their bilateral agreement will spur more ambitious mitigation contributions to the Paris agreement by other countries than would otherwise have been the case.
Having said that the fact of the China-U.S. collaboration is more important than the substance of the agreement, the pledges are impressive (though non-binding). The United States committed to reduce annual GHG emissions 26-28% by 2025, compared with 2005 levels. This represents a significantly accelerated pace of emissions reduction, compared with the United States’ previous commitment to a 17% reduction through 2020 over 2005. The latter pledge was made in the context of the Cancun Agreements, concluded at the Sixteenth Conference of the Parties (COP-16) of the United Nations Framework Convention on Climate Change (UNFCCC), in Cancun in December 2010 (building on the previous year’s COP in Copenhagen).
China committed to its CO2 emissions peaking no later than 2030 and to increasing the share of energy consumption from non-fossil-fuel (zero-emission) energy sources to 20%, also by 2030. China has never publicly committed to a peaking year before this time, though there were some semi-official murmurings earlier this year about the possibility, and China’s doing so now is a big deal.
China is already adding a great deal of non-fossil energy capacity (nuclear, renewables, hydro), which raises the question of how much the renewables pledge changes the business-as-usual trajectory. On the other hand, the share of non-fossil-fuel energy consumption in 2011 was only approximately 8%, and China is also rapidly adding fossil-fuel energy capacity, so it is likely that the mix of new capacity would need to change significantly to hit the 2030 peak. A recent MIT modeling study concurs, concluding that a peak during the period 2025-2035 (a scenario they label “accelerated effort,” as contrasted with scenarios with later peaks) would require “more aggressive measures,” which the authors describe in the report. So the renewables pledge is (probably) also a big deal.
As noted above, China and the United States offered their new climate pledges in the context of the upcoming Paris conference. Their bilateral agreement included explicit reference to language in the Durban Platform for Enhanced Action, adopted by COP-17 in late 2011, which, among other things, is the UNFCCC decision calling for the new 2015 agreement in the first place. Presidents Barack Obama and Xi Jinping:
“…reaffirmed the importance of strengthening bilateral cooperation on climate change and will work together, and with other countries, to adopt a protocol, another legal instrument or an agreed outcome with legal force under the Convention applicable to all Parties at the United Nations Climate Conference in Paris in 2015. They are committed to reaching an ambitious 2015 agreement that reflects the principle of common but differentiated responsibilities and respective capabilities, in light of different national circumstances.” [Text in italics approximately quotes the Durban Platform.]
The Durban Platform, “applicable to all Parties,” breaks sharply with the Kyoto Protocol, in which only developed countries had emissions-reduction commitments. All parties are required to make pledges as part of the 2015 agreement, and all pledges would have the same legal status (whatever that legal status ultimately turns out to be).
But developing countries have been concerned about equity: how will the principle of “common but differentiated responsibilities and respective capabilities” (CBDR, emphasis added), central to the Convention and to the equity concerns of developing countries, be realized in such an arrangement? The United States, other developed countries, and some developing countries (the last having had no commitments under Kyoto) have taken the position that CBDR would be satisfied by countries being free to make emissions-reduction pledges in whatever amount and in whatever form that their “different national [economic and political] circumstances” allowed. Differentiation, therefore, would be realized in the substance of the Paris pledges.
The bilateral agreement between China and the United States implicitly accepts this interpretation of the Durban Platform. The United States offers an economy-wide, quantified, absolute emissions-reduction target. China offers a peaking year, without specifying the emissions quantity at the peak or along either the upward or downward trajectories. China also offers a set of actions related to its energy mix. Thus, CBDR is satisfied through the varying types of pledges. There is no reference to legal form in the announcement, other than the language taken (approximately) from the Durban Platform itself. Implicitly, it appears, China and the United States accept the legal equivalency of their contributions under a future Paris agreement. This tacit concurrence between the two largest emitters effectively, if unofficially, relative to COP procedure, resolves the debate over how the Durban Platform should be interpreted and will surely smooth the path for other large-emitting countries to submit their pledges promptly and for the Paris agreement to be successfully concluded.
Some observers, including climate skeptics in the U.S. Congress and a few in the environmental community complain that China’s commitments under the bilateral agreement are too weak, incommensurate with the United States’, or both. Indeed, they are incommensurate—CBDR is part of the UNFCCC treaty to which both countries are party and allows for variations in the style and ambition of action, according to national circumstances (though, as noted, China’s commitments are environmentally significant).
Importantly, however, this deal helps lay an institutional foundation for effective climate action in the future—both the near future, with regard to the Paris agreement, and the longer-term future—which is important, as we’ll be dealing with climate change for a century or more. Such momentum could only come from a small group of the largest emitters acting in their national interest; it’s very difficult for the 195 countries in the UNFCCC to make dramatic leaps forward in the committee of the whole. A “minilateral” approach, embodied in the China-U.S. agreement, will catalyze action in the lead-up to Paris next year and increase the chances that the UNFCCC will produce a strong multilateral agreement.
