It has long been known that certain human activities, such as burning fossil fuels, release by-product gases into the atmosphere. Some of these gases, including carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4), are commonly called greenhouse gases (GHGs) because they trap heat at and near the earth's surface, causing the planet to get warmer. This effect is similar to that seen in a greenhouse, hence the name, "greenhouse effect." The greenhouse effect occurs naturally and is essential to keeping the earth warm enough to sustain life. However, according to the Intergovernmental Panel on Climate Change (IPCC), increased pollution due to industrialization, population growth, and deforestation has changed the mixture and amount of greenhouse gases in the atmosphere. This variation has increased the amount of heat that is trapped, resulting in the phenomenon known as global warming - an increase in average earth surface and ocean temperatures that has occurred over the last century.