Greenhouse gas

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A greenhouse gas (sometimes abbreviated GHG) is a gas that absorbs and emits radiant energy within the thermal infrared range. Greenhouse gas_sentence_0

Greenhouse gases cause the greenhouse effect on planets. Greenhouse gas_sentence_1

The primary greenhouse gases in Earth's atmosphere are water vapor (H 2O), carbon dioxide (CO 2), methane (CH 4), nitrous oxide (N 2O), and ozone (O3). Greenhouse gas_sentence_2

Without greenhouse gases, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F). Greenhouse gas_sentence_3

The atmospheres of Venus, Mars and Titan also contain greenhouse gases. Greenhouse gas_sentence_4

Human activities since the beginning of the Industrial Revolution (around 1750) have produced a 45% increase in the atmospheric concentration of carbon dioxide, from 280 ppm in 1750 to 415 ppm in 2019. Greenhouse gas_sentence_5

The last time the atmospheric concentration of carbon dioxide was this high was over 3 million years ago. Greenhouse gas_sentence_6

This increase has occurred despite the uptake of more than half of the emissions by various natural "sinks" involved in the carbon cycle. Greenhouse gas_sentence_7

The vast majority of anthropogenic carbon dioxide emissions come from combustion of fossil fuels, principally coal, petroleum (including oil) and natural gas, with additional contributions coming from deforestation and other changes in land use. Greenhouse gas_sentence_8

The leading source of anthropogenic methane emissions is agriculture, closely followed by gas venting and fugitive emissions from the fossil-fuel industry. Greenhouse gas_sentence_9

Traditional rice cultivation is the second biggest agricultural methane source after livestock, with a near-term warming impact equivalent to the carbon-dioxide emissions from all aviation. Greenhouse gas_sentence_10

At current emission rates, temperatures could increase by 2 °C (3.6 °F), which the United Nations' Intergovernmental Panel on Climate Change (IPCC) designated as the upper limit to avoid "dangerous" levels, by 2036. Greenhouse gas_sentence_11

Gases in Earth's atmosphere Greenhouse gas_section_0

Main articles: Greenhouse effect and Atmosphere of Earth Greenhouse gas_sentence_12

Non-greenhouse gases Greenhouse gas_section_1

The major constituents of Earth's atmosphere, nitrogen (N 2)(78%), oxygen (O 2)(21%), and argon (Ar)(0.9%), are not greenhouse gases because molecules containing two atoms of the same element such as N 2 and O 2 have no net change in the distribution of their electrical charges when they vibrate, and monatomic gases such as Ar do not have vibrational modes. Greenhouse gas_sentence_13

Hence they are almost totally unaffected by infrared radiation. Greenhouse gas_sentence_14

Some molecules containing just two atoms of different elements, such as carbon monoxide (CO) and hydrogen chloride (HCl), do absorb infrared radiation, but these molecules are short-lived in the atmosphere owing to their reactivity or solubility. Greenhouse gas_sentence_15

Therefore, they do not contribute significantly to the greenhouse effect and often are omitted when discussing greenhouse gases. Greenhouse gas_sentence_16

Greenhouse gases Greenhouse gas_section_2

See also: Global warming and Carbon dioxide in Earth's atmosphere Greenhouse gas_sentence_17

Greenhouse gases are those that absorb and emit infrared radiation in the wavelength range emitted by Earth. Greenhouse gas_sentence_18

Carbon dioxide (0.04%), nitrous oxide, methane and ozone are trace gases that account for almost 0.1% of Earth's atmosphere and have an appreciable greenhouse effect. Greenhouse gas_sentence_19

In order, the most abundant greenhouse gases in Earth's atmosphere are: Greenhouse gas_sentence_20

Greenhouse gas_unordered_list_0

Atmospheric concentrations are determined by the balance between sources (emissions of the gas from human activities and natural systems) and sinks (the removal of the gas from the atmosphere by conversion to a different chemical compound or absorption by bodies of water). Greenhouse gas_sentence_21

The proportion of an emission remaining in the atmosphere after a specified time is the "airborne fraction" (AF). Greenhouse gas_sentence_22

The annual airborne fraction is the ratio of the atmospheric increase in a given year to that year's total emissions. Greenhouse gas_sentence_23

As of 2006 the annual airborne fraction for CO 2 was about 0.45. Greenhouse gas_sentence_24

The annual airborne fraction increased at a rate of 0.25 ± 0.21% per year over the period 1959–2006. Greenhouse gas_sentence_25

Indirect radiative effects Greenhouse gas_section_3

Some gases have indirect radiative effects (whether or not they are greenhouse gases themselves). Greenhouse gas_sentence_26

This happens in two main ways. Greenhouse gas_sentence_27

One way is that when they break down in the atmosphere they produce another greenhouse gas. Greenhouse gas_sentence_28

For example, methane and carbon monoxide (CO) are oxidized to give carbon dioxide (and methane oxidation also produces water vapor). Greenhouse gas_sentence_29

Oxidation of CO to CO 2 directly produces an unambiguous increase in radiative forcing although the reason is subtle. Greenhouse gas_sentence_30

The peak of the thermal IR emission from Earth's surface is very close to a strong vibrational absorption band of CO 2 (wavelength 15 microns, or wavenumber 667 cm). Greenhouse gas_sentence_31

On the other hand, the single CO vibrational band only absorbs IR at much shorter wavelengths (4.7 microns, or 2145 cm), where the emission of radiant energy from Earth's surface is at least a factor of ten lower. Greenhouse gas_sentence_32

Oxidation of methane to CO 2, which requires reactions with the OH radical, produces an instantaneous reduction in radiative absorption and emission since CO 2 is a weaker greenhouse gas than methane. Greenhouse gas_sentence_33

However, the oxidations of CO and CH 4 are entwined since both consume OH radicals. Greenhouse gas_sentence_34

In any case, the calculation of the total radiative effect includes both direct and indirect forcing. Greenhouse gas_sentence_35

A second type of indirect effect happens when chemical reactions in the atmosphere involving these gases change the concentrations of greenhouse gases. Greenhouse gas_sentence_36

For example, the destruction of non-methane volatile organic compounds (NMVOCs) in the atmosphere can produce ozone. Greenhouse gas_sentence_37

The size of the indirect effect can depend strongly on where and when the gas is emitted. Greenhouse gas_sentence_38

Methane has indirect effects in addition to forming CO 2. Greenhouse gas_sentence_39

The main chemical that reacts with methane in the atmosphere is the hydroxyl radical (OH), thus more methane means that the concentration of OH goes down. Greenhouse gas_sentence_40

Effectively, methane increases its own atmospheric lifetime and therefore its overall radiative effect. Greenhouse gas_sentence_41

The oxidation of methane can produce both ozone and water; and is a major source of water vapor in the normally dry stratosphere. Greenhouse gas_sentence_42

CO and NMVOCs produce CO 2 when they are oxidized. Greenhouse gas_sentence_43

They remove OH from the atmosphere, and this leads to higher concentrations of methane. Greenhouse gas_sentence_44

The surprising effect of this is that the global warming potential of CO is three times that of CO 2. Greenhouse gas_sentence_45

The same process that converts NMVOCs to carbon dioxide can also lead to the formation of tropospheric ozone. Greenhouse gas_sentence_46

Halocarbons have an indirect effect because they destroy stratospheric ozone. Greenhouse gas_sentence_47

Finally, hydrogen can lead to ozone production and CH 4 increases as well as producing stratospheric water vapor. Greenhouse gas_sentence_48

Contribution of clouds to Earth's greenhouse effect Greenhouse gas_section_4

The major non-gas contributor to Earth's greenhouse effect, clouds, also absorb and emit infrared radiation and thus have an effect on greenhouse gas radiative properties. Greenhouse gas_sentence_49

