You have the refugee crisis triggered by Syria. That's got a lot of costs associated with it. Domestically, budgets are incredibly tight because the economy's not generating the growth that makes for easy trade-offs.

Other paths would include making nuclear fission cheap enough and safe enough that people broadly embrace it, so that could be scaled up.

Make sure people get educated, help out with health emergencies. Those things, the government should do. That's 96 per cent of the economy, those two sectors.

It's fantastic that Microsoft in the cloud space is one of very few companies that's got the critical mass, the particular emphasis on helping business customers get up to that cloud with all the unique requirements they have. It's very exciting.

My success, part of it certainly, is that I have focused in on a few things.

Energy is actually harder; it takes more time to get a product, but if you do it's a very, very big market and the constraints of doing that in a clean way are more obvious all the time.

It is a high bar to say that it's more fun than working on software because the work at Microsoft that both Melinda [Gates] and I did was thrilling. We were making breakthroughs and empowering people.