The government wants a new globally binding climate deal to be operational by 2020 to reduce greenhouse gas emissions enough to keep world temperature rises to a limit of 2 degrees Celsius, the UK's minister for energy and climate change said.
The key thing is to have a deal to reduce emissions by 2020. As long as it is operating by then, that's fine, Chris Huhne told reporters on Thursday.
Negotiators from around the world will meet in Durban, South Africa, next Monday for two weeks to work on a new globally binding United Nations deal towards cutting emissions.
The aim is to keep within a global temperature rise limit of 2 degrees Celsius this century, a threshold scientists advise in order to avert wilder weather, crop failures, melting ice caps and major floods.
But only modest steps are expected despite warnings from scientists that extreme weather will likely increase as the planet warms, as rifts between countries on the matter continue.
An OECD report on Thursday warned global emissions will double in the next 40 years, resulting in a 3 to 6 degree increase in the average global temperature by the end of the century unless governments take decisive action.
We have to be guided by science. Emissions have to peak and then come down by 2020 if we have a realistic chance of holding the 2 degree Celsius (temperature rise) limit, Huhne said.
We think that means we need a global agreement by 2015, he added.
In Durban, the European Union as a whole is seeking a roadmap or mandate towards a global agreement being signed by all countries by 2015 or earlier.
Even if countries manage to agree on a deal by then, the time required for over 190 countries to process and ratify international agreements means the pact might not come into force until 2020 or later.
In some cases, the process may not take that long but it is one of the things we need to get sorted out (in Durban), Huhne added.
The eventual form of a global agreement might not mean that all countries will have the same type of emission cut commitments in five or 10 years' time, the minister conceded.
There will still be huge differences between countries then, just as there are now. China is not, and will not be, the same as Chad or India.
(Reporting by Nina Chestney; editing by Jason Neely)