It feels like within the next 20 years we are going to have a good handle on “green” power to fixed locations. The tricky piece we have left is how do we move people and freight over long distances.

EVs can do a decent job of transporting a few people a short distance, but aircraft and long distance freight has a whole other set of issues.

Look at container ships, one of the biggest polluters and sources of carbon on the planet. How do you remove the need for massive amounts of diesel on those?

How about passenger and air freight? How do we eliminate all the CO2 from jet fuel? In the US we are terrible at infrastructure, but do we invest in a super-train system?

This is likely the next big challenge.