The greenhouse effect is a good thing.

It warms the planet to its comfortable average of 59 degrees

Fahrenheit (15 degrees Celsius) and keeps life on earth, well, livable. Without it the world would be a frozen,

uninhabitable place, more like Mars. The problem is, mankind’s voracious burning of fossil fuels for energy is

artificially amping up the natural greenhouse effect. The result? An increase in global warming that is altering

the planet’s climate systems in countless ways. Here’s a look at what the greenhouse effect is, what causes it,

and how we can temper its contributions to our changing climate.

What Is the Greenhouse Effect?

Identified by scientists as far back as 1896, the greenhouse effect is the natural warming of the earth that

results when gases in the atmosphere trap heat from the sun that would otherwise escape into space.

What Causes the Greenhouse Effect?

Sunlight makes the earth habitable. While 30 percent of the solar energy that reaches our world is reflected

back to space, approximately 70 percent passes through the atmosphere to the earth’s surface, where it is

absorbed by the land, oceans, and atmosphere, and heats the planet. This heat is then radiated back up in the

form of invisible infrared light. While some of this infrared light continues on into space, the vast majority—

indeed, some 90 percent—gets absorbed by atmospheric gases, known as greenhouse gases, and redirected

back toward the earth, causing further warming.

For most of the past 800,000 years—much longer than human civilization has existed—the concentration of

greenhouse gases in our atmosphere was between about 200 and 280 parts per million. (In other words, there

were 200 to 280 molecules of the gases per million molecules of air.) But in the past century, that

concentration has jumped to more than 400 parts per million, driven up by human activities such as burning

fossil fuels and deforestation. The higher concentrations of greenhouse gases—and carbon dioxide in

particular—is causing extra heat to be trapped and global temperatures to rise

The Consequences of the Greenhouse Effect

Today’s human-caused greenhouse gas emissions are higher than ever, the concentration of greenhouse

gases in the atmosphere is rising rapidly, and according to the IPCC, the planet is heating up. Between

preindustrial times and now, the earth’s average temperature has increased 1.8 degrees Fahrenheit (1.0

degrees Celsius), with approximately two-thirds of that warming occurring in the last handful of decades alone.

According to the IPCC, 1983 to 2012 was likely the warmest 30-year period of the last 1,400 years (in the

Northern Hemisphere, where assessment is possible). And all five of the years from 2014 to 2018 were

the hottest on record globally. If warming trends continue at the current rate, it’s estimated global warming will

reach 2.7 degrees Fahrenheit (1.5 degrees Celsius) above preindustrial levels between 2030 and 2052.

Fueled by man-made greenhouse gas emissions, global warming is altering the earth’s climate systems in

many ways. It is:

 Causing more frequent and/or intense extreme weather events, including heat

waves, hurricanes, droughts, and floods.

 Exacerbating precipitation extremes, making wet regions wetter and dry regions drier.

 Raising sea levels due to melting glaciers and sea ice and an increase in ocean temperatures
(warmer water expands, which can contribute to sea level rise).

 Altering ecosystems and natural habitat, shifting the geographic ranges, seasonal activities,
migration patterns, and abundance of land, freshwater, and marine species.

These changes pose threats not only to plants and wildlife, but directly to people. Warmer temperatures mean

insects that spread diseases like dengue fever and Zika can thrive—and heat waves are getting hotter and

more lethal to humans. People could go hungry when our food supply is diminished thanks to droughts and

floods—a 2011 National Research Council study found that for every degree Celsius that the planet heats

up, crop yields will go down 5 to 15 percent. Food insecurity can lead to mass human migration and political

instability. And in January 2019, the Department of Defense released a report that described the threats to

U.S. military installations and operations around the world due to flooding, droughts, and other impacts of

climate change.
Greenhouse effect
The greenhouse effect 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.[1][2]

