JOHANNESBURG, South Africa - The hard-won deal at a U.N. global climate conference in South Africa keeps talks alive but doesn't address the core problem: The world's biggest carbon polluters aren't willing to cut emissions of greenhouse gases enough to stave off dangerous levels of global warming.

With many scientists saying time is running out, a bigger part of the solution may have to come from the rise of climate-friendly technologies being developed outside the U.N. process.

Scientists say that if levels of greenhouse gases continue to rise, eventually the world's climate will reach a tipping point, with melting of some ice sheets and a catastrophic rise of several feet in sea levels.

They cannot pinpoint exactly when that would happen, but the two-decade-long climate negotiations have been focused on preventing global temperatures from rising more than 2 degrees Fahrenheit above current levels by the end of this century.

A report released before the Durban talks by the U.N. Environment Program said greenhouse-gas emissions must peak before 2020 for the world to have a shot of reaching that target. It said that is doable only if nations increase their pledged cuts in emissions.

In Durban, they did not.

Sunday's deal extends by five years the Kyoto Protocol, the 1997 agreement that has binding emissions targets for some industrial countries but not for others - including China, one of the world's two biggest carbon polluters. The other is the United States, which declined to sign the protocol.

The Durban agreement also envisions a new accord with binding targets for all countries to take effect in 2020. And it sets up the bodies to collect, govern, and distribute tens of billions of dollars to poor countries suffering the effects of climate change.

Climate talks have been bogged down by rifts between rich and poor, between fully industrialized nations and emerging economies, about how to share the burden of reducing greenhouse emissions.

Meanwhile, heat-trapping gases from the burning of fossil fuels continue to pour into the atmosphere. Figures from the U.N. weather agency show the three most powerful greenhouse gases reached record levels last year and were increasing at an ever-faster rate.

And the U.S. National Oceanic and Atmospheric Administration says the total heat-trapping effect from major greenhouse gases has increased 29 percent since 1990, the benchmark year in the climate talks.

Some say that the diplomatic effort to deal with the climate issue has already failed, and that the answer lies in the development of green technologies outside the U.N. process.

Roger Pielke Jr. of the University of Colorado said treaties and timetables don't reduce emissions.

"Technology reduces emissions," he said. "International agreements are simply a means to stimulating technological innovation. In the climate debate, we have confused ends and means."

Despite technological advances, renewable energy sources such as solar and wind power face big challenges, struggle to compete on cost and efficiency with fossil-fuel-based energy, and still represent only a small part of the energy mix in the United States. And in some cases it is fossil-fuel production that is benefiting from technological innovation, with new techniques making it easier to drill for oil in deep water and for gas in underground shale beds.