Fresh from a closed-door meeting with Chinese Vice Premier Zhang Gaoli, President Barack Obama called on other nations Tuesday to join the United States in confronting climate change, saying U.S. cuts to greenhouse gas pollution are bearing fruit but cannot accomplish the goal alone.

“Yes this is hard, but there should be no question that the United States of America is stepping up to the plate,” Obama said in a 14-minute address to the United Nations during a climate summit that saw world leaders pledge to take action while some developing nations’ representatives chided the West for doing too little. “We recognize our role in creating this problem. We embrace our responsibility to combat it. We will do our part, and we will help developing nations do theirs.”

World leaders need to stay focused on the climate threat and “look beyond the swarm of current events,” Obama added less than a day after the U.S. and its Arab allies launched military strikes on ISIL forces in Syria.

Obama singled out the “special responsibility to lead” that major greenhouse gas emitters such as the United States and China bear, even as he warned that no nation “gets a pass” on dealing with the problem. But the president also tacitly noted that China has surpassed the U.S. as the world’s top carbon polluter — saying he was in New York as “the leader of the world’s largest economy and its second-largest emitter to say we have begun to do something about it.”

And even rising nations that have yet to become major polluters in their own right will have to contribute to the solution, Obama told the crowd, saying that “nobody can stand on the sidelines on this issues.”

Obama mentioned that he had met a few minutes earlier with Zhang, who was attending the summit in lieu of Chinese President Xi Jinping. That meeting took place out of view of reporters accompanying Obama to New York.

Zhang spoke shortly after Obama, pledging that China will make “even greater efforts” to cut its carbon. But he maintained that “developed countries need to truly intensify emissions reductions and fulfill their obligations of providing financial support” to developing nations.

The last big international climate accord, adopted in 1997 in Kyoto, Japan, stirred the ire of opponents in Congress by exempting developing nations such as China and India. But advocates for developing nations have said it would be unfair to simply treat all countries the same, noting that industrialized countries like the U.S. had ample time to build their economies by burning fossil fuels.

Obama acknowledged that disparity but said the solution means “helping more nations skip past the dirty phase of development, using current technologies, not duplicating the same mistakes and environmental degradation that took place previously.”

As for the next big climate agreement, which is due next year in Paris, “We need an agreement that reflects economic realities in the next decade and beyond,” Obama said. “It must be ambitious — because that’s what the scale of this challenge demands. It must be inclusive — because every country must play its part. And yes, it must be flexible — because different nations have different circumstances.”

He was able to point to signs of progress in the U.S., including a sharp rise in investments in wind and solar power, dramatically tightened fuel-efficiency standards for cars and trucks, an overall decline in carbon pollution during the past eight years and his recently announced proposals to restrict greenhouse gas emissions from power plants. Unlike in many domestic speeches, Obama didn’t boast about the huge surge in U.S. oil and gas production that has taken place under his watch.

Obama also didn’t mention a major source of unhappiness for many U.S. climate activists — the continued uncertainty over whether he will approve the proposed Keystone XL oil pipeline from Canada.

Some climate activists welcomed the speech, though with the caveat that the U.S. still needs to do much more.

“President Obama’s speech today was encouraging, and the administration’s recent actions to curb emissions demonstrate leadership, but U.S. policy on the whole does not reflect the urgency of the president’s rhetoric,” Oxfam America President Raymond Offenheiser said in a statement. He added that “more substantial action by Congress and the president” are needed to meet the goal the U.S. and other countries set five years ago in Copenhagen for limiting global temperature rises to less-than-catastrophic levels.

Bill McKibben, the 350.org co-founder who organized Sunday’s massive climate march in New York City, said Obama needs to show “show a little more can-do spirit from the world’s leading economy.”

“Today’s boasts about his climate efforts ring hollow in the face of America passing Saudi Arabia and Russia as the world’s largest oil and gas producer,” McKibben said. “We hope that when ‘next year’ comes and he proposes actual targets they’ll start to reverse the trend.”

Obama appeared to acknowledge Sunday’s march as he touted his administration’s work on a panoply of internal and multilateral efforts, including a pact to curb methane emissions from natural gas drilling operations that became public earlier Tuesday.

“None of this is without controversy,” Obama told the gathered heads of state and diplomats. “In each of our countries, there will be interests that are resistant to action.”

The speech came as the White House announced a series of measures to boost global resilience to the effects of climate change, including an executive order signed Tuesday, and the U.S. and other nations announced initiatives to address pieces of the problem through efforts like sustainable agriculture.