Reading some of the answers in this thread, I think I would put all my resources into a global education program.

In my eyes the greatest challenge is to find a way to enable humanity to live in a way that does no longer destroy the ecosystem it relies on.

Unfortunately, the solution won't be just technological but rather social, educational and political.

We must find ways to stop overconsumption, overpopulation and to teach children (and people in general) the value of our natural environment.