There was the admiring essay about Modi that Obama wrote in Time magazine, and the image of them tete-a-tete at the Martin Luther King Jr Memorial in Washington, their entourages left behind. Obama's national security adviser said the two men had "chemistry," and expressed confidence that American interests made it "worth the investment in the relationship."

Exactly how much that investment has paid off will become clear this week during the climate negotiations on the outskirts of Paris, where India, the world's third-largest greenhouse gas polluter, has emerged as a pivotal player in shaping the outcome of a deal on which Obama hopes to build his legacy — or whether a deal emerges at all. So far, Indian negotiators have publicly staked out an uncompromising position.

India embodies a critical tension that will play out in Paris between developed nations like the United States, which are calling for universal emissions cuts, and developing nations like India, which say they deserve to increase fossil fuel use as their economies grow or else receive billions of dollars to transition to cleaner energy.

After Modi met Obama on Monday — their sixth meeting in 14 months — he told reporters that the two leaders had "such a deep relationship that we are able to openly discuss all issues," and said that he was happy to work "shoulder to shoulder with the United States."

But in an earlier speech on Monday, PM Modi said climate change was not India's fault, and blamed it firmly on "the prosperity and progress of an industrial age powered by fossil fuel."

"But we in India face its consequences today," he said.

That India has positioned itself as the champion of developing nations is no great surprise, based on past climate talks. But Modi, who wrote an e-book presenting the moral case for action on climate change, had been seen by US policymakers as a leader who might break that pattern.

"I think Obama got carried away with Modi, frankly," said Congress leader Jairam Ramesh, who served as minister of the environment under the previous government. Modi has made one major breakthrough in talks with Obama, Ramesh said, committing "against the advice of everyone in the system" to limit the use of hydrofluorocarbons, or HFCs, a component in refrigerators and air-conditioners. Since then, he said, India's negotiators have returned to their familiar, confrontational manner.

"India is not an easy country to negotiate with. We are moralistic, we are argumentative, we are regressive," Ramesh said. "It has gone back to the old rhetoric, there is no doubt about it."

India was the last major economy to submit its plans for a domestic climate change policy ahead of the Paris talks. And the proposal, while it included a significant expansion of renewable energy, would also see India's carbon pollution triple in the coming decades. Indian officials have painted that projection as a concession, saying that in a business-as-usual scenario, their emissions would soar at an even higher rate.