This week's climate pledges from the United States and China are aimed at cutting greenhouse gas emissions from the world's two largest sources. What about No. 3?

India—the world's third-biggest producer of carbon pollution—has not announced how it plans to help limit global warming. As part of ongoing United Nations-led climate treaty negotiations, however, every nation must offer something.

One thing is already obvious: India's offer probably won't resemble what the U.S. and China just announced. As an unidentified senior Indian negotiator told the Thethirdpole.net, "We cannot make the same commitment, or even a similar one. India and China are not in the same stage of development."

The United States on Tuesday agreed that in 10 years, it would reduce net greenhouse gas emissions to at least 26 percent below 2005 levels. China promised that its emissions of carbon dioxide would peak in the next 15 years, and that the share of non-fossil fuel energy consumption would rise to 20 percent by 2030. Together, the two countries produce about a third of global annual emissions of CO2, the primary culprit of global warming.

Many hailed the agreement as groundbreaking and an inspiration to other countries to make ambitious pledges in the coming months.

International climate talks resume next month in Lima, Peru, where nations will lay the groundwork for a global treaty to be signed during a December 2015 meeting in Paris. Countries are expected to announce emissions pledges by early next year.

India's Conundrum

India faces a tough balancing act in deciding what to promise on the climate front.

As the world's third-largest economy—and third-largest polluter—India's actions have an outsized impact on whether climate change can be sufficiently slowed. Yet expecting India to cut its total emissions isn't feasible—or fair—for a country still trying to raise the standard of living in areas without electricity or adequate roads and housing.

During climate talks in Copenhagen, rather than offering to scale back total emissions, India committed to a 20 to 25 percent reduction in its "carbon intensity" by 2020 compared to 2005. Carbon intensity is a useful gauge for fast-growing countries because it measures carbon dioxide emissions relative to economic growth, or per unit of gross domestic product.

India's new climate commitment could be an expansion of its earlier carbon-intensity pledge, according to Jake Schmidt, director of the Natural Resources Defense Council's international program. The country could also promise to step up its already aggressive push into renewable power.

"Prime Minister [Narendra] Modi has sent some pretty clear signals that they are going to double-down on wind and solar, and he has some very high targets," said Schmidt. "If he meets those, that would make a significant dent in slowing the growth of their greenhouse gas emissions, because they are mostly a coal-dependent economy."

On Path to No. 2 Polluter

The independent International Energy Agency, which released its annual World Energy Outlook report this week, put some stark numbers to the energy dilemma facing India and the world between now and 2040. The publication, among the most-cited energy reports in the world, projects how energy sources and trends might evolve under various scenarios.

The story of India, according to the IEA, is one of continuing economic growth and soaring energy use into the foreseeable future, while China's growth slows over the next 15 years and levels off around 2030.

Below is a look at how energy consumption and carbon emissions might play out in India, assuming the country doesn't make new proposals or enact new laws through 2040, and that carbon capturing technology doesn't make a meaningful difference. In short, the numbers paint a picture of a nation on track to eclipse the United States as the world's second-largest carbon polluter. The growth would occur well beyond the time when scientists say the world's total emissions have to be falling fast to keep global warming to 2 degrees Celsius.