I am convinced that mankind's only chance of survival is the discovery of an efficient, renewable source of energy. The rationale is simple: relying on fossil fuels means that sooner or later we will run out of energy. Ever since the Industrial Age, humans started relying on energy consumption as a need nearly as fundamental as the need to consume food. Energy translates to money (if you've been to Dubai, you will agree) and, indirectly, to power. And, most importantly, the shortage of energy, just as the shortage of any resource, leads to competiton for what's left, and ultimately wars.
It seems to me that assuming the current population levels, the energy scarcity will begin to threaten mankind's progress, and, ultimately, existence (energy is the most fundamental resource- if we run out of it, it's game over. If we have plenty of it, we can probably ensure we'll have enough of other resources, such as food).
What we should be doing now to avoid extinction, then, is collaborating to discover such an efficient and renewable energy source.
Why is efficiency a factor? Our progress depends on how quickly we can generate energy, and-more importantly-how effectively we can store it. Fossil fuels are a relatvely efficient energy source which can be stored quite well. Our current endeavors in the space of renewable sources fall short of this requirement-solar cells generate very little power for ther size, batteries aren't nearly as good at storing energy as, say, oil.
The Sun provides us with-for all intents and purposes-unlimited energy. The way I see it, we have two options: get better at taking the Sun's energy, or mimic its process. Scavenging it efficiently, and storing it, continues to be a challenge, but we have made some progress on fusion.
I'm optimistic and believe that we'll get smarter faster than we'll use up our current energy sources. But one should not get complacent- the future looks very dim if we fail.