DURBAN, South Africa—For the first time, all major nations—developed and developing—have agreed to a roadmap that would combat climate change by reducing greenhouse gas emissions via an "outcome with legal force" that would not come into effect before 2020. The 194 countries negotiating here also agreed that such a universal plan must be completed by 2015 at the latest.

"I think we all realize they are not perfect," said Maite Nkoana-Mashabane, South African Minister of International Relations and Cooperation and President of the Durban U.N. Climate Change Conference late on the night of December 10, referring to the proposed agreements when the outcome was still in doubt. "We should not let the perfect become the enemy of the good and the possible."

What proved possible included an extension of the Kyoto Protocol for a period of either five or seven years (excluding Canada, Japan and Russia but adding nitrogen trifluoride, used in semiconductor manufacture, to the list of gases covered—CO2, methane, nitrous oxide, sulfur hexafluoride, perfluorocarbons), a Green Climate Fund to help low-income countries cope (albeit without any actual funds yet), an Adaptation Committee to coordinate such efforts globally, rules for a global program to reduce deforestation and how to monitor such deforestation, and a Climate Technology Center that will help launch projects to reduce greenhouse gas emissions. The Kyoto Protocol, which was set to expire at the end of 2012, set binding targets for 37 industrialized countries and the E.U. for reducing greenhouse gas emissions an average of five percent against 1990 levels. The U.S. never ratified the Kyoto Protocol, which starting going into force in 2008.

Ultimately, it took the most interested parties—the U.S., E.U., India, China and others—huddling on the floor of the plenary to strike a deal, largely by blurring the exact wording of what this new, potentially global effort might in fact be. "The United States saw an opportunity to break down the wall blocking adoption of binding commitments by the largest emitting developing countries and took advantage of that," says Jake Schmidt, international climate policy director at the Natural Resources Defense Council, a U.S.-based environmental group.

Of course, a similar action plan was agreed to in Bali in 2007 and collapsed in Copenhagen in 2009. And it is also clear—even to the negotiators who also agreed to be "informed" by the science expected from the International Government Panel on Climate Change's next assessment report in 2013—that neither the "Durban Platform for Enhanced Action" nor the extended Kyoto Protocol are equal to the task of restraining ever-rising greenhouse gas emissions.

In fact, the mitigation pledges collected under the ongoing Cancun Agreements, conceived during the 2010 climate talks, would lead to global average temperature rise of more than 2 degrees Celsius, according to multiple analyses—and may not lead to a peaking of greenhouse gas emissions this decade required to meet that goal. The Durban package will not change that. "Of course, the package is not the best we can do," Nkoana-Mashabane noted during negotiations early on December 11. "We must and we will do better."

But this new package does include for the first time all countries working towards a global reduction of greenhouse gases, whether developed or developing. It reaffirms that holding global warming to no more than 2 degrees C remains the goal of such international negotiations and launches a working plan to consider how ambitions might be raised, particularly in developed countries such as the U.S. that are responsible for the bulk of the greenhouse gases emitted worldwide in the past several centuries.

"Powerful speeches and carefully worded decisions can't amend the laws of physics," notes Alden Meyer, director of strategy and policy at the Union of Concerned Scientists. "The atmosphere responds to one thing, and one thing only: emissions. The world's collective level of ambition on emissions reductions must be substantially increased, and soon."