Climate change: Obama launches Clean Power Plan to cut emissions

US President Barack Obama has urged his country to take its "most important step" to tackle to climate change, as he outlined proposals to cut carbon emissions.

The president's Clean Power Plan aims to cut greenhouse gas emissions from US power stations by nearly a third by 2030, by placing significant emphasis on wind and solar power and other renewable energy sources.

But opponents in the energy industry have accused him of declaring a "war on coal" and have vowed to fight the plan.

Science Editor David Shukman reports.