The report says the world then needs to at least halve annual emissions of carbon dioxide by 2050 to keep global warming in check.
The panel agreed on measures to cut emissions, describing them as both achievable and affordable.
"The assessment says that it will cost less than 3 per cent of the global GDP," said report co-author Dr Joshi Roy,.
"So that’s really not very bad if you look into the kind of benefits that the world will be getting due to the lesser temperature. "
The wording of the agreement includes an implicit warning that the planet will not cope if developing countries aspire to the consumer lifestyles of those in the West.
Western nations are told to cut fossil fuel consumption and developing nations will have to find a cleaner path to prosperity.
The final text will controversially include a paragraph saying nuclear power could be part of the solution.
Germany tried to block this, but delegates said it was up to individual countries to decide.