While announcing his plan to spend $2 billion of his own wealth on green energy during an interview with The Atlantic, the Microsoft founder called on fellow billionaires to help make the US fossil-free by 2050 with similar philanthropy.

He said:

There's no fortune to be made. Even if you have a new energy source that costs the same as today's and emits no CO2, it will be uncertain compared with what's tried-and-true and already operating at unbelievable scale and has gotten through all the regulatory problems.

Without a substantial carbon tax, there's no incentive for innovators or plant buyers to switch.