Clouds are water droplets or ice crystals suspended in the atmosphere. Greenhouse gas_sentence_50

Impacts on the overall greenhouse effect Greenhouse gas_section_5

The contribution of each gas to the greenhouse effect is determined by the characteristics of that gas, its abundance, and any indirect effects it may cause. Greenhouse gas_sentence_51

For example, the direct radiative effect of a mass of methane is about 84 times stronger than the same mass of carbon dioxide over a 20-year time frame but it is present in much smaller concentrations so that its total direct radiative effect has so far been smaller, in part due to its shorter atmospheric lifetime in the absence of additional carbon sequestration. Greenhouse gas_sentence_52

On the other hand, in addition to its direct radiative impact, methane has a large, indirect radiative effect because it contributes to ozone formation. Greenhouse gas_sentence_53

Shindell et al. Greenhouse gas_sentence_54

(2005) argues that the contribution to climate change from methane is at least double previous estimates as a result of this effect. Greenhouse gas_sentence_55

When ranked by their direct contribution to the greenhouse effect, the most important are: Greenhouse gas_sentence_56

Greenhouse gas_table_general_0

CompoundGreenhouse gas_header_cell_0_0_0 FormulaGreenhouse gas_header_cell_0_0_1 Concentration in

atmosphere (ppm)Greenhouse gas_header_cell_0_0_2

Contribution
(%)Greenhouse gas_header_cell_0_0_3
Water vapor and cloudsGreenhouse gas_cell_0_1_0 H

2OGreenhouse gas_cell_0_1_1

10–50,000Greenhouse gas_cell_0_1_2 36–72%Greenhouse gas_cell_0_1_3
Carbon dioxideGreenhouse gas_cell_0_2_0 CO

2Greenhouse gas_cell_0_2_1

~400Greenhouse gas_cell_0_2_2 9–26%Greenhouse gas_cell_0_2_3
MethaneGreenhouse gas_cell_0_3_0 CH

4Greenhouse gas_cell_0_3_1

~1.8Greenhouse gas_cell_0_3_2 4–9%Greenhouse gas_cell_0_3_3
OzoneGreenhouse gas_cell_0_4_0 O

3Greenhouse gas_cell_0_4_1

2–8Greenhouse gas_cell_0_4_2 3–7%Greenhouse gas_cell_0_4_3
notes:
Water vapor strongly varies locally
The concentration in stratosphere. About 90% of the ozone in Earth's atmosphere is contained in the stratosphere.Greenhouse gas_header_cell_0_5_0

In addition to the main greenhouse gases listed above, other greenhouse gases include sulfur hexafluoride, hydrofluorocarbons and perfluorocarbons (see IPCC list of greenhouse gases). Greenhouse gas_sentence_57

Some greenhouse gases are not often listed. Greenhouse gas_sentence_58

For example, nitrogen trifluoride has a high global warming potential (GWP) but is only present in very small quantities. Greenhouse gas_sentence_59

Proportion of direct effects at a given moment Greenhouse gas_section_6

It is not possible to state that a certain gas causes an exact percentage of the greenhouse effect. Greenhouse gas_sentence_60

This is because some of the gases absorb and emit radiation at the same frequencies as others, so that the total greenhouse effect is not simply the sum of the influence of each gas. Greenhouse gas_sentence_61

The higher ends of the ranges quoted are for each gas alone; the lower ends account for overlaps with the other gases. Greenhouse gas_sentence_62

In addition, some gases, such as methane, are known to have large indirect effects that are still being quantified. Greenhouse gas_sentence_63

Atmospheric lifetime Greenhouse gas_section_7

The atmospheric lifetime of a species therefore measures the time required to restore equilibrium following a sudden increase or decrease in its concentration in the atmosphere. Greenhouse gas_sentence_64

Individual atoms or molecules may be lost or deposited to sinks such as the soil, the oceans and other waters, or vegetation and other biological systems, reducing the excess to background concentrations. Greenhouse gas_sentence_65

The average time taken to achieve this is the mean lifetime. Greenhouse gas_sentence_66

Carbon dioxide has a variable atmospheric lifetime, and cannot be specified precisely. Greenhouse gas_sentence_67

Although more than half of the CO 2 emitted is removed from the atmosphere within a century, some fraction (about 20%) of emitted CO 2 remains in the atmosphere for many thousands of years. Greenhouse gas_sentence_68

Similar issues apply to other greenhouse gases, many of which have longer mean lifetimes than CO 2, e.g. N2O has a mean atmospheric lifetime of 121 years. Greenhouse gas_sentence_69

Radiative forcing and annual greenhouse gas index Greenhouse gas_section_8

Earth absorbs some of the radiant energy received from the sun, reflects some of it as light and reflects or radiates the rest back to space as heat. Greenhouse gas_sentence_70

Earth's surface temperature depends on this balance between incoming and outgoing energy. Greenhouse gas_sentence_71

If this energy balance is shifted, Earth's surface becomes warmer or cooler, leading to a variety of changes in global climate. Greenhouse gas_sentence_72

A number of natural and man-made mechanisms can affect the global energy balance and force changes in Earth's climate. Greenhouse gas_sentence_73

Greenhouse gases are one such mechanism. Greenhouse gas_sentence_74

Greenhouse gases absorb and emit some of the outgoing energy radiated from Earth's surface, causing that heat to be retained in the lower atmosphere. Greenhouse gas_sentence_75

As explained above, some greenhouse gases remain in the atmosphere for decades or even centuries, and therefore can affect Earth's energy balance over a long period. Greenhouse gas_sentence_76

Radiative forcing quantifies (in Watts per square meter) the effect of factors that influence Earth's energy balance; including changes in the concentrations of greenhouse gases. Greenhouse gas_sentence_77

Positive radiative forcing leads to warming by increasing the net incoming energy, whereas negative radiative forcing leads to cooling. Greenhouse gas_sentence_78

The Annual Greenhouse Gas Index (AGGI) is defined by atmospheric scientists at NOAA as the ratio of total direct radiative forcing due to long-lived and well-mixed greenhouse gases for any year for which adequate global measurements exist, to that present in year 1990. Greenhouse gas_sentence_79

These radiative forcing levels are relative to those present in year 1750 (i.e. prior to the start of the industrial era). Greenhouse gas_sentence_80

1990 is chosen because it is the baseline year for the Kyoto Protocol, and is the publication year of the first IPCC Scientific Assessment of Climate Change. Greenhouse gas_sentence_81

As such, NOAA states that the AGGI "measures the commitment that (global) society has already made to living in a changing climate. Greenhouse gas_sentence_82

It is based on the highest quality atmospheric observations from sites around the world. Greenhouse gas_sentence_83

Its uncertainty is very low." Greenhouse gas_sentence_84

Global warming potential Greenhouse gas_section_9

The global warming potential (GWP) depends on both the efficiency of the molecule as a greenhouse gas and its atmospheric lifetime. Greenhouse gas_sentence_85

GWP is measured relative to the same mass of CO 2 and evaluated for a specific timescale. Greenhouse gas_sentence_86

Thus, if a gas has a high (positive) radiative forcing but also a short lifetime, it will have a large GWP on a 20-year scale but a small one on a 100-year scale. Greenhouse gas_sentence_87

Conversely, if a molecule has a longer atmospheric lifetime than CO 2 its GWP will increase when the timescale is considered. Greenhouse gas_sentence_88

Carbon dioxide is defined to have a GWP of 1 over all time periods. Greenhouse gas_sentence_89

