Greenhouse gas

A diagram of the greenhouse effect. Energy flows between space, the atmosphere, and Earth's surface. Energy exchanges are written in watts per square meter (W/m²).

Greenhouse gas reflects radiation that the Earth emits, preventing it from escaping into space. This occurrence is known as the "greenhouse effect".

Many greenhouse gases are natural, with water vapor being the most common and responsible for most of the greenhouse effect on Earth. Other significant greenhouse gases include carbon dioxide, methane, nitrous oxide, chlorofluorocarbon (CFCs) and ozone.

Without greenhouse gases, life as we know it on earth would likely not be possible as heat is essential for sustaining life. Natural emissions of greenhouse gases vary, and events like massive volcanic eruptions such as those which created Siberian Traps around a quarter billion years ago, might have released enough gases to contribute to the Permian–Triassic extinction which caused to destructive effects on life on earth.

However, humans are introducing additional greenhouse gases to the atmosphere, leading to an enhanced greenhouse effect and increase in the planet's average temperature. The most significant greenhouse gas that contributed by humans is carbon dioxide, currently composing approximately 0.04% of the atmosphere. Human activities like burning fossil fuel such as oil, coal and natural gas for transportation, energy production and industrial processes are the main sources of carbon dioxide emission. The major contributor to these emissions is the industrial sector. ^[1] The Food and Agriculture Organization has reported that emissions associated with livestock, contribute to 7.1 gigatons (GT) of carbon dioxide equivalent (CO₂-eq) per year, accounting for 14.5% of all human-caused greenhouse emissions.^[2] This exceeds the 13% that contributed by global transportation (including cars and planes) each year.^[3]

Water vapor is the most abundant greenhouse gas, and it responds to climate changes. When the atmosphere is warm, it holds more water vapor, which increase the probability of cloud formation and precipitation.

In addition to burning fossil fuels, human activities also reduce the earth's capacity to absorb carbon dioxide from the atmosphere by deforestation. Methane emission is also increase due to the activities like raising cattle and other farm animals, including as geese, turkeys, pigs, chickens, and sheep.^[4] Scientists have shown that producing 1 kg of beef generated more CO₂ emissions than a three-hour drive with all household lights on.^[5] Further, human activity introduces water vapor to the atmosphere through increased evaporation from cooling towers in thermal cycle power plants and creation of artificial lakes which contributes to the global warming.

Greenhouse Gas Media

Greenhouse gases trap some of the heat that results when sunlight heats the Earth's surface. Three important greenhouse gases are shown symbolically in this image: carbon dioxide, water vapor, and methane.
Physical drivers of global warming that has happened so far. Future global warming potential for long lived drivers like carbon dioxide emissions is not represented. Whiskers on each bar show the possible error range.
Atmospheric absorption and scattering at different wavelengths of electromagnetic waves. The largest absorption band of carbon dioxide is not far from the maximum in the thermal emission from ground, and it partly closes the window of transparency of water—explaining carbon dioxide's major heat-trapping effect.
Longwave-infrared absorption coefficients of primary greenhouse gases. Water vapor absorbs over a broad range of wavelengths. Earth emits thermal radiation particularly strongly in the vicinity of the carbon dioxide 15-micron absorption band. The relative importance of water vapor decreases with increasing altitude.
Concentrations of carbon monoxide in April and October 2000 in the lower atmosphere showing a range from about 50 parts per billion (blue pixels) to 220 parts per billion (red pixels) and 390 parts per billion (dark brown pixels).
Atmospheric gases only absorb some wavelengths of energy but are transparent to others. The absorption patterns of water vapor (blue peaks) and carbon dioxide (pink peaks) overlap in some wavelengths.
The radiative forcing (warming influence) of long-lived atmospheric greenhouse gases has accelerated, almost doubling in 40 years.
This figure shows the history of atmospheric carbon dioxide concentrations as directly measured at Mauna Loa, Hawaii since 1958. This curve is known as the
CH4 measured by the Advanced Global Atmospheric Gases Experiment (AGAGE) in the lower atmosphere (troposphere) at stations around the world. Abundances are given as pollution free monthly mean mole fractions in parts-per-trillion.