Radiatively active gases (i.e., greenhouse gases) in a planet's atmosphere radiate energy in all directions. Part
of this radiation is directed towards the surface, warming it.[3] The intensity of the downward radiation – that is,
the strength of the greenhouse effect – will depend on the atmosphere's temperature and on the amount of
greenhouse gases that the atmosphere contains.
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, however, mainly the burning of fossil fuels and clearcutting of forests,
have accelerated the greenhouse effect and caused global warming.[4]
The planet Venus experienced runaway greenhouse effect, resulting in an atmosphere which is 96% carbon
dioxide, with surface atmospheric pressure roughly the same as found 900 m (3,000 ft) 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 K (462 °C; 863 °F).[5][6][7]
The term "greenhouse effect" continues to see use in scientific circles and the media despite being a
slight misnomer, as an atmosphere reduces radiative heat loss[8] while a greenhouse blocks convective heat
loss.[2] The result, however, is an increase in temperature in both cases.[9][10]

History
Main article: History of climate change science

The existence of the greenhouse effect, while not named as such, was proposed by Joseph Fourier in 1824.
[11]
 The argument and the evidence were further strengthened by Claude Pouillet in 1827 and 1838. John
Tyndall was the first to measure the infrared absorption and emission of various gases and vapours. From
1859 onwards, he showed that the effect was due to a very small proportion of the atmosphere, with the main
gases having no effect, and was largely due to water vapour, though small percentages of hydrocarbons and
carbon dioxide had a significant effect.[12] The effect was more fully quantified by Svante Arrhenius in 1896,
who made the first quantitative prediction of global warming due to a hypothetical doubling of atmospheric
carbon dioxide.[13] 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 Nils Gustaf Ekholm in 1901.[14][15]
Earth receives energy from the Sun in the form of ultraviolet, visible, and near-infrared radiation. About 26% of
the incoming solar energy is reflected to space by the atmosphere and clouds, and 19% is absorbed by the
atmosphere and clouds. Most of the remaining energy is absorbed at the surface of Earth. Because the Earth's
surface is colder than the Sun, it radiates at wavelengths that are much longer than the wavelengths that were
absorbed. Most of this thermal radiation is absorbed by the atmosphere and warms it. The atmosphere also
gains heat by sensible and latent heat fluxes 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 equilibrium temperature than if the atmosphere did not radiate.
An ideal thermally conductive blackbody at the same distance from the Sun as Earth would have a
temperature of about 5.3 °C (41.5 °F). However, because Earth reflects about 30%[16][17] of the incoming
sunlight, this idealized planet's effective temperature (the temperature of a blackbody that would emit the same
amount of radiation) would be about −18 °C (0 °F).[18][19] The surface temperature of this hypothetical planet is
33 °C (59 °F) below Earth's actual surface temperature of approximately 14 °C (57 °F).[20] The greenhouse
effect is the contribution of greenhouse gases to this difference.[clarification needed]

Greenhouse gases
Main article: Greenhouse gas

By their percentage contribution to the greenhouse effect on Earth the four major gases are:[22][23]
 water vapor, 36–70%
 carbon dioxide, 9–26%
 methane, 4–9%
 ozone, 3–7%
It is not possible to assign a specific percentage to each gas because the absorption and emission bands of
the gases overlap (hence the ranges given above). Clouds also absorb and emit infrared radiation and thus
affect the radiative properties of the atmosphere.[23]

Role in climate change

Strengthening of the greenhouse effect through human activities is known as the enhanced (or anthropogenic)
greenhouse effect.[25] This increase in radiative forcing from human activity is attributable mainly to increased
atmospheric carbon dioxide levels.[26] According to the 2014 Assessment Report from the Intergovernmental
Panel on Climate Change, "atmospheric concentrations of carbon dioxide, methane and nitrous oxide are
unprecedented in at least the last 800,000 years. Their effects, together with those of other anthropogenic
drivers, have been detected throughout the climate system and are extremely likely to have been the dominant
cause of the observed warming since the mid-20th century'".[27]

CO
2 is produced by fossil fuel burning and other activities such as cement production and tropical deforestation.
[28]
 Measurements of CO
2 from the Mauna Loa observatory show that concentrations have increased from about 313 parts per million
(ppm)[29] in 1960, passing the 400 ppm milestone on May 9, 2013.[30] The current observed amount of CO
2 exceeds the geological record maxima (~300 ppm) from ice core data.[31] The effect of combustion-produced
carbon dioxide on the global climate, a special case of the greenhouse effect first described in 1896 by Svante
Arrhenius, has also been called the Callendar effect.
Over the past 800,000 years,[32] ice core data shows that carbon dioxide has varied from values as low as 180
ppm to the pre-industrial level of 270 ppm.[33] Paleoclimatologists consider variations in carbon dioxide
concentration to be a fundamental factor influencing climate variations over this time scale.[34][35]