Methane has an atmospheric lifetime of 12 ± 3 years. Greenhouse gas_sentence_90

The 2007 IPCC report lists the GWP as 72 over a time scale of 20 years, 25 over 100 years and 7.6 over 500 years. Greenhouse gas_sentence_91

A 2014 analysis, however, states that although methane's initial impact is about 100 times greater than that of CO 2, because of the shorter atmospheric lifetime, after six or seven decades, the impact of the two gases is about equal, and from then on methane's relative role continues to decline. Greenhouse gas_sentence_92

The decrease in GWP at longer times is because methane is degraded to water and CO 2 through chemical reactions in the atmosphere. Greenhouse gas_sentence_93

Examples of the atmospheric lifetime and GWP relative to CO 2 for several greenhouse gases are given in the following table: Greenhouse gas_sentence_94

Greenhouse gas_table_general_1

Atmospheric lifetime and GWP relative to CO 2 at different time horizon for various greenhouse gasesGreenhouse gas_table_caption_1
Gas nameGreenhouse gas_header_cell_1_0_0 Chemical
formulaGreenhouse gas_header_cell_1_0_1
Lifetime
(years)Greenhouse gas_header_cell_1_0_2
Global warming potential (GWP) for given time horizonGreenhouse gas_header_cell_1_0_3
20-yrGreenhouse gas_header_cell_1_1_0 100-yrGreenhouse gas_header_cell_1_1_1 500-yrGreenhouse gas_header_cell_1_1_2
Carbon dioxideGreenhouse gas_cell_1_2_0 CO

2Greenhouse gas_cell_1_2_1

Greenhouse gas_cell_1_2_2 1Greenhouse gas_cell_1_2_3 1Greenhouse gas_cell_1_2_4 1Greenhouse gas_cell_1_2_5
MethaneGreenhouse gas_cell_1_3_0 CH

4Greenhouse gas_cell_1_3_1

12Greenhouse gas_cell_1_3_2 84Greenhouse gas_cell_1_3_3 28Greenhouse gas_cell_1_3_4 7.6Greenhouse gas_cell_1_3_5
Nitrous oxideGreenhouse gas_cell_1_4_0 N

2OGreenhouse gas_cell_1_4_1

121Greenhouse gas_cell_1_4_2 264Greenhouse gas_cell_1_4_3 265Greenhouse gas_cell_1_4_4 153Greenhouse gas_cell_1_4_5
CFC-12Greenhouse gas_cell_1_5_0 CCl

2F 2Greenhouse gas_cell_1_5_1

100Greenhouse gas_cell_1_5_2 10 800Greenhouse gas_cell_1_5_3 10 200Greenhouse gas_cell_1_5_4 5 200Greenhouse gas_cell_1_5_5
HCFC-22Greenhouse gas_cell_1_6_0 CHClF

2Greenhouse gas_cell_1_6_1

12Greenhouse gas_cell_1_6_2 5 280Greenhouse gas_cell_1_6_3 1 760Greenhouse gas_cell_1_6_4 549Greenhouse gas_cell_1_6_5
TetrafluoromethaneGreenhouse gas_cell_1_7_0 CF

4Greenhouse gas_cell_1_7_1

50 000Greenhouse gas_cell_1_7_2 4 880Greenhouse gas_cell_1_7_3 6 630Greenhouse gas_cell_1_7_4 11 200Greenhouse gas_cell_1_7_5
HexafluoroethaneGreenhouse gas_cell_1_8_0 C

2F 6Greenhouse gas_cell_1_8_1

10 000Greenhouse gas_cell_1_8_2 8 210Greenhouse gas_cell_1_8_3 11 100Greenhouse gas_cell_1_8_4 18 200Greenhouse gas_cell_1_8_5
Sulfur hexafluorideGreenhouse gas_cell_1_9_0 SF

6Greenhouse gas_cell_1_9_1

3 200Greenhouse gas_cell_1_9_2 17 500Greenhouse gas_cell_1_9_3 23 500Greenhouse gas_cell_1_9_4 32 600Greenhouse gas_cell_1_9_5
Nitrogen trifluorideGreenhouse gas_cell_1_10_0 NF

3Greenhouse gas_cell_1_10_1

500Greenhouse gas_cell_1_10_2 12 800Greenhouse gas_cell_1_10_3 16 100Greenhouse gas_cell_1_10_4 20 700Greenhouse gas_cell_1_10_5
No single lifetime for atmospheric CO2 can be given.Greenhouse gas_header_cell_1_11_0

The use of CFC-12 (except some essential uses) has been phased out due to its ozone depleting properties. Greenhouse gas_sentence_95

The phasing-out of less active HCFC-compounds will be completed in 2030. Greenhouse gas_sentence_96

Natural and anthropogenic sources Greenhouse gas_section_10

Aside from purely human-produced synthetic halocarbons, most greenhouse gases have both natural and human-caused sources. Greenhouse gas_sentence_97

During the pre-industrial Holocene, concentrations of existing gases were roughly constant, because the large natural sources and sinks roughly balanced. Greenhouse gas_sentence_98

In the industrial era, human activities have added greenhouse gases to the atmosphere, mainly through the burning of fossil fuels and clearing of forests. Greenhouse gas_sentence_99

The 2007 Fourth Assessment Report compiled by the IPCC (AR4) noted that "changes in atmospheric concentrations of greenhouse gases and aerosols, land cover and solar radiation alter the energy balance of the climate system", and concluded that "increases in anthropogenic greenhouse gas concentrations is very likely to have caused most of the increases in global average temperatures since the mid-20th century". Greenhouse gas_sentence_100

In AR4, "most of" is defined as more than 50%. Greenhouse gas_sentence_101

Abbreviations used in the two tables below: ppm = parts-per-million; ppb = parts-per-billion; ppt = parts-per-trillion; W/m = watts per square metre Greenhouse gas_sentence_102

Greenhouse gas_table_general_2

Current greenhouse gas concentrationsGreenhouse gas_table_caption_2
GasGreenhouse gas_header_cell_2_0_0 Pre-1750

tropospheric concentrationGreenhouse gas_header_cell_2_0_1

Recent

tropospheric concentrationGreenhouse gas_header_cell_2_0_2

Absolute increase

since 1750Greenhouse gas_header_cell_2_0_3

Percentage

increase since 1750Greenhouse gas_header_cell_2_0_4

Increased

radiative forcing (W/m)Greenhouse gas_header_cell_2_0_5

Carbon dioxide (CO

2)Greenhouse gas_cell_2_1_0

280 ppmGreenhouse gas_cell_2_1_1 395.4 ppmGreenhouse gas_cell_2_1_2 115.4 ppmGreenhouse gas_cell_2_1_3 41.2%Greenhouse gas_cell_2_1_4 1.88Greenhouse gas_cell_2_1_5
Methane (CH

4)Greenhouse gas_cell_2_2_0

700 ppbGreenhouse gas_cell_2_2_1 1893 ppb /

1762 ppbGreenhouse gas_cell_2_2_2

1193 ppb /

1062 ppbGreenhouse gas_cell_2_2_3

170.4% /

151.7%Greenhouse gas_cell_2_2_4

0.49Greenhouse gas_cell_2_2_5
Nitrous oxide (N

2O)Greenhouse gas_cell_2_3_0

270 ppbGreenhouse gas_cell_2_3_1 326 ppb /

324 ppbGreenhouse gas_cell_2_3_2

56 ppb /

54 ppbGreenhouse gas_cell_2_3_3

20.7% /

20.0%Greenhouse gas_cell_2_3_4

0.17Greenhouse gas_cell_2_3_5
Tropospheric

ozone (O 3)Greenhouse gas_cell_2_4_0

237 ppbGreenhouse gas_cell_2_4_1 337 ppbGreenhouse gas_cell_2_4_2 100 ppbGreenhouse gas_cell_2_4_3 42%Greenhouse gas_cell_2_4_4 0.4Greenhouse gas_cell_2_4_5

