Stephen said "100 years"..
What can't we do in 100 years? Think about where we were 100 years ago and where we are now... The massive advancements we made! Why wouldn't we be able to invent an easy solution to the heating of the Earth problem?
Ofcourse it won't be easy to invent an easy solution, but I'm quite sure 100 years is enough for us to think of one and actually do it!
"And if we don't succeed?" Ofcourse there exists the possibility of us not succeeding in saving the planet.. That means we have to get an other planet. We can go to a planet just like Earth through a Wormhole and save us all!
There are some inventions that have made really to help us solve global warming but these solutions are nothing compared to how we destroy our planet by releasing a lot of greenhouse gasses but I'm sure that people would come up a better invention to save this planet since they knkw for sure that when Earth die so as the entire beings residing on it.