Global warming

The majority of the world’s energy needs are met by burning hydrocarbon-based fossil fuels. Addition to requiring non-renewable natural resources that will eventually be depleted, this method of energy production produces greenhouse gases that contribute to climate change, releases toxic gases that comprise to smog that plagues cities, and requires expensive and often highly-polluting methods of fuel extraction, refining, and transport. Some of these problems have grown more pressing as fossil fuels have become scarcer, requiring drilling in more remote locations, use of less-ideal raw materials such as tar sands that require more intensive processing, and increasingly complex extraction techniques such as fracking.