Greenhouse gas_table_general_3

Relevant to radiative forcing and/or ozone depletion; all of the following have no natural sources and hence zero amounts pre-industrialGreenhouse gas_table_caption_3
GasGreenhouse gas_header_cell_3_0_0 Recent

tropospheric concentrationGreenhouse gas_header_cell_3_0_1

Increased

radiative forcing (W/m)Greenhouse gas_header_cell_3_0_2

CFC-11

(trichlorofluoromethane) (CCl 3F)Greenhouse gas_cell_3_1_0

236 ppt /

234 pptGreenhouse gas_cell_3_1_1

0.061Greenhouse gas_cell_3_1_2
CFC-12 (CCl

2F 2)Greenhouse gas_cell_3_2_0

527 ppt /

527 pptGreenhouse gas_cell_3_2_1

0.169Greenhouse gas_cell_3_2_2
CFC-113 (Cl

2FC-CClF 2)Greenhouse gas_cell_3_3_0

74 ppt /

74 pptGreenhouse gas_cell_3_3_1

0.022Greenhouse gas_cell_3_3_2
HCFC-22 (CHClF

2)Greenhouse gas_cell_3_4_0

231 ppt /

210 pptGreenhouse gas_cell_3_4_1

0.046Greenhouse gas_cell_3_4_2
HCFC-141b (CH

3CCl 2F)Greenhouse gas_cell_3_5_0

24 ppt /

21 pptGreenhouse gas_cell_3_5_1

0.0036Greenhouse gas_cell_3_5_2
HCFC-142b (CH

3CClF 2)Greenhouse gas_cell_3_6_0

23 ppt /

21 pptGreenhouse gas_cell_3_6_1

0.0042Greenhouse gas_cell_3_6_2
Halon 1211 (CBrClF

2)Greenhouse gas_cell_3_7_0

4.1 ppt /

4.0 pptGreenhouse gas_cell_3_7_1

0.0012Greenhouse gas_cell_3_7_2
Halon 1301 (CBrClF

3)Greenhouse gas_cell_3_8_0

3.3 ppt /

3.3 pptGreenhouse gas_cell_3_8_1

0.001Greenhouse gas_cell_3_8_2
HFC-134a (CH

2FCF 3)Greenhouse gas_cell_3_9_0

75 ppt /

64 pptGreenhouse gas_cell_3_9_1

0.0108Greenhouse gas_cell_3_9_2
Carbon tetrachloride (CCl

4)Greenhouse gas_cell_3_10_0

85 ppt /

83 pptGreenhouse gas_cell_3_10_1

0.0143Greenhouse gas_cell_3_10_2
Sulfur hexafluoride (SF

6)Greenhouse gas_cell_3_11_0

7.79 ppt /

7.39 pptGreenhouse gas_cell_3_11_1

0.0043Greenhouse gas_cell_3_11_2
Other halocarbonsGreenhouse gas_cell_3_12_0 Varies by

substanceGreenhouse gas_cell_3_12_1

collectively

0.02Greenhouse gas_cell_3_12_2

Halocarbons in totalGreenhouse gas_cell_3_13_0 Greenhouse gas_cell_3_13_1 0.3574Greenhouse gas_cell_3_13_2

Ice cores provide evidence for greenhouse gas concentration variations over the past 800,000 years (see the following section). Greenhouse gas_sentence_103

Both CO 2 and CH 4 vary between glacial and interglacial phases, and concentrations of these gases correlate strongly with temperature. Greenhouse gas_sentence_104

Direct data does not exist for periods earlier than those represented in the ice core record, a record that indicates CO 2 mole fractions stayed within a range of 180 ppm to 280 ppm throughout the last 800,000 years, until the increase of the last 250 years. Greenhouse gas_sentence_105

However, various proxies and modeling suggests larger variations in past epochs; 500 million years ago CO 2 levels were likely 10 times higher than now. Greenhouse gas_sentence_106

Indeed, higher CO 2 concentrations are thought to have prevailed throughout most of the Phanerozoic eon, with concentrations four to six times current concentrations during the Mesozoic era, and ten to fifteen times current concentrations during the early Palaeozoic era until the middle of the Devonian period, about 400 Ma. Greenhouse gas_sentence_107

The spread of land plants is thought to have reduced CO 2 concentrations during the late Devonian, and plant activities as both sources and sinks of CO 2 have since been important in providing stabilising feedbacks. Greenhouse gas_sentence_108

Earlier still, a 200-million year period of intermittent, widespread glaciation extending close to the equator (Snowball Earth) appears to have been ended suddenly, about 550 Ma, by a colossal volcanic outgassing that raised the CO 2 concentration of the atmosphere abruptly to 12%, about 350 times modern levels, causing extreme greenhouse conditions and carbonate deposition as limestone at the rate of about 1 mm per day. Greenhouse gas_sentence_109

This episode marked the close of the Precambrian eon, and was succeeded by the generally warmer conditions of the Phanerozoic, during which multicellular animal and plant life evolved. Greenhouse gas_sentence_110

No volcanic carbon dioxide emission of comparable scale has occurred since. Greenhouse gas_sentence_111

In the modern era, emissions to the atmosphere from volcanoes are approximately 0.645 billion tonnes of CO 2 per year, whereas humans contribute 29 billion tonnes of CO 2 each year. Greenhouse gas_sentence_112

Ice cores Greenhouse gas_section_11

Measurements from Antarctic ice cores show that before industrial emissions started atmospheric CO 2 mole fractions were about 280 parts per million (ppm), and stayed between 260 and 280 during the preceding ten thousand years. Greenhouse gas_sentence_113

Carbon dioxide mole fractions in the atmosphere have gone up by approximately 35 percent since the 1900s, rising from 280 parts per million by volume to 387 parts per million in 2009. Greenhouse gas_sentence_114

One study using evidence from stomata of fossilized leaves suggests greater variability, with carbon dioxide mole fractions above 300 ppm during the period seven to ten thousand years ago, though others have argued that these findings more likely reflect calibration or contamination problems rather than actual CO 2 variability. Greenhouse gas_sentence_115

Because of the way air is trapped in ice (pores in the ice close off slowly to form bubbles deep within the firn) and the time period represented in each ice sample analyzed, these figures represent averages of atmospheric concentrations of up to a few centuries rather than annual or decadal levels. Greenhouse gas_sentence_116

Changes since the Industrial Revolution Greenhouse gas_section_12

Since the beginning of the Industrial Revolution, the concentrations of many of the greenhouse gases have increased. Greenhouse gas_sentence_117

For example, the mole fraction of carbon dioxide has increased from 280 ppm to 415 ppm, or 120 ppm over modern pre-industrial levels. Greenhouse gas_sentence_118

The first 30 ppm increase took place in about 200 years, from the start of the Industrial Revolution to 1958; however the next 90 ppm increase took place within 56 years, from 1958 to 2014. Greenhouse gas_sentence_119

Recent data also shows that the concentration is increasing at a higher rate. Greenhouse gas_sentence_120

In the 1960s, the average annual increase was only 37% of what it was in 2000 through 2007. Greenhouse gas_sentence_121

Total cumulative emissions from 1870 to 2017 were 425±20 GtC (1539 GtCO2) from fossil fuels and industry, and 180±60 GtC (660 GtCO2) from land use change. Greenhouse gas_sentence_122

Land-use change, such as deforestation, caused about 31% of cumulative emissions over 1870–2017, coal 32%, oil 25%, and gas 10%. Greenhouse gas_sentence_123

