The prime minister has warned world leaders there can be no more "drift" on policies to tackle climate change.
Ahead of global talks to take place in Copenhagen in December, Gordon Brown set out a series of proposals which could form the basis for an agreement.
These included a $100bn annual fund for climate action by 2020, and a pledge that expenditure on helping poorer countries adapt to global warming should come on top of other development assistance.
Brown called for world leaders to agree on a treaty which would see rich countries provide extra funding to help developing countries adapt to climate change.
"I propose we take a working figure for this purpose of about $100bn per annum by 2020," said Brown.
"If we are to achieve an agreement in Copenhagen I believe we must move the debate from a stand-off over hypothetical figures."
Speaking at London Zoo, the prime minister said it was essential to reach a global agreement on carbon emission cuts to cap the increase on the global temperature
Brown called on the countries to set a limit of two degrees centigrade on global warming.
"We cannot in good conscience plan for the world to exceed that limit," he said. "So our goal must be 'no more than two degrees'."
The prime minister said part of the fund, worth £60bn, could be funded with revenue raised from aviation and maritime emissions.
"So we must help the developing countries adapt to the changes in climate which are already now occurring and which over the next few decades, however much we cut emissions, we cannot now avoid," Brown said.
And to make room for economic growth in the developing world, countries will need to reduce their own emissions by at least 80 per cent by 2050.
The speech came ahead of a key vote in the US House of Representatives on whether to proceed with climate change legislation for America.
Greenpeace chief scientist Doug Parr said the prime minister had shown an understanding of the scale of action needed from world leaders at Copenhagen.
"By becoming the first major leader to put a figure on how much money is needed he has shown signs of leadership on climate change that have so far been sorely lacking," Parr said.
