[mcv]

Instead of dividing them into grey and green, we should rank them in red, yellow and green.

Red energy sources are the ones we immediately need to stop using: coal and oil.

Yellow energy sources are the ones we should stop using only if we can safely do so, but if we can't (and we can't, right now) we should continue using them: gas and nuclear.

Green energy sources are where we really need to go.