Today, the stock of carbon in the atmosphere increases by more than 3 million tonnes per annum (0.04%) compared with the existing stock. Greenhouse gas_sentence_124

This increase is the result of human activities by burning fossil fuels, deforestation and forest degradation in tropical and boreal regions. Greenhouse gas_sentence_125

The other greenhouse gases produced from human activity show similar increases in both amount and rate of increase. Greenhouse gas_sentence_126

Many observations are available online in a variety of Atmospheric Chemistry Observational Databases. Greenhouse gas_sentence_127

Role of water vapor Greenhouse gas_section_13

Water vapor accounts for the largest percentage of the greenhouse effect, between 36% and 66% for clear sky conditions and between 66% and 85% when including clouds. Greenhouse gas_sentence_128

Water vapor concentrations fluctuate regionally, but human activity does not directly affect water vapor concentrations except at local scales, such as near irrigated fields. Greenhouse gas_sentence_129

Indirectly, human activity that increases global temperatures will increase water vapor concentrations, a process known as water vapor feedback. Greenhouse gas_sentence_130

The atmospheric concentration of vapor is highly variable and depends largely on temperature, from less than 0.01% in extremely cold regions up to 3% by mass in saturated air at about 32 °C. Greenhouse gas_sentence_131

(See Relative humidity#Other important facts.) Greenhouse gas_sentence_132

The average residence time of a water molecule in the atmosphere is only about nine days, compared to years or centuries for other greenhouse gases such as CH 4 and CO 2. Greenhouse gas_sentence_133

Water vapor responds to and amplifies effects of the other greenhouse gases. Greenhouse gas_sentence_134

The Clausius–Clapeyron relation establishes that more water vapor will be present per unit volume at elevated temperatures. Greenhouse gas_sentence_135

This and other basic principles indicate that warming associated with increased concentrations of the other greenhouse gases also will increase the concentration of water vapor (assuming that the relative humidity remains approximately constant; modeling and observational studies find that this is indeed so). Greenhouse gas_sentence_136

Because water vapor is a greenhouse gas, this results in further warming and so is a "positive feedback" that amplifies the original warming. Greenhouse gas_sentence_137

Eventually other earth processes offset these positive feedbacks, stabilizing the global temperature at a new equilibrium and preventing the loss of Earth's water through a Venus-like runaway greenhouse effect. Greenhouse gas_sentence_138

Anthropogenic greenhouse gases Greenhouse gas_section_14

See also: Climate change and ecosystems Greenhouse gas_sentence_139

Since about 1750 human activity has increased the concentration of carbon dioxide and other greenhouse gases. Greenhouse gas_sentence_140

Measured atmospheric concentrations of carbon dioxide are currently 100 ppm higher than pre-industrial levels. Greenhouse gas_sentence_141

Natural sources of carbon dioxide are more than 20 times greater than sources due to human activity, but over periods longer than a few years natural sources are closely balanced by natural sinks, mainly photosynthesis of carbon compounds by plants and marine plankton. Greenhouse gas_sentence_142

As a result of this balance, the atmospheric mole fraction of carbon dioxide remained between 260 and 280 parts per million for the 10,000 years between the end of the last glacial maximum and the start of the industrial era. Greenhouse gas_sentence_143

It is likely that anthropogenic (i.e., human-induced) warming, such as that due to elevated greenhouse gas levels, has had a discernible influence on many physical and biological systems. Greenhouse gas_sentence_144

Future warming is projected to have a range of impacts, including sea level rise, increased frequencies and severities of some extreme weather events, loss of biodiversity, and regional changes in agricultural productivity. Greenhouse gas_sentence_145

The main sources of greenhouse gases due to human activity are: Greenhouse gas_sentence_146

Greenhouse gas_unordered_list_1

  • burning of fossil fuels and deforestation leading to higher carbon dioxide concentrations in the air. Land use change (mainly deforestation in the tropics) account for up to one third of total anthropogenic CO 2 emissions.Greenhouse gas_item_1_7
  • livestock enteric fermentation and manure management, paddy rice farming, land use and wetland changes, man-made lakes, pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane.Greenhouse gas_item_1_8
  • use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes.Greenhouse gas_item_1_9
  • agricultural activities, including the use of fertilizers, that lead to higher nitrous oxide (N 2O) concentrations.Greenhouse gas_item_1_10

The seven sources of CO 2 from fossil fuel combustion are (with percentage contributions for 2000–2004): Greenhouse gas_sentence_147

This list needs updating, as it uses an out of date source. Greenhouse gas_sentence_148

Greenhouse gas_unordered_list_2

  • Liquid fuels (e.g., gasoline, fuel oil): 36%Greenhouse gas_item_2_11
  • Solid fuels (e.g., coal): 35%Greenhouse gas_item_2_12
  • Gaseous fuels (e.g., natural gas): 20%Greenhouse gas_item_2_13
  • Cement production:3 %Greenhouse gas_item_2_14
  • Flaring gas industrially and at wells: 1%Greenhouse gas_item_2_15
  • Non-fuel hydrocarbons:1%Greenhouse gas_item_2_16
  • "International bunker fuels" of transport not included in national inventories: 4 %Greenhouse gas_item_2_17

Carbon dioxide, methane, nitrous oxide (N 2O) and three groups of fluorinated gases (sulfur hexafluoride (SF 6), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs)) are the major anthropogenic greenhouse gases, and are regulated under the Kyoto Protocol international treaty, which came into force in 2005. Greenhouse gas_sentence_149

Emissions limitations specified in the Kyoto Protocol expired in 2012. Greenhouse gas_sentence_150

The Cancún agreement, agreed on in 2010, includes voluntary pledges made by 76 countries to control emissions. Greenhouse gas_sentence_151

At the time of the agreement, these 76 countries were collectively responsible for 85% of annual global emissions. Greenhouse gas_sentence_152

Although CFCs are greenhouse gases, they are regulated by the Montreal Protocol, which was motivated by CFCs' contribution to ozone depletion rather than by their contribution to global warming. Greenhouse gas_sentence_153

Note that ozone depletion has only a minor role in greenhouse warming, though the two processes often are confused in the media. Greenhouse gas_sentence_154

On 15 October 2016, negotiators from over 170 nations meeting at the summit of the United Nations Environment Programme reached a legally binding accord to phase out hydrofluorocarbons (HFCs) in an amendment to the Montreal Protocol. Greenhouse gas_sentence_155

Greenhouse gases emissions by sector Greenhouse gas_section_15

Global greenhouse gas emissions can be attributed to different sectors of the economy. Greenhouse gas_sentence_156

This provides a picture of the varying contributions of different types of economic activity to global warming, and helps in understanding the changes required to mitigate climate change. Greenhouse gas_sentence_157

Manmade greenhouse gas emissions can be divided into those that arise from the combustion of fuels to produce energy, and those generated by other processes. Greenhouse gas_sentence_158

Around two thirds of greenhouse gas emissions arise from the combustion of fuels. Greenhouse gas_sentence_159

Energy may be produced at the point of consumption, or by a generator for consumption by others. Greenhouse gas_sentence_160

Thus emissions arising from energy production may be categorised according to where they are emitted, or where the resulting energy is consumed. Greenhouse gas_sentence_161

If emissions are attributed at the point of production, then electricity generators contribute about 25% of global greenhouse gas emissions. Greenhouse gas_sentence_162

If these emissions are attributed to the final consumer then 24% of total emissions arise from manufacturing and construction, 17% from transportation, 11% from domestic consumers, and 7% from commercial consumers. Greenhouse gas_sentence_163

Around 4% of emissions arise from the energy consumed by the energy and fuel industry itself. Greenhouse gas_sentence_164

