US president Barack Obama has led the way as world leaders and industry chiefs seek to build momentum for a new international deal on climate change.
Mr Obama told a United Nations summit on greenhouse gas emissions that the US was "determined to act" on global warming.
Chinese president Hu Jintao said his country would increase renewable power, energy-saving programmes and forest cover to tackle its emissions.
Mr Obama insisted the United States was serious about combating global warming and declared: "We are determined to act."
He added: "The journey is hard. And we don't have much time left to make it,. We understand the gravity of the climate threat. We are determined to act. And we will meet our responsibility to future generations."
Mr Obama said his administration had made the "largest-ever" American investment in renewable energy. And he called on other nations -- the rich and the developing countries alike -- to rise to the challenge. He said undertaking costly environmental clean up work is difficult at a time when the world is trying to recover from a recession, but that it has to be done.
"All of us will face doubts and difficulties in our own capitals as we try to reach a lasting solution to the climate challenge," Mr Obama said. "But difficulty is no excuse for complacency."
The comments by the presidents of the two biggest emitters of the greenhouse gases which cause climate change came after a call to action on the issue by more than 500 global businesses.
Heads of companies including big British names such as British Airways, Virgin, BP and Shell, published their "Copenhagen Communique" at the UN summit, which was convened by UN secretary general Ban Ki-moon in New York.
The report warned that a failure to agree a new climate treaty at crunch talks in the Danish capital in December would worsen the current economic situation. But an agreement based on the science of climate change, with commitments for deep and immediate cuts from industrialised countries, would "deliver the economic signals that companies need if they are to invest billions of dollars in low carbon products, services, technologies and infrastructure", it said.