 China: 22.3%; United States: 13.4%. In 2011, including land-use change and forestry, and all GHGs. World Resources Institute, Climate Analysis Indicator Tool (WRI CAIT), accessed November 13, 2014.
 For early examples of added pressure (that may or may not result in more ambitious 2015 climate pledges): Jairam Ramesh, “Big breakthrough in Beijing,” The Hindu, November 13, 2014; Ashley Hall, “US and China’s climate change agreement prompts calls for Australia to follow suit,” ABC (Australian Broadcasting Corporation), November 13, 2014.
 The fact sheet for the agreement states that “The new U.S. goal will double the pace of carbon pollution reduction from 1.2 percent per year on average during the 2005-2020 period to 2.3-2.8 percent per year on average between 2020 and 2025.”
 For a discussion of whether and how much China’s commitments represent deviations from business as usual, see Edward Wong, “China’s Climate Change Plan Raises Questions,” New York Times, November 12, 2014.
 Xiliang Zhang, et al., Carbon Emissions in China: How Far Can New Efforts Bend the Curve? MIT Joint Program on the Science and Policy of Global Change, October 2014. This report was referenced in the above cited New York Times article. Thanks to Joern Huenteler for separately bringing it to my attention. I admire the authors’ timing.
 UNFCCC, “Durban Platform for Enhanced Action,” December 10, 2011. The Durban Platform tasks the UNFCCC Parties to “…develop a protocol, another legal instrument or a legal outcome under the Convention applicable to all Parties…” See also Robert Stowe, “COP-19; Different Strokes,” The Energy Collective, November 27, 2013; Ottmar Edenhofer, Christian Flachsland, Robert Stavins, and Robert Stowe, Identifying Options for a New International Climate Regime Arising from the Durban Platform for Enhanced Action, Harvard Project on Climate Agreements and Mercator Research Institute on Global Commons and Climate Change, October 2013; Daniel Bodansky and Elliot Diringer. Building Flexibility and Ambition into a 2015 Climate Agreement, Center for Climate and Energy Solutions, June 2014.
 See here for the joint China-U.S. announcement. The joint announcement replaces “a legal outcome under the Convention” with “an agreed outcome with legal force under the Convention.” I will leave it to the international legal scholars to determine the significance of this substitution, but the language in the announcement is likely intentional.
 Robert Stavins, “The Platform Opens a Window: An Unambiguous Consequence of the Durban Climate Talks,” January 1, 2012.
 Jeremy Diamond, “Top congressional Republicans slam U.S.-China climate deal,” November 12, 2014.
 Almost all environmental groups have praised the deal.
 The European Union, collectively the third-largest emitter (9.3% of 2011 emissions; see WRI CAIT reference above), has already committed to a 40% reduction in GHG emissions below 1990 by 2030, as the first contribution to the 2015 Paris agreement. The EU, China, and the United States together account for approximately 45% of global GHG emissions. Ewa Krukowska, “EU Calls for 40% Reduction in Greenhouse-Gas Output by 2030,” Bloomberg, January 22, 2014. With regard to national interest: China has an interest in reducing conventional, local pollution from coal-fired power plants, which is causing significant health problems in Chinese cities. Even in undemocratic China, popular concern with local pollution is worrisome for the government. Energy security in China is also an important strategic objective, and China is seeking to reduce the need for imported oil over the long term. It is less clear how shorter-term U.S. national interest plays into the bilateral agreement, beyond a possible hope that accelerated energy-technology innovation will stimulate the economy in the short term (a misplaced hope, in my view). The Obama administration seems to be taking a long view on the threat of climate change.
 On “minilateralism,” see: Robyn Eckersley, “Moving Forward in the Climate Negotiations: Multilateralism or Minilateralism?” Global Environmental Politics 12 (2), 2012, pp. 24–42; Harvard Project on Climate Agreements, Institutions for International Climate Governance, November 22, 2010, esp. pp. 6-11; Sylvia I. Karlsson-Vinkhuyzen and Jeffrey McGee, “Legitimacy in an Era of Fragmentation: The Case of Global Climate Governance,” Global Environmental Politics 13 (3), 2013, pp. 56–78; Robert O. Keohane and David G. Victor, The Regime Complex for Climate Change, Harvard Project on Climate Agreements, January 2010, esp. pp. 6-7; Moisés Nairn, “Minilateralism,” Foreign Policy, no. 173, August 2009, pp. 135–36; Robert Stavins, Zou Ji, et al., “International Cooperation: Agreements and Instruments,” in Climate Change 2014: Mitigation of Climate Change: Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, O. Edenhofer, R. Pichs-Madruga, Y. Sokona, et al. (eds.), Cambridge University Press, 2014, esp. pp. 9, 23; Alexander Thompson and Daniel Verdier, Multi-Lateralisms: Explaining Variation in Regime Instruments, Harvard Project on Climate Agreements, March 2010, esp. p. 23.