The remaining third of emissions arise from processes other than energy production. Greenhouse gas_sentence_165

12% of total emissions arise from agriculture, 7% from land use change and forestry, 6% from industrial processes, and 3% from waste. Greenhouse gas_sentence_166

Around 6% of emissions are fugitive emissions, which are waste gases released by the extraction of fossil fuels. Greenhouse gas_sentence_167

Electricity generation Greenhouse gas_section_16

See also: Life-cycle greenhouse-gas emissions of energy sources Greenhouse gas_sentence_168

Electricity generation emits over a quarter of global greenhouse gases. Greenhouse gas_sentence_169

Coal-fired power stations are the single largest emitter, with over 10 Gt CO 2 in 2018. Greenhouse gas_sentence_170

Although much less polluting than coal plants, natural gas-fired power plants are also major emitters. Greenhouse gas_sentence_171

Tourism Greenhouse gas_section_17

According to UNEP, global tourism is closely linked to climate change. Greenhouse gas_sentence_172

Tourism is a significant contributor to the increasing concentrations of greenhouse gases in the atmosphere. Greenhouse gas_sentence_173

Tourism accounts for about 50% of traffic movements. Greenhouse gas_sentence_174

Rapidly expanding air traffic contributes about 2.5% of the production of CO 2. Greenhouse gas_sentence_175

The number of international travelers is expected to increase from 594 million in 1996 to 1.6 billion by 2020, adding greatly to the problem unless steps are taken to reduce emissions. Greenhouse gas_sentence_176

Trucking and haulage Greenhouse gas_section_18

The trucking and haulage industry plays a part in production of CO 2, contributing around 20% of the UK's total carbon emissions a year, with only the energy industry having a larger impact at around 39%. Greenhouse gas_sentence_177

Average carbon emissions within the haulage industry are falling—in the thirty-year period from 1977 to 2007, the carbon emissions associated with a 200-mile journey fell by 21 percent; NOx emissions are also down 87 percent, whereas journey times have fallen by around a third. Greenhouse gas_sentence_178

Plastic Greenhouse gas_section_19

Plastic is produced mainly from fossil fuels. Greenhouse gas_sentence_179

Plastic manufacturing is estimated to use 8 percent of yearly global oil production. Greenhouse gas_sentence_180

The EPA estimates as many as five mass units of carbon dioxide are emitted for each mass unit of polyethylene terephthalate (PET) produced—the type of plastic most commonly used for beverage bottles, the transportation produce greenhouse gases also. Greenhouse gas_sentence_181

Plastic waste emits carbon dioxide when it degrades. Greenhouse gas_sentence_182

In 2018 research claimed that some of the most common plastics in the environment release the greenhouse gases methane and ethylene when exposed to sunlight in an amount that can affect the earth climate. Greenhouse gas_sentence_183

From the other side, if it is placed in a landfill, it becomes a carbon sink although biodegradable plastics have caused methane emissions. Greenhouse gas_sentence_184

Due to the lightness of plastic versus glass or metal, plastic may reduce energy consumption. Greenhouse gas_sentence_185

For example, packaging beverages in PET plastic rather than glass or metal is estimated to save 52% in transportation energy, if the glass or metal package is single-use, of course. Greenhouse gas_sentence_186

In 2019 a new report "Plastic and Climate" was published. Greenhouse gas_sentence_187

According to the report plastic will contribute greenhouse gases in the equivalent of 850 million tonnes of carbon dioxide (CO2) to the atmosphere in 2019. Greenhouse gas_sentence_188

In current trend, annual emissions will grow to 1.34 billion tonnes by 2030. Greenhouse gas_sentence_189

By 2050 plastic could emit 56 billion tonnes of Greenhouse gas emissions, as much as 14 percent of the Earth's remaining carbon budget. Greenhouse gas_sentence_190

The report says that only solutions which involve a reduction in consumption can solve the problem, while others like biodegradable plastic, ocean cleanup, using renewable energy in plastic industry can do little, and in some cases may even worsen it. Greenhouse gas_sentence_191

Pharmaceutical industry Greenhouse gas_section_20

The pharmaceutical industry emitted 52 megatonnes of carbon dioxide into the atmosphere in 2015. Greenhouse gas_sentence_192

This is more than the automotive sector. Greenhouse gas_sentence_193

However this analysis used the combined emissions of conglomerates which produce pharmaceuticals as well as other products. Greenhouse gas_sentence_194

Aviation Greenhouse gas_section_21

Approximately 3.5% of the overall human impact on climate are from the aviation sector. Greenhouse gas_sentence_195

The impact of the sector on climate in the late 20 years had doubled, but the part of the contribution of the sector in comparison to other sectors did not change because other sectors grew as well. Greenhouse gas_sentence_196

Digital sector Greenhouse gas_section_22

In 2017 the digital sector produced 3.3% of global GHG emissions, above civil aviation (2%). Greenhouse gas_sentence_197

In 2020 this is expected to reach 4%, the equivalent emissions of India in 2015. Greenhouse gas_sentence_198

Sanitation sector Greenhouse gas_section_23

Wastewater as well as sanitation systems are known to contribute to greenhouse-gas emissions (GHG) mainly through the breakdown of excreta during the treatment process. Greenhouse gas_sentence_199

This results in the generation of methane gas, that is then released into the environment. Greenhouse gas_sentence_200

Emissions from the sanitation and wastewater sector have been focused mainly on treatment systems, particularly treatment plants, and this accounts for the bulk of the carbon footprint for the sector. Greenhouse gas_sentence_201

In as much as climate impacts from wastewater and sanitation systems present global risks, low-income countries experience greater risks in many cases. Greenhouse gas_sentence_202

In recent years, attention to adaptation needs within the sanitation sector is just beginning to gain momentum. Greenhouse gas_sentence_203

Regional and national attribution of emissions Greenhouse gas_section_24

See also: Kyoto Protocol and government action Greenhouse gas_sentence_204

According to the Environmental Protection Agency (EPA), GHG emissions in the United States can be traced from different sectors. Greenhouse gas_sentence_205

There are several ways of measuring greenhouse gas emissions, for example, see World Bank (2010) for tables of national emissions data. Greenhouse gas_sentence_206

Some variables that have been reported include: Greenhouse gas_sentence_207

Greenhouse gas_unordered_list_3

  • Definition of measurement boundaries: Emissions can be attributed geographically, to the area where they were emitted (the territory principle) or by the activity principle to the territory produced the emissions. These two principles result in different totals when measuring, for example, electricity importation from one country to another, or emissions at an international airport.Greenhouse gas_item_3_18
  • Time horizon of different gases: Contribution of a given greenhouse gas is reported as a CO 2 equivalent. The calculation to determine this takes into account how long that gas remains in the atmosphere. This is not always known accurately and calculations must be regularly updated to reflect new information.Greenhouse gas_item_3_19
  • What sectors are included in the calculation (e.g., energy industries, industrial processes, agriculture etc.): There is often a conflict between transparency and availability of data.Greenhouse gas_item_3_20
  • The measurement protocol itself: This may be via direct measurement or estimation. The four main methods are the emission factor-based method, mass balance method, predictive emissions monitoring systems, and continuous emissions monitoring systems. These methods differ in accuracy, cost, and usability.Greenhouse gas_item_3_21

These measures are sometimes used by countries to assert various policy/ethical positions on climate change (Banuri et al., 1996, p. 94). Greenhouse gas_sentence_208

The use of different measures leads to a lack of comparability, which is problematic when monitoring progress towards targets. Greenhouse gas_sentence_209

There are arguments for the adoption of a common measurement tool, or at least the development of communication between different tools. Greenhouse gas_sentence_210

