U.S. President Barack Obama says inaction on climate change could leave future generations with an "irreversible catastrophe."
Mr. Obama urged more than 90 global leaders gathered for a climate change summit in New York City to work together to combat the problem.
U.N. Secretary-General Ban Ki-moon called the summit, and opened the session Tuesday by saying it would be "morally inexcusable" not to act.
Officials hope to make progress toward a global climate treaty that governments plan to finalize during a December meeting in Denmark.
President Obama said the United States is "determined to act" and has put climate at the top of the diplomatic agenda with countries across regions, from China and India to Brazil and Mexico.
The U.S. leader said the security and stability of every nation are at stake.
Mr. Obama said "there should be no illusions" about how difficult it will be for world leaders to reach a climate change agreement during the Copenhagen meeting in December.
President Obama acknowledged that developed nations had caused much of the damage to the global climate, and said they also have the responsibility to lead the global fight against it. He said the United States was slow to recognize and respond to global warming, but he outlined a series of steps his administration is now taking to combat the problem.
The U.S. leader noted that rapidly-growing developing nations must do their part as well.