Everyone is focusing on the effects of climate change, while Musk seems to have already started finding the opportunities. In our lifetimes, 87% of the world's energy sources will change from fossil-based to other[1]. That's a $5+ trillion per year economy that will move from one source per year to another[2]. About $20 trillion worth of already purchased fossil assets will have be stranded and left in the ground[3].
Musks is trying to be a big player in making the transition happen. There's a double-digit-trillion dollar opportunity for new players in energy, and that's what Musk is aiming for.
[1]: http://www.pvsolarreport.com/the-next-internet/
[2]: http://tonyseba.com/portfolio-item/solar-trillions/
[3]: https://en.wikipedia.org/wiki/Carbon_bubble