Gas emissions are any gaseous material released, either naturally or artificially, into the atmosphere. These gas emissions exist in a variety of forms: most notably water vapor, carbon dioxide, methane, nitrous oxide and ozone. Each of these substances, while already existing in the atmosphere at certain levels, can be increased through various means, such as the burning of fossil fuels or the eruption of a volcano. The effects of these gas emissions come in the form of the greenhouse effect. Each of these gases absorb radiation in the atmosphere, increasing the temperature of the Earth.
Different gases have different effects on the atmosphere and exist in different quantities. For example, methane is one of the strongest absorbers of radiation, while carbon dioxide is not. However, the level of carbon dioxide from gas emissions is much more prevalent than methane, so its effect is much stronger overall. This atmospheric warming is needed to maintain present conditions on the planet. Earth's surface temperature would be approximately 59°F (about 33°C) colder if these gases were not present in the atmosphere.
Water vapor is the most prevalent gas emission on the planet and accounts for the largest percentage of impact to the greenhouse effect. This is generally not caused by humans in abundance. Two percent of the atmosphere is composed of water vapor, including the clouds, most of which stems from simple gas emission caused by evaporation. This percentage, according to the Environmental Health Center of the National Safety Council, accounts for 66 percent of the greenhouse effect.
Using ice core samples, scientists have determined that greenhouse gas emissions have changed over time. 500 million years ago, the carbon dioxide level was ten times as prevalent as it is today. High concentrations of greenhouse gases continued until the modern era. Humans now live in the Holocene era, which began with the end of the last ice age approximately 10,000 years ago. During this period, gas emissions from naturally-occurring sources such as volcanoes remained relatively stabilized, accounting for only a one percent fluctuation on the atmosphere.
Since 1750, however, the gas emissions from humans have increased significantly, due to the onset of the Industrial Revolution. Prior to this time, carbon emissions were roughly 280 parts per million (ppm). This number has risen steadily since then to arrive at 387 ppm by the early 21st century. These greenhouse gas emissions stem primarily from the burning of fossil fuels, deforestation, chlorofluorocarbons used in refrigeration and fertilizers. Each of these culprits has been targeted during the late 20th and early 21st century by the “green movement,” an effort to reduce carbon emissions.