We will... Not sure how, but Humans will kill themselves! It's in our nature to bring havok and destroy everything that has made us to what we are today... We really are one fucked up species. However, if handled properly, we have much potential.
And I think that, in order to save mankind on the short-run, we should create something in the way of 'get as fast to the moon as possible', or the size of the 'manhatten-project' in order to gain full-out green-energy for the whole-wide-world!
So, unlimited resources and encourage people to build it as fast as possible!... You might think that's crazy now, but later on, mankind look back on a great achievement and a great U-turn in their ways of treating this planet, its flora and fauna, and itself!