Previous climate change conferences in Copenhagen in 2009 and Cancun in 2010 ended without a plan for a new global deal, and time has run out to get a binding treaty in place when the first phase of the Kyoto Protocol expires at the end of 2012.
Everybody needs to have signed up by 2015, Artur Runge-Metzger told Reuters on Friday in an interview. Ratification would take several years more after that.
Pending a new global deal, there would be a transition period in which the Kyotol mechanisms would still apply and the EU would carry on leading efforts to cut emissions, he said.
So far the world is failing to reduce carbon emissions sufficiently to contain global warming within the limit of 2 degrees Celsius that scientists say is necessary to avoid the worst effects of climate change.
Runge-Metzger said the task would only get harder as carbon emissions need to be cut by 80 to 95 percent by 2050, compared with the collective commitment by developed countries for a 5.2 percent reduction from 1990 levels under the first phase of Kyoto.
Pledges on the table from Cancun totalled a roughly 60 percent reduction, which would translate into capping global warming at 3 to 4.5 degrees, Runge-Metzger said.
At the start of this week, the EU declared its openness to agreeing a second Kyoto commitment period after the first ends, but said it must have guarantees that other carbon emitters would also join in at some point.
Only developed nations signed the original pact in 1997. The United States never ratified it, and developing countries have become major emitters, with China overtaking the United States to become the world's biggest producer of carbon.
Runge-Metzger said it was crucial to avoid a Catch 22 situation, in which China said it would only sign when the United States did and vice versa.
They will have to go through the gate together, he said.
Monday's environment council also sought to address the issue of Kyoto allowances to produce greenhouse gases, known as Assigned Amount Units (AAUs), but after hours of debate it came up with only vague wording.
The issue is divisive because countries holding on to large amounts of spare allowances could sell them to nations with shortfalls.
Monday's conclusions said only that the surplus of AAUs could affect the environmental integrity of the Kyoto Protocol if the issue is not addressed appropriately.
Runge-Metzger said the European Union would have to undergo intensive debate on AAUs between now and Durban to resolve divisions within it on how much of the surplus could be carried beyond 2012.
This is an issue that's under negotiation and that has to be resolved. What we have on the table are a few words on how we can address this issue, he said.
Runge-Metzger was speaking on the sidelines of a round-table in Brussels to find common ground between the EU and the African Union.
Poorer nations are eager for the developed world to agree to deep cuts to emissions and to financial aid to help developing nations adapt to climate change.