For the next century, my generation's greatest challenge will be dealing with our energy sources. Energy is what drives everything in our society. The food we eat, the gas we put in our cars, as well as the electricity we use to turn on our lights - all originating from fossil fuels that were created from condensed sunlight millions of years ago. For millions of years, the Earth only had the available energy source of the sunlight to feed our societies' advancement.
During the 18th century that situation changed when the Industrial Revolution began using coal to fire industry and machinery to do the work of thousands of men. Shortly after the Civil War in the 1860s, oil was first utilized in this new industrialized society. America became the current day Saudi Arabia of oil exports up until the 1970s. Unfortunately for us, becoming the biggest exporter also made us the biggest user of oil. We currently have 5% of the population of the planet but utilize 25% of all the oil that the world consumes - roughly 20 million barrels of oil a day (though less since the recession).