China is expected to announce tough new carbon emission targets UN Secretary General Ban Ki-moon has called for urgent action on climate change, saying negotiations on reducing emissions were proceeding too slowly.
He said failure to reach agreement at December's climate talks in Copenhagen would be "morally inexcusable".
He was speaking at a UN meeting attended by about 100 world leaders in New York to revitalise the talks.
Attention is likely to focus on Chinese President Hu Jintao, who is expected to unveil new steps to tackle emissions.
The summit in Copenhagen is aimed at approving a global climate change treaty.
Negotiators are trying to agree on a replacement for the Kyoto Protocol to limit carbon emissions.
Chinese targets
Mr. Ban called the meeting an attempt to inject momentum into the deadlocked climate talks.
"Your decisions will have momentous consequences," he told the assembled leaders.
"The fate of future generations, and the hopes and livelihoods of billions today, rest, literally, with you," he added.
United States President Barack Obama said Americans understood the gravity of the climate threat and were determined to act, but there was much more work to be done.
"If we are flexible and pragmatic; if we can resolve to work tirelessly in common effort, then we will achieve our common purpose: a world that is safer, cleaner, and healthier than the one we found; and a future that is worthy of our children," he said.
According to the BBC's UN correspondent, Barbara Plett, discussions have stalled because rich nations are not pledging to cut enough carbon to take the world out of danger, while poorer countries are refusing to commit to binding caps, saying this would prevent them from developing their economies.
China's role is crucial, because it is both an emerging economy and a big polluter, our correspondent says.
The UN's chief climate change negotiator, Yvo de Boer, says he expects an important announcement from Beijing during the meeting.
"China domestic policy is already very ambitious but yes I do expect something dramatic," he said.
President Hu Jintao is expected to announce "carbon intensity targets" aimed at making Chinese industry more efficient, so that less carbon is produced per unit of energy generated.
China has already leapfrogged the United States to become the world's biggest wind power market, and is a growing force in solar power - and analysts say President Hu may advance the country's renewable energy targets even further.
But the BBC correspondent in Beijing, Quentin Sommerville, says it is unlikely that the Chinese will agree to a cap on their carbon emissions.
Despite all its advances in green technology, China still gets 70% of its energy from coal - and as its economy increases, this means yet more growth in greenhouse gases, our correspondent says.
Pressure on US
There is also concern about the world's other big polluter, the United States.
President Barack Obama has recognised climate change as a pressing issue, unlike the previous administration, our UN correspondent says.
He has already announced a target of returning to 1990 levels of greenhouse emissions by 2020, but critics say Washington is moving too slowly on legislation which does not go far enough.
President Obama is currently dogged by domestic issues such as the economy and healthcare reforms, but his speech to the UN meeting will still be watched for signs he is willing to fulfil his pledge to take the lead in reaching a global carbon deal.
A demonstration of political will by both China and the US will be important in breaking the deadlock in negotiations, correspondents say.
China and the US each account for about 20% of the world's greenhouse gas pollution from coal, natural gas and oil.
The European Union is responsible for 14%, followed by Russia and India with 5% each.
BBC News
He said failure to reach agreement at December's climate talks in Copenhagen would be "morally inexcusable".
He was speaking at a UN meeting attended by about 100 world leaders in New York to revitalise the talks.
Attention is likely to focus on Chinese President Hu Jintao, who is expected to unveil new steps to tackle emissions.
The summit in Copenhagen is aimed at approving a global climate change treaty.
Negotiators are trying to agree on a replacement for the Kyoto Protocol to limit carbon emissions.
Chinese targets
Mr. Ban called the meeting an attempt to inject momentum into the deadlocked climate talks.
"Your decisions will have momentous consequences," he told the assembled leaders.
"The fate of future generations, and the hopes and livelihoods of billions today, rest, literally, with you," he added.
United States President Barack Obama said Americans understood the gravity of the climate threat and were determined to act, but there was much more work to be done.
"If we are flexible and pragmatic; if we can resolve to work tirelessly in common effort, then we will achieve our common purpose: a world that is safer, cleaner, and healthier than the one we found; and a future that is worthy of our children," he said.
According to the BBC's UN correspondent, Barbara Plett, discussions have stalled because rich nations are not pledging to cut enough carbon to take the world out of danger, while poorer countries are refusing to commit to binding caps, saying this would prevent them from developing their economies.
China's role is crucial, because it is both an emerging economy and a big polluter, our correspondent says.
The UN's chief climate change negotiator, Yvo de Boer, says he expects an important announcement from Beijing during the meeting.
"China domestic policy is already very ambitious but yes I do expect something dramatic," he said.
President Hu Jintao is expected to announce "carbon intensity targets" aimed at making Chinese industry more efficient, so that less carbon is produced per unit of energy generated.
China has already leapfrogged the United States to become the world's biggest wind power market, and is a growing force in solar power - and analysts say President Hu may advance the country's renewable energy targets even further.
But the BBC correspondent in Beijing, Quentin Sommerville, says it is unlikely that the Chinese will agree to a cap on their carbon emissions.
Despite all its advances in green technology, China still gets 70% of its energy from coal - and as its economy increases, this means yet more growth in greenhouse gases, our correspondent says.
Pressure on US
There is also concern about the world's other big polluter, the United States.
President Barack Obama has recognised climate change as a pressing issue, unlike the previous administration, our UN correspondent says.
He has already announced a target of returning to 1990 levels of greenhouse emissions by 2020, but critics say Washington is moving too slowly on legislation which does not go far enough.
President Obama is currently dogged by domestic issues such as the economy and healthcare reforms, but his speech to the UN meeting will still be watched for signs he is willing to fulfil his pledge to take the lead in reaching a global carbon deal.
A demonstration of political will by both China and the US will be important in breaking the deadlock in negotiations, correspondents say.
China and the US each account for about 20% of the world's greenhouse gas pollution from coal, natural gas and oil.
The European Union is responsible for 14%, followed by Russia and India with 5% each.
BBC News