Where is the hydrogen to power Japan zero-carbon society going to come from? The answer is "blue hydrogen". Make hydrogen from water using renewable energy and you get "green hydrogen". The problem is green hydrogen is really expensive. Instead, today most hydrogen is made from natural gas or even coal. That is cheap but it produces lots of greenhouse gases. However, if you capture those greenhouse gases and bury them in the ground, you are allowed to call it "blue hydrogen". This is exactly what Japan says it is going to do.