By Mark Kinver
Science and Nature reporter, BBC News
The international climate debate needs to embrace a "new way of thinking" to tackle the problem, UN Secretary General Ban Ki-moon has urged.
Mr Ban called on world leaders to unite on climate change
Too much time was being wasted arguing over "historical responsibilities" for past emissions, Mr Ban said.
He called for both industrialised and developing nations to focus on limiting future global greenhouse gas emissions.
Mr Ban added that he would convene a climate summit to help reach consensus on a global climate action plan.
"It is time for new thinking," he told an audience at Chatham House, the international think-tank based in London, UK. "This is an agenda that really affects the whole of human kind.
"I promise that this challenge and what we do about it will define us," he said.
Breaking the deadlock
Recent attempts to reach a global agreement to replace the Kyoto Protocol, which expires in 2012, have ended in failure.
The global climate treaty requires industrialised nations to reduce their greenhouse gas emissions by 5.2% from 1990 levels, but the US and Australia have refused to ratify it.
President Bush's administration called the scheme "fatally flawed", partly because it did not require developing countries, including China and India, to commit to emissions reductions.
The idea of making developing nations enforce emissions caps has also faced opposition.
In June, China published its first national plan to curb climate change but it stopped short of backing a limit.
Ma Kai, chairman of China's National Development and Reform Commission, said: "We must reconcile the need for development with the need for environmental protection."
But he added that rich countries were responsible for most of the greenhouse gases produced over the past century, and had an "unshirkable responsibility" to do more to tackle the problem.
"The international community should respect the developing countries' right to develop," Mr Ma observed.
Mr Ban, in his first speech in the UK since becoming UN secretary general, warned that arguing over the legacy of past emissions only wasted time.
"I have been advised by many experts that if we act now - since we have the resources and heightened awareness - we can reverse it," he said.
"Then we can give a much more prosperous planet Earth to our great, great, grandchildren.
"What I would like to stress is rather than looking at past historical responsibilities, we need to look at historical responsibilities in the future.
"To build on the current momentum, I am going to convene a high-level UN General Assembly debate on 24 September."
He said that the outcomes from this meeting would feed into the UN climate negotiation process.
The UN Framework Convention on Climate Change (UNFCCC) will hold its next meeting in Bali towards the end of the year.
"Business as usual is no longer an option - we must reach complete agreement," he told the audience in central London.