{"id":1310,"date":"2021-07-09T14:40:36","date_gmt":"2021-07-09T09:10:36","guid":{"rendered":"https:\/\/www.diabetesasia.org\/magazine\/?p=1310"},"modified":"2025-03-20T10:32:31","modified_gmt":"2025-03-20T05:02:31","slug":"greenhouse-effect","status":"publish","type":"post","link":"https:\/\/www.diabetesasia.org\/magazine\/greenhouse-effect\/","title":{"rendered":"Greenhouse effect"},"content":{"rendered":"

Greenhouse effect<\/h1>\n
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Greenhouse (disambiguation)<\/a>.<\/div>\n
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Greenhouse gases allow sunlight to pass through the atmosphere but then absorb and reflect the infrared radiation (heat) the planet emits<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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Quantitative analysis:<\/b>\u00a0Energy flows between space, the atmosphere, and Earth’s surface, with greenhouse gases in the atmosphere capturing a substantial portion of the heat reflected from the earth’s surface.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

The\u00a0greenhouse effect<\/b> is the process by which radiation from a planet’s atmosphere warms the planet’s surface to a temperature above what it would be without this atmosphere.<\/sup><\/p>\n

Radiatively active gases (i.e.,\u00a0greenhouse gases<\/a>) in a planet’s atmosphere radiate energy in all directions. Part of this radiation is directed towards the surface, thus warming it. The intensity of downward radiation \u2013 that is, the strength of the greenhouse effect \u2013 depends on the number of greenhouse gases that the atmosphere contains. The temperature rises until the intensity of upward radiation from the surface, thus cooling it, balances the downward energy flow.<\/p>\n

Earth’s natural greenhouse effect is critical to supporting life and initially was a precursor to life moving out of the ocean onto land. Human activities, mainly the burning of fossil fuels and clearcutting of forests, have increased the greenhouse effect and caused\u00a0global warming.<\/p>\n

The planet Venus\u00a0experienced a\u00a0runaway greenhouse effect, resulting in an atmosphere of 96% carbon dioxide\u00a0and a surface\u00a0atmospheric pressure roughly the same as found 900\u00a0m (3,000\u00a0ft) underwater on Earth. Venus may have had water oceans, but they would have boiled off as the mean surface temperature rose to the current 735\u00a0K (462\u00a0\u00b0C; 863\u00a0\u00b0F).<\/sup><\/p>\n

The term\u00a0greenhouse effect<\/i>\u00a0is a slight\u00a0misnomer because physical greenhouses warm via a different mechanism. The greenhouse effect as an atmospheric mechanism functions through\u00a0radiative heat loss,<\/sup>\u00a0while a traditional\u00a0greenhouse\u00a0as a built structure blocks\u00a0convective heat loss<\/a>. The result, however, is an increase in temperature in both cases.<\/p>\n

History<\/span><\/h2>\n
Main article:\u00a0History of climate change science<\/a><\/div>\n

The existence of the greenhouse effect, while not named as such, was proposed by\u00a0Joseph Fourier<\/a> in 1824. Claude Pouillet further strengthened the argument and the evidence\u00a0in 1827 and 1838.\u00a0John Tyndall<\/a> was the first to measure the infrared absorption and emission of various gases and vapors. From 1859 onwards, he showed that the effect was due to a tiny proportion of the atmosphere, with the main gases not affect, and was largely due to water vapor. However, small percentages of hydrocarbons and carbon dioxide had a significant effect. The effect was more fully quantified by\u00a0Svante Arrhenius in 1896, who made the first quantitative prediction of global warming due to a hypothetical doubling of atmospheric carbon dioxide. However, the term “greenhouse” was not used to refer to this effect by any of these scientists; the term was first used in this way by\u00a0Nils Gustaf Ekholm<\/a> in 1901.<\/sup><\/p>\n

Description<\/span><\/h2>\n
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The\u00a0solar radiation\u00a0spectrum for direct light at both the top of Earth’s atmosphere and at sea level<\/p>\n<\/div>\n<\/div>\n<\/div>\n

Earth receives energy from the Sun in the form of\u00a0ultraviolet,\u00a0visible, and\u00a0near-infrared radiation. About 26% of the incoming solar energy is reflected by the atmosphere and clouds, and 19% is absorbed by the atmosphere and clouds. Most of the remaining energy is absorbed in the surface of Earth. Because the Earth’s surface is colder\u00a0than the Sun, it radiates at\u00a0wavelengths much longer than the absorbed wavelengths. Most of this thermal radiation is absorbed by the atmosphere and warms it. The atmosphere also gains heat by\u00a0sensible\u00a0and\u00a0latent heat\u00a0fluxes from the surface. The atmosphere radiates energy both upwards and downwards; the part radiated downwards is absorbed by the surface of Earth. This leads to a higher\u00a0equilibrium temperature\u00a0than if the atmosphere did not radiate.<\/p>\n

An ideal thermally conductive\u00a0blackbody at the same distance from the Sun as Earth would have a temperature of about 5.3\u00a0\u00b0C (41.5\u00a0\u00b0F). However, because Earth reflects about 30%\u00a0of the incoming sunlight, this idealized planet’s\u00a0effective temperature (the temperature of a blackbody that would emit the same amount of radiation) would be about \u221218\u00a0\u00b0C (0\u00a0\u00b0F).\u00a0The surface temperature of this hypothetical planet is 33\u00a0\u00b0C (59\u00a0\u00b0F) below Earth’s actual surface temperature of approximately 14\u00a0\u00b0C (57\u00a0\u00b0F).\u00a0The greenhouse effect is the contribution of greenhouse gases to this difference.<\/p>\n

Details<\/span><\/h2>\n

The\u00a0idealized greenhouse model<\/a> is a simplification. In reality, the atmosphere near the Earth’s surface is largely opaque to thermal radiation, and most heat loss from the surface is by\u00a0convection<\/a>. However, radiative energy losses become increasingly important in the atmosphere, largely because of the decreasing concentration of water vapor, an important greenhouse gas. Rather than the surface itself, it is more realistic to think of the greenhouse effect as applying to a layer in the mid-troposphere<\/a>, which is effectively coupled to the surface by a\u00a0lapse rate<\/a>. A simple picture also assumes a steady state, but the diurnal cycle<\/a> and the seasonal cycle, and weather disturbances complicate matters in the real world. Solar heating applies only during the daytime. During the night, the atmosphere cools somewhat, but not great, because its emissivity<\/a>\u00a0is low.\u00a0Diurnal temperature changes<\/a>\u00a0decrease with height in the atmosphere.<\/p>\n

Within the region where radiative effects are important, the description given by the idealized greenhouse model becomes realistic. Earth’s surface, warmed to an “effective temperature” around \u221218 \u00b0C (0 \u00b0F), radiates long-wavelength\u00a0infrared<\/a> heat in the range of 4\u2013100 \u03bcm. At these wavelengths, greenhouse gases that were largely transparent to incoming solar radiation are more absorbent. Each layer of the atmosphere with greenhouse gases absorbs some of the heat radiated upwards from lower layers. It reradiates in all directions, both upwards and downwards, in equilibrium (by definition) the same amount as it has absorbed. This results in more warmth below. Increasing the concentration of the gases increases the amount of absorption and re-radiation and thereby further warms the layers and ultimately the surface below.<\/p>\n

Greenhouse gases\u2014including most diatomic gases with two different atoms (such as carbon monoxide, CO) and all gases with three or more atoms\u2014can absorb and emit infrared radiation. Though more than 99% of the dry atmosphere is IR transparent (because the main constituents\u2014N
\n2<\/sub><\/span>,\u00a0O
\n2<\/sub><\/span>, and Ar\u2014can not directly absorb or emit infrared radiation), intermolecular collisions cause the energy absorbed and emitted by the greenhouse gases to be shared with the other, non-IR-active gases.<\/p>\n

Greenhouse gases<\/span><\/h2>\n
Main article:\u00a0Greenhouse gas<\/a><\/div>\n

By their percentage contribution to the greenhouse effect on Earth, the four major gases are:[23]<\/a><\/sup>[24]<\/a><\/sup><\/p>\n

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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. Carbon dioxide is not as strong a greenhouse gas as water vapor. Still, it absorbs energy in longer wavelengths (12\u201315 micrometers) that water vapor does not, partially closing the “window” through which heat radiated by the surface would normally escape to space. (Illustration NASA, Robert Rohde)<\/p>\n<\/div>\n<\/div>\n<\/div>\n