Emissions may be measured over long time periods. Greenhouse gas_sentence_211

This measurement type is called historical or cumulative emissions. Greenhouse gas_sentence_212

Cumulative emissions give some indication of who is responsible for the build-up in the atmospheric concentration of greenhouse gases (IEA, 2007, p. 199). Greenhouse gas_sentence_213

The national accounts balance would be positively related to carbon emissions. Greenhouse gas_sentence_214

The national accounts balance shows the difference between exports and imports. Greenhouse gas_sentence_215

For many richer nations, such as the United States, the accounts balance is negative because more goods are imported than they are exported. Greenhouse gas_sentence_216

This is mostly due to the fact that it is cheaper to produce goods outside of developed countries, leading the economies of developed countries to become increasingly dependent on services and not goods. Greenhouse gas_sentence_217

We believed that a positive accounts balance would means that more production was occurring in a country, so more factories working would increase carbon emission levels. Greenhouse gas_sentence_218

Emissions may also be measured across shorter time periods. Greenhouse gas_sentence_219

Emissions changes may, for example, be measured against a base year of 1990. Greenhouse gas_sentence_220

1990 was used in the United Nations Framework Convention on Climate Change (UNFCCC) as the base year for emissions, and is also used in the Kyoto Protocol (some gases are also measured from the year 1995). Greenhouse gas_sentence_221

A country's emissions may also be reported as a proportion of global emissions for a particular year. Greenhouse gas_sentence_222

Another measurement is of per capita emissions. Greenhouse gas_sentence_223

This divides a country's total annual emissions by its mid-year population. Greenhouse gas_sentence_224

Per capita emissions may be based on historical or annual emissions (Banuri et al., 1996, pp. 106–07). Greenhouse gas_sentence_225

While cities are sometimes considered to be disproportionate contributors to emissions, per-capita emissions tend to be lower for cities than the averages in their countries. Greenhouse gas_sentence_226

From land-use change Greenhouse gas_section_25

Land-use change, e.g., the clearing of forests for agricultural use, can affect the concentration of greenhouse gases in the atmosphere by altering how much carbon flows out of the atmosphere into carbon sinks. Greenhouse gas_sentence_227

Accounting for land-use change can be understood as an attempt to measure "net" emissions, i.e., gross emissions from all sources minus the removal of emissions from the atmosphere by carbon sinks (Banuri et al., 1996, pp. 92–93). Greenhouse gas_sentence_228

There are substantial uncertainties in the measurement of net carbon emissions. Greenhouse gas_sentence_229

Additionally, there is controversy over how carbon sinks should be allocated between different regions and over time (Banuri et al., 1996, p. 93). Greenhouse gas_sentence_230

For instance, concentrating on more recent changes in carbon sinks is likely to favour those regions that have deforested earlier, e.g., Europe. Greenhouse gas_sentence_231

Greenhouse gas intensity Greenhouse gas_section_26

Greenhouse gas intensity is a ratio between greenhouse gas emissions and another metric, e.g., gross domestic product (GDP) or energy use. Greenhouse gas_sentence_232

The terms "carbon intensity" and "emissions intensity" are also sometimes used. Greenhouse gas_sentence_233

Emission intensities may be calculated using market exchange rates (MER) or purchasing power parity (PPP) (Banuri et al., 1996, p. 96). Greenhouse gas_sentence_234

Calculations based on MER show large differences in intensities between developed and developing countries, whereas calculations based on PPP show smaller differences. Greenhouse gas_sentence_235

Cumulative and historical emissions Greenhouse gas_section_27

Cumulative anthropogenic (i.e., human-emitted) emissions of CO 2 from fossil fuel use are a major cause of global warming, and give some indication of which countries have contributed most to human-induced climate change. Greenhouse gas_sentence_236

Overall, developed countries accounted for 83.8% of industrial CO 2 emissions over this time period, and 67.8% of total CO 2 emissions. Greenhouse gas_sentence_237

Developing countries accounted for industrial CO 2 emissions of 16.2% over this time period, and 32.2% of total CO 2 emissions. Greenhouse gas_sentence_238

The estimate of total CO 2 emissions includes biotic carbon emissions, mainly from deforestation. Greenhouse gas_sentence_239

Banuri et al. Greenhouse gas_sentence_240

(1996, p. 94) calculated per capita cumulative emissions based on then-current population. Greenhouse gas_sentence_241

The ratio in per capita emissions between industrialized countries and developing countries was estimated at more than 10 to 1. Greenhouse gas_sentence_242

Including biotic emissions brings about the same controversy mentioned earlier regarding carbon sinks and land-use change (Banuri et al., 1996, pp. 93–94). Greenhouse gas_sentence_243

The actual calculation of net emissions is very complex, and is affected by how carbon sinks are allocated between regions and the dynamics of the climate system. Greenhouse gas_sentence_244

Non-OECD countries accounted for 42% of cumulative energy-related CO 2 emissions between 1890 and 2007. Greenhouse gas_sentence_245

Over this time period, the US accounted for 28% of emissions; the EU, 23%; Russia, 11%; China, 9%; other OECD countries, 5%; Japan, 4%; India, 3%; and the rest of the world, 18%. Greenhouse gas_sentence_246

Changes since a particular base year Greenhouse gas_section_28

See also: Kyoto Protocol § Government action and emissions Greenhouse gas_sentence_247

Between 1970 and 2004, global growth in annual CO 2 emissions was driven by North America, Asia, and the Middle East. Greenhouse gas_sentence_248

The sharp acceleration in CO 2 emissions since 2000 to more than a 3% increase per year (more than 2 ppm per year) from 1.1% per year during the 1990s is attributable to the lapse of formerly declining trends in carbon intensity of both developing and developed nations. Greenhouse gas_sentence_249

China was responsible for most of global growth in emissions during this period. Greenhouse gas_sentence_250

Localised plummeting emissions associated with the collapse of the Soviet Union have been followed by slow emissions growth in this region due to more efficient energy use, made necessary by the increasing proportion of it that is exported. Greenhouse gas_sentence_251

In comparison, methane has not increased appreciably, and N 2O by 0.25% y. Greenhouse gas_sentence_252

Using different base years for measuring emissions has an effect on estimates of national contributions to global warming. Greenhouse gas_sentence_253

This can be calculated by dividing a country's highest contribution to global warming starting from a particular base year, by that country's minimum contribution to global warming starting from a particular base year. Greenhouse gas_sentence_254

Choosing between base years of 1750, 1900, 1950, and 1990 has a significant effect for most countries. Greenhouse gas_sentence_255

Within the G8 group of countries, it is most significant for the UK, France and Germany. Greenhouse gas_sentence_256

These countries have a long history of CO 2 emissions (see the section on Cumulative and historical emissions). Greenhouse gas_sentence_257

Annual emissions Greenhouse gas_section_29

Annual per capita emissions in the industrialized countries are typically as much as ten times the average in developing countries. Greenhouse gas_sentence_258

Due to China's fast economic development, its annual per capita emissions are quickly approaching the levels of those in the Annex I group of the Kyoto Protocol (i.e., the developed countries excluding the US). Greenhouse gas_sentence_259

Other countries with fast growing emissions are South Korea, Iran, and Australia (which apart from the oil rich Persian Gulf states, now has the highest per capita emission rate in the world). Greenhouse gas_sentence_260

On the other hand, annual per capita emissions of the EU-15 and the US are gradually decreasing over time. Greenhouse gas_sentence_261

Emissions in Russia and Ukraine have decreased fastest since 1990 due to economic restructuring in these countries. Greenhouse gas_sentence_262

Energy statistics for fast growing economies are less accurate than those for the industrialized countries. Greenhouse gas_sentence_263

