Energy for Everyone
So in summary I believe that if you had to pick one issue that’s more important than any other single issue, it is energy. You could have picked any issue, but energy is something we can do something about, and if we do it, we can affect positively most of the other problems facing us.
The task would be supplying energy for ten billion people, and let’s get it clean, cheap, and continually available. If there’s an answer, it will be some manipulation of matter on the nanoscale that will give it to us—something I like to call nanotechnology.