Instead of using the money to research renewable or more efficient energy production, reduce pollution etc his foundation uses the money for vaccines and health services which surprisingly has as target, as he says in a ted video (link below), to decrease human population which he sees it as the major problem of today.

https://www.youtube.com/watch?v=JaF-fq2Zn7I&t=278&cc_load_po...

"The world today has about 6.8 billion people. That's headed up to about 9 billion. Now if we do a really great job on new vaccines, health care, reproductive health services, we could lower that by, perhaps, 10 or 15%"