Greenhouse effect
The greenhouse effect occurs when certain gases in the Earth's atmosphere (the air around the Earth) trap infrared radiation. This makes the planet become warmer, similar to the way a greenhouse becomes warmer.[1]
The most important greenhouse gases in Earth's atmosphere are: water vapor, carbon dioxide(CO2), and methane. When there is more greenhouse gas in the air, the air holds more heat. This is why more greenhouse gases cause climate change and global warming.[2]
The greenhouse effect is natural. It is important for life on Earth. Without the greenhouse effect, the Earth's average temperature would be around –18 or –19 degrees Celsius (0 or 1 degree Fahrenheit). Earth would be locked in an ice age. Because of the greenhouse effect, the Earth's actual average temperature is 14 degrees Celsius (57 degrees Fahrenheit).
The problem is that recently, the greenhouse effect has become stronger. This is because humans have been burning large amounts of fossil fuels, which releases carbon dioxide. Since carbon dioxide is a greenhouse gas, it has caused the planet to warm over the past 150 years.
About 10,000 years ago, before people started burning large amounts of fossil fuels, there were 260 to 280 parts per million (ppm) of carbon dioxide (CO2) in the atmosphere, but now there is over 400 ppm. Most scientists say that having 350 ppm or less is safe for the environment and that species on the planet can adapt to this level. Higher levels can make severe problems for animal and marine life that are already being seen today, such as ocean acidification.
The greenhouse effect was first proposed by Joseph Fourier in 1824. Mars, Venus and other planets with atmospheres also have greenhouse effects. The effect on Venus is especially strong because Venus has so much CO2. This is why Venus is hotter than Mercury, even though Mercury is closer to the sun. The first person to predict that carbon dioxide from the burning of fossil fuels (and other combustion processes) could cause global warming was Nobel Prize winner Svante Arrhenius.
Greenhouse Effect Media
Greenhouse gases allow sunlight to pass through the atmosphere and heat the planet, but then absorb and redirect some of the longwave radiation (heat) the planet emits.
Energy flows down from the sun and up from the Earth and its atmosphere. When greenhouse gases intercept radiation emitted by Earth's surface, they prevent that radiation from escaping into space, causing surface temperatures to rise by about 33 °C (59 °F).
How Template:CO2 causes the greenhouse effect.
The solar radiation spectrum for direct light at both the top of Earth's atmosphere and at sea level
Outgoing radiation and greenhouse effect as a function of frequency
Temperature needed to emit a given amount of thermal radiation.
Comparison of Earth's upward flow of longwave radiation in reality and in a hypothetical scenario in which greenhouse gases and clouds are removed or lose their ability to absorb longwave radiation—without changing Earth's albedo (i.e., reflection/absorption of sunlight). Top shows the balance between Earth's heating and cooling as measured at the top of the atmosphere (TOA).
The temperature at which thermal radiation was emitted can be determined by comparing the intensity at a particular wavenumber to the intensity of a black-body emission curve. In the chart, emission temperatures range between Tmin and Ts. "Wavenumber" is frequency divided by the speed of light).
Greenhouse gases (GHGs) in dense air near the surface intercept most of the longwave radiation emitted by the warm surface. GHGs in sparse air at higher altitudes—cooler because of the environmental lapse rate—emit longwave radiation to space at a lower rate than surface emissions.
Related pages
References
- ↑ IPCC, 2013: Annex III: Glossary [Planton S. (ed)]. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change Stocker T.F. D. Qin G.-K. Plattner M. Tignor S.K. Allen J. Boschung A. Nauels Y. Xia V. Bex and P.M. Midgley (eds). Cambridge University Press, Cambridge, United Kingdom and New York.
- ↑ Vaclav Smil (2003). The Earth's biosphere: evolution, dynamics, and change. MIT Press. p. 107. ISBN 978-0-262-69298-4.
Other websites
- The Climate Change Guide easy-to-understand information on the greenhouse effect
- Study of Ice Age bolsters carbon and warming link February 28, 2013 The New York Times
- Rutgers University: Earth Radiation Budget Archived 2006-09-01 at the Wayback Machine
- Greenhouse effect -Citizendium