India's Prime Minister Narendra Modi yesterday pledged to formally join the Paris climate change agreement this year, a potentially major step toward the pact entering into force.

After a meeting with President Barack Obama, a champion of the deal, in Vientiane, the White House said the two leaders had made a joint commitment "to join the Paris Agreement this year."

China and the United States, jointly responsible for about 38 percent of global emissions, ratified the Paris agreement on the eve of a meeting of G20 leaders meeting in Hangzhou, China, putting pressure on other major economies to follow suit.

The previous international effort to curb reliance on planet-harming fossil fuels, the Kyoto Protocol, had excluded China and other developing nations, while the United States refused to sign up.

The 180-nation deal sets ambitious goals for capping global warming and funnelling trillions of dollars to poor countries facing climate catastrophe.

It aims to limit global temperature increases to two degrees centigrade, and will be triggered after it is ratified by at least 55 countries, accounting for 55 percent of global greenhouse gas emissions.

India had been a reluctant adherent to the agreement, concerned that it would curb efforts to bring millions of Indians out of poverty.