California's newly adopted low-carbon fuel standard may mark the beginning of the end of ethanol's coveted status as the sole US alternative motor fuel.

The US state with the most cars late on Thursday approved the world's first-ever regulations to slash emissions of planet-warming carbon dioxide from vehicle fuels.

The world's forests are at risk of becoming a source of planet-warming emissions instead of soaking them up like a sponge unless greenhouse gases are controlled, scientists said.

Deforestation emits 20 percent of the world's carbon dioxide when people cut and burn trees, but standing forests soak up 25 percent of the emissions.

As the world tries to forge a new treaty to slow global warming, care must be taken not to spark trade conflicts between rich and developing countries, a key U.S. lawmaker said on Thursday.

"We clearly we do not want to trigger a trade war," Ed Markey, a Democrat who heads the House climate change committee, told reporters in a teleconference.

U.S. start-up Joule Biotechnologies hopes to make commercial amounts of motor fuel by feeding engineered organisms high concentrations of carbon dioxide and sunlight, its top executive said.

The United States could save about $600 billion in energy costs by 2020 if it hiked annual efficiency spending about five-fold, business consultants McKinsey and Co said in a report on Wednesday.

Alternative energy jobs can provide vocations across many sectors of the economy but policy to spark them can take years to develop, U.S. governors told a Senate committee on Tuesday.

Private U.S. company Tang Energy Group said on Friday a Chinese company has agreed to provide $300 million in financing for its wind power projects.

Steps President Barack Obama has taken on climate and clean energy have shown that the United States is getting ready to lead the world in fighting global warming, a White House official said on Tuesday.