Humans have overexploited natural resources to ensure energy supply. If current trends continue, fossil fuels will run out in decades. Even if all fossil fuels are used for energy, an increasing population and urbanization will strain them. Hydrocarbons—oil, coal, and natural gas—have been humanity's main energy source for a century. However, climate change and its effects on human health and well-being have greatly raised the demand for alternate energy sources. Over 80% of global energy comes from hydrocarbons. Fossil fuel production and consumption account for 89% of worldwide greenhouse gas emissions, including carbon dioxide. Power plant emissions, including primary and secondary pollutants, are detrimental to human health. PM 2.5 and PM 10 are major causes of early respiratory illness mortality, chronic bronchitis, upper and lower respiratory tract infections, and cardiovascular disease. Other thermal power plant fuel combustion byproducts such sulphur dioxide, nitrogen oxides, and volatile organic compounds cause more sickness. Thermal power plant emissions deplete ozone, causing respiratory illness, lung function, and recently, fatality. The most important factor in early air pollution deaths is fine particulate matter.