You know why? It's because...
Our fossil fuels are disappearing
Without fossil fuels, we would lose almost 90% of the world's energy. This would result in a world where most of the people wouldn't have power. To prevent that. The first step would be to save energy so that less fossil fuels will be burnt.
If you want to make a change, go to this link: How can you make a difference. If still not convinced, then scroll down to see the benefits of conservation