Energy is essential to life. Living creatures draw on energy flowing through the environment and convert it to forms they can use. Over time, many different sources of energy have been discovered, developed, used and in some cases, abused. Some energy sources, such as solar and wind (among others) are considered renewable, and therefore environmentally friendly, because they do not deplete the planet of valuable resources, nor do they contribute heavily to greenhouse gas emissions.
Other energy sources are cause for concern because they produce serious pollutants, specifically coal and petroleum (oil), which are both ubiquitous in the world of energy production. The burning of these, which produces power for electricity, emits CO2, NO3, ozone and other greenhouse gases that contribute directly to climate change. Scientists and researchers worldwide have worked for years to establish prevalence of cleaner, more renewable forms of energy in order to decrease human exacerbation of global warming and climate change.