For China's annual emissions in 2008, the Netherlands Environmental Assessment Agency estimated an uncertainty range of about 10%. Greenhouse gas_sentence_264

The greenhouse gas footprint refers to the emissions resulting from the creation of products or services. Greenhouse gas_sentence_265

It is more comprehensive than the commonly used carbon footprint, which measures only carbon dioxide, one of many greenhouse gases. Greenhouse gas_sentence_266

2015 was the first year to see both total global economic growth and a reduction of carbon emissions. Greenhouse gas_sentence_267

Top emitter countries Greenhouse gas_section_30

See also: List of countries by carbon dioxide emissions, List of countries by carbon dioxide emissions per capita, List of countries by greenhouse gas emissions, and List of countries by greenhouse gas emissions per capita Greenhouse gas_sentence_268

Annual Greenhouse gas_section_31

In 2009, the annual top ten emitting countries accounted for about two-thirds of the world's annual energy-related CO 2 emissions. Greenhouse gas_sentence_269

Greenhouse gas_table_general_4

Top-10 annual CO 2 emitters for the year 2017Greenhouse gas_table_caption_4
CountryGreenhouse gas_header_cell_4_0_0 % of global total
annual emissionsGreenhouse gas_header_cell_4_0_1
Total 2017 CO2 Emissions (kilotons)Greenhouse gas_header_cell_4_0_2 Tonnes of GHG
per capitaGreenhouse gas_header_cell_4_0_3
ChinaGreenhouse gas_cell_4_1_0 29.3Greenhouse gas_cell_4_1_1 10,877,217Greenhouse gas_cell_4_1_2 7.7Greenhouse gas_cell_4_1_3
United StatesGreenhouse gas_cell_4_2_0 13.8Greenhouse gas_cell_4_2_1 5,107,393Greenhouse gas_cell_4_2_2 15.7Greenhouse gas_cell_4_2_3
IndiaGreenhouse gas_cell_4_3_0 6.6Greenhouse gas_cell_4_3_1 2,454,773Greenhouse gas_cell_4_3_2 1.8Greenhouse gas_cell_4_3_3
RussiaGreenhouse gas_cell_4_4_0 4.8Greenhouse gas_cell_4_4_1 1,764,865Greenhouse gas_cell_4_4_2 12.2Greenhouse gas_cell_4_4_3
JapanGreenhouse gas_cell_4_5_0 3.6Greenhouse gas_cell_4_5_1 1,320,776Greenhouse gas_cell_4_5_2 10.4Greenhouse gas_cell_4_5_3
GermanyGreenhouse gas_cell_4_6_0 2.1Greenhouse gas_cell_4_6_1 796,528Greenhouse gas_cell_4_6_2 9.7Greenhouse gas_cell_4_6_3
South KoreaGreenhouse gas_cell_4_7_0 1.8Greenhouse gas_cell_4_7_1 673,323Greenhouse gas_cell_4_7_2 13.2Greenhouse gas_cell_4_7_3
IranGreenhouse gas_cell_4_8_0 1.8Greenhouse gas_cell_4_8_1 671,450Greenhouse gas_cell_4_8_2 8.2Greenhouse gas_cell_4_8_3
Saudi ArabiaGreenhouse gas_cell_4_9_0 1.7Greenhouse gas_cell_4_9_1 638,761Greenhouse gas_cell_4_9_2 19.3Greenhouse gas_cell_4_9_3
CanadaGreenhouse gas_cell_4_10_0 1.7Greenhouse gas_cell_4_10_1 617,300Greenhouse gas_cell_4_10_2 16.9Greenhouse gas_cell_4_10_3

Embedded emissions Greenhouse gas_section_32

One way of attributing greenhouse gas emissions is to measure the embedded emissions (also referred to as "embodied emissions") of goods that are being consumed. Greenhouse gas_sentence_270

Emissions are usually measured according to production, rather than consumption. Greenhouse gas_sentence_271

For example, in the main international treaty on climate change (the UNFCCC), countries report on emissions produced within their borders, e.g., the emissions produced from burning fossil fuels. Greenhouse gas_sentence_272

Under a production-based accounting of emissions, embedded emissions on imported goods are attributed to the exporting, rather than the importing, country. Greenhouse gas_sentence_273

Under a consumption-based accounting of emissions, embedded emissions on imported goods are attributed to the importing country, rather than the exporting, country. Greenhouse gas_sentence_274

Davis and Caldeira (2010) found that a substantial proportion of CO 2 emissions are traded internationally. Greenhouse gas_sentence_275

The net effect of trade was to export emissions from China and other emerging markets to consumers in the US, Japan, and Western Europe. Greenhouse gas_sentence_276

Based on annual emissions data from the year 2004, and on a per-capita consumption basis, the top-5 emitting countries were found to be (in tCO 2 per person, per year): Luxembourg (34.7), the US (22.0), Singapore (20.2), Australia (16.7), and Canada (16.6). Greenhouse gas_sentence_277

Carbon Trust research revealed that approximately 25% of all CO 2 emissions from human activities 'flow' (i.e., are imported or exported) from one country to another. Greenhouse gas_sentence_278

Major developed economies were found to be typically net importers of embodied carbon emissions—with UK consumption emissions 34% higher than production emissions, and Germany (29%), Japan (19%) and the US (13%) also significant net importers of embodied emissions. Greenhouse gas_sentence_279

Effect of policy Greenhouse gas_section_33

Governments have taken action to reduce greenhouse gas emissions to mitigate climate change. Greenhouse gas_sentence_280

Assessments of policy effectiveness have included work by the Intergovernmental Panel on Climate Change, International Energy Agency, and United Nations Environment Programme. Greenhouse gas_sentence_281

Policies implemented by governments have included national and regional targets to reduce emissions, promoting energy efficiency, and support for a renewable energy transition such as Solar energy as an effective use of renewable energy because solar uses energy from the sun and does not release pollutants into the air. Greenhouse gas_sentence_282

Countries and regions listed in Annex I of the United Nations Framework Convention on Climate Change (UNFCCC) (i.e., the OECD and former planned economies of the Soviet Union) are required to submit periodic assessments to the UNFCCC of actions they are taking to address climate change. Greenhouse gas_sentence_283

Analysis by the UNFCCC (2011) suggested that policies and measures undertaken by Annex I Parties may have produced emission savings of 1.5 thousand Tg CO 2-eq in the year 2010, with most savings made in the energy sector. Greenhouse gas_sentence_284

The projected emissions saving of 1.5 thousand Tg CO 2-eq is measured against a hypothetical "baseline" of Annex I emissions, i.e., projected Annex I emissions in the absence of policies and measures. Greenhouse gas_sentence_285

The total projected Annex I saving of 1.5 thousand CO 2-eq does not include emissions savings in seven of the Annex I Parties. Greenhouse gas_sentence_286

Projections Greenhouse gas_section_34

Further information: climate change scenario § Quantitative emissions projections Greenhouse gas_sentence_287

See also: Global climate model § Projections of future climate change Greenhouse gas_sentence_288

A wide range of projections of future emissions have been produced. Greenhouse gas_sentence_289

Rogner et al. Greenhouse gas_sentence_290

(2007) assessed the scientific literature on greenhouse gas projections. Greenhouse gas_sentence_291

Rogner et al. Greenhouse gas_sentence_292

(2007) concluded that unless energy policies changed substantially, the world would continue to depend on fossil fuels until 2025–2030. Greenhouse gas_sentence_293

Projections suggest that more than 80% of the world's energy will come from fossil fuels. Greenhouse gas_sentence_294

This conclusion was based on "much evidence" and "high agreement" in the literature. Greenhouse gas_sentence_