Hydrogen and its potential to be a clean fuel are once more in the news as governments and industries attempt to reduce greenhouse gas emissions to net zero.
What is hydrogen energy? How can it be used to replace fossil fuels?
Roger Harrabin, BBC's energy- and environment analyst, explains.
Read more about the climate summit
If climate change is to be controlled, the COP26 global climate summit will take place in Glasgow in November. It will be important to make significant changes in our daily lives by asking nearly 200 countries for their plans to reduce emissions.
