It is unclear, as yet, what will happen when the first commitment period of the sole treaty setting out legally binding emissions targets expires at the end of 2012.
The plan was to come up with a successor to the Kyoto Protocol, but with Russia, Japan and Canada all saying they will not sign up to a new round of cuts unless emerging economies such as China, India and Brazil get on board, that is not looking very likely.
The US, which has always refused to ratify Kyoto, is one of a number of countries which favors an approach based upon voluntary commitment.
Developing countries and many environmental groups observing the talks consider voluntary pledges to cut emissions a step backwards.
"We need political commitment by the end of the year at the latest," Jan Kowalzig, climate expert with the German branch of the charity Oxfam, told Deutsche Welle. "And if that is not forthcoming, it will spell the end of the Kyoto Protocol."
Christiana Figueres, executive secretary of the UN Framework Convention on Climate Change (UNFCCC), has also indicated that it may already be too late to come up with a successor to Kyoto before the existing treaty runs out.
"Even if they were able to agree on a legal text for a second commitment period that requires an amendment to the Kyoto Protocol, it requires legislative ratifications on the part of three-quarters of the parties, so we would assume that there's no time to do that between Durban and the end of 2012," she told reporters at the Bonn talks, which run until mid-June.
Referring back to the climate summit in Cancun last December, when governments agreed to limit global warming to two degrees above pre-industrial levels, she said a target temperature range had been set, and that it was now essential to work towards it.
"Now, more than ever, it is critical that all efforts are mobilized towards living up to this commitment," Figueres said.
Worldwide levels of CO2 emissions have increased since that pledge in Mexico last year. A recent International Energy Agency (IEA) report says emissions reached a record high in 2010, and that if more is not done to bring them down, the two-degree target will be beyond reach.
On Monday, the European Union said that although it was willing to back a second round of Kyoto, it would be wrong for other parties to the protocol to assume that there would be no conditions attached.
"That is not the case," chief negotiator Artur Runge-Metzger said, adding that the EU would only renew its Kyoto vows if there were "also agreement on the other side towards an agreement that covers all those major economies at the same time."
As EU countries are only responsible for 11 or 12 percent of emissions, he said the Durban talks would need to find a solution for the remaining 88 or 89 percent.
Another issue discussed at Cancun, for which the details have yet to be worked out, is the creation of a 100-billion-dollar "green fund" to help developing countries deal with climate change.
Exactly how the money will be generated is just one of the unanswered questions around the fund.
Jan Kowalzig doesn't rate the idea of voluntary contributions, which he believes makes it too easy for wealthy countries to reclassify development aid as climate money, without having to cough up extra cash.
"We have to be honest about what we have promised, and then we have to learn what it means for the future," Kowalzig said, adding that it is easy to create a situation where there is suddenly not enough money for fighting poverty.
"We need reliable sources of new, additional money."
Oxfam's suggestion is for a climate levy on international air and sea travel to be paid directly into the "green fund," and although no decision will be taken over the next ten days in Bonn, Figueres says progress is being made behind the scenes.
"Not all the work is being done in these sessions themselves, there is also work that is being done for example on the green climate fund, outside these large processes by very focused groups," she explained.
In the case of the green fund, a transitional committee has already met twice and is meeting again in Japan next month to continue on the slow road of climate action.
Editor: Nathan Witkop