The Kyoto Protocol, the world’s only internationally binding agreement to reduce greenhouse gas emissions, will expire in 2020. But the best chance for coming up with a replacement will come next year, in December 2015, when over 190 countries are scheduled to meet in Paris. Over the coming months, the world’s climate negotiators will scramble to meet this crucial deadline. And for the first time in decades, they have a good chance of succeeding, thanks to favorable political headwinds in the two countries that were once the biggest barriers standing in the way: Last week, Beijing and Washington announced a new agreement to reduce emissions in both countries. Under the joint plan, China will prevent its carbon emissions from growing after 2030 and the United States will reduce its emissions by 26 percent (from 2005 levels) by 2025. To the meet the new targets, China has said it will expand cap-and-trade programs to cover approximately ten percent of its economy. The United States, meanwhile, has announced plans to intensively regulate emissions from coal-fired power plants.

But now another holdout threatens to derail any attempt to produce a successor to Kyoto. India, as the world’s third-largest producer of greenhouse gases, has always been a crucial actor in international efforts to combat climate change. But now, with China finally ready to do something about greenhouse gases, New Delhi has become the single-biggest roadblock standing in the way. U.S. Secretary of State John Kerry acknowledged as much during a two-day trip to India in June 2013. “We have to recognize that a collective failure to meet our collective climate challenge would inhibit all countries’ dreams of growth and development,” he said. U.S. officials know that the road to a successful agreement in Paris runs through New Delhi; if climate negotiators want a truly global agreement, they must get India’s leadership on board.

The politics of climate change have long been defined by a divide between the developed and developing world, with the former emphasizing the shared nature of the challenge and the latter arguing that, since richer nations have done the most harm to the environment, they should make the most painful reductions. On many levels, it’s hard to argue with the developing countries’ position: The developed world has been responsible for most of the world’s human-caused greenhouse gas emissions over the past 250 years. But with the rapid economic growth of the past two decades, the annual contribution of large developing economies like China and India to global emissions has come to surpass that of many developed countries. In 2013, India’s carbon dioxide emissions increased by five percent, and they are expected to exceed those of the European Union by 2019. Unless every large economy, including India, agrees to limit and eventually reduce its emissions, efforts to cap global emissions will surely fail.

Two decades ago, disagreement between the developed and developing world led the U.S. Senate to refuse to ratify the Kyoto Protocol, creating a permanent deadlock in global climate negotiations. But in recent years, the tone has changed. As China has become the world’s leading producer of renewable energy, and pollution has become a major domestic issue there, Beijing has found the politics and economics of moving to a lower-carbon energy mix more favorable. The Chinese government has set up cap-and-trade systems in seven cities and provinces, with plans to expand, and it is in the process of setting a single price on carbon throughout the economy. More important for the climate negotiation process, Beijing has also signaled that it may be willing to cap national emissions as part of a new global deal. The European Union, which has always championed aggressive action on climate change, is set to reduce emissions by 40 percent below 1990 levels by 2040. Before the most recent agreement with China, the United States, for its part, had already pledged to reduce its own emissions by about 17 percent below 2005 levels, a figure to which it has now added nine percentage points.

Among the major greenhouse gas emitters, that leaves India. New Delhi has long maintained that it will not consider reductions while its emissions remain below the global average, even though they are rapidly increasing. Since India’s emissions were about 1.7 tons per person in 2013, compared with an average of about five tons globally, New Delhi won’t take aggressive action on climate change any time soon. Indeed, in September, India’s environment minister, Prakash Javadekar, suggested that the country would not consider cutting its emissions for at least another 30 years. Instead, Javadekar said, “India remains committed to pursuing a path of sustainable development through eradication of poverty, both of income as well as energy.”

Demand for energy in India is indeed surging, rising at a rate of about three percent annually. But one quarter of the country’s population—some 300 million people—lack basic access to electricity. In urban areas, blackouts and power outages are commonplace and a source of frequent complaints from the business community. Expanding access to energy, rather than reducing emissions, remains the overriding domestic political priority. And doing so will require greater reliance on fossil fuels; India is already the world’s third-largest producer of coal, which remains the country’s dominant energy source. Demand has increased at a rate of about seven percent annually since 2007.

Given this reality, it’s not surprising that India’s climate policy lacks clarity and ambition. In 2008, the Indian government released a “National Action Plan on Climate Change.” Although the plan included some important initiatives, such as a requirement that state utilities obtain a certain percentage of power from renewable sources, India’s overall emissions have since increased dramatically. And they are expected to grow by another 60 percent from 2020 to 2040—the period during which scientists say that global emissions will have to rapidly decline if climate change is to be halted.

Optimists point out that Narendra Modi, India’s current prime minister, expressed open concern about climate change when he was chief minister of the state of Gujarat and created a state department of climate change. But since taking office, the Modi government has sent mixed signals. In September, the prime minister made the bizarre assertion that “Climate change has not occurred. People have changed.” In the same month, Modi skipped the U.N. Climate Summit in New York, instead dispatching Javadekar, who said simply that emissions cuts “are for more developed countries.” Yet in other areas, Modi has played a more constructive role. During his visit to the United States this past October, Modi announced that India would phase out the use of hydrofluorocarbons (HFCs), synthetic compounds primarily used in refrigerants. The announcement was significant both because HFCs are a major contributor to climate change, and because India had previously opposed efforts to reduce the use of HFCs. It was also a notable achievement for U.S.–Indian cooperation, because the Barack Obama administration had announced a similar U.S. initiative several weeks earlier, enabling the administration to take credit for coordinated action. New Delhi has also promised to ramp up re-forestation programs and to significantly increase its solar power generation capacity.

Yet the world ultimately needs a bigger commitment from New Delhi to limit and significantly reduce its overall emissions. Without one, it will be difficult to reach a durable agreement in Paris next year and impossible to prevent dangerous climate change in the decades that follow. For Washington to have any chance of convincing India to make such a pledge, it needs to offer incentives in two crucial areas. First, Washington should do everything it can to move forward with the U.S.–Indian civil nuclear agreement, which allows India to purchase U.S. nuclear technology. The Indian government badly wants to increase its reliance on nuclear power so that it accounts for 25 percent of India’s energy by 2050, up from just three percent in 2011. Doing so would reduce India’s dependence on volatile and expensive imported fossil fuels and decrease the country’s greenhouse gas emissions—all while increasing energy production. Progress on the deal has stalled, though, with U.S. companies balking at Indian laws concerning liability for nuclear accidents. Washington should therefore redouble its efforts to encourage U.S. businesses and New Delhi to break the impasse; the resulting momentum would make New Delhi far more likely to adopt an ambitious stance in the Paris negotiations.

Second, Washington should expand partnerships with India’s subnational governments to bolster cooperation on climate change. India’s states have been far more aggressive in addressing the problem than New Delhi because they enjoy greater political freedom of action. The governments of Gujarat and Orissa, for example, have been working to expand production of renewable energy by offering generous subsidies. Moreover, Washington already has a successful model for this kind of cooperation with other countries: the U.S. government’s EcoPartnerships program, which pairs U.S. cities, states, universities and other entities with Chinese counterparts and supports joint initiatives focused on mitigating and adapting to climate change. The program has proved especially successful in China; so far, eight Chinese cities and provinces have signed agreements with their U.S. counterparts to tackle a variety of energy and climate policy challenges. Washington should build a similar program to engage Indian states under the auspices of the existing U.S.–India Green Partnership. To sweeten the deal, Washington could provide funding, on top of its regular aid, for adapting India’s infrastructure to better withstand the challenges climate change promises to bring, namely extreme weather events and rising water levels.

Climate politics have come a long way in a few short years. Most of the world’s developed countries have either implemented or announced significant cuts in their emissions, and China is poised to take similar steps. But that momentum will be lost unless India also pledges to limit and eventually cut its emissions. As the world’s climate negotiators travel the long road to Paris, they must keep their eyes on New Delhi. Washington, meanwhile, must focus on pushing the world’s largest democracy to play a greater role in tackling the world’s greatest environmental challenge.