Real greenhouses
The "greenhouse effect" of the atmosphere is named by analogy to greenhouses which become warmer in
sunlight. However, a greenhouse is not primarily warmed by the "greenhouse effect".[36] "Greenhouse effect" is
actually a misnomer since heating in the usual greenhouse is due to the reduction of convection,[10] while the
"greenhouse effect" works by preventing absorbed heat from leaving the structure through radiative transfer.
A greenhouse is built of any material that passes sunlight: usually glass or plastic. The sun warms the ground
and contents inside just like the outside, and these then warm the air. Outside, the warm air near the surface
rises and mixes with cooler air aloft, keeping the temperature lower than inside, where the air continues to heat
up because it is confined within the greenhouse. This can be demonstrated by opening a small window near
the roof of a greenhouse: the temperature will drop considerably. It was demonstrated experimentally (R. W.
Wood, 1909) that a (not heated) "greenhouse" with a cover of rock salt (which is transparent to infrared) heats
up an enclosure similarly to one with a glass cover.[9] Thus greenhouses work primarily by
preventing convective cooling.[8]
Heated greenhouses are yet another matter: as they have an internal source of heating, it is desirable to
minimise the amount of heat leaking out by radiative cooling. This can be done through the use of adequate
glazing.[37]

Related effects
Anti-greenhouse effect
See also: Anti-greenhouse effect

The anti-greenhouse effect is a mechanism similar and symmetrical to the greenhouse effect: in the
greenhouse effect, the atmosphere lets radiation in while not letting thermal radiation out, thus warming the
body surface; in the anti-greenhouse effect, the atmosphere keeps radiation out while letting thermal radiation
out, which lowers the equilibrium surface temperature. Such an effect has been proposed for Saturn's
moon Titan.[38]
Runaway greenhouse effect
See also: runaway greenhouse effect

A runaway greenhouse effect occurs if positive feedbacks lead to the evaporation of all greenhouse gases into
the atmosphere.[39] A runaway greenhouse effect involving carbon dioxide and water vapor has long ago been
hypothesized to have occurred on Venus,[40] this idea is still largely accepted [citation needed].

Bodies other than Earth

The 'greenhouse effect' on Venus is particularly large for several reasons:

1. It is nearer to the Sun than Earth by about 30%.

2. Its very dense atmosphere consists mainly of carbon dioxid
Greenhouse gas Chemical formula Global Warming Potential, Atmospheric
100-year time horizon (year

Carbon Dioxide CO2 1 100*

Methane CH4 25 12

Nitrous Oxide N2O 298 114

Chlorofluorocarbon-12 CCl2F2 10,900 100

(CFC-12)

Hydrofluorocarbon-23 CHF3 14,800 270

(HFC-23)

Sulfur Hexafluoride SF6 22,800 3,200

Nitrogen Trifluoride NF3 17,200 740

Sources and Concentrations of Major Greenhouse Gases

Greenhouse gas Major sources Pre-industrial 201

concentration (ppb) concentr
Greenhouse gas Chemical formula Global Warming Potential, Atmospheric
100-year time horizon (year

(ppb

Carbon Dioxide Fossil fuel combustion; Deforestation; 278,000 390,000 (in

Cement production

Methane Fossil fuel production; Agriculture; 722 1,803 (in 20

Landfills

Nitrous Oxide Fertilizer application; Fossil fuel and 271 324 (in 2011
biomass combustion; Industrial processes

Chlorofluorocarbon-12 Refrigerants 0 0.527

(CFC-12)

Hydrofluorocarbon-23 Refrigerants 0 0.024

(HFC-23)

Sulfur Hexafluoride Electricity transmission 0 0.0073

Nitrogen Trifluoride Semiconductor manufacturing 0 0.00086