Four years after Donald Trump withdrew the US from the Paris climate accord, his successor Joe Biden has put the country firmly back in the fight against climate change. He has unveiled an ambitious plan that aims to achieve net zero emissions by 2050. To do this, Biden plans to boost the development of hydrogen. Most of the hydrogen consumed today is extracted from fossil fuels. But in California, researchers, manufacturers and startups are trying to implant carbon-free or "green" hydrogen, which would be a revolutionary step forward. Our correspondents report.
Programme prepared by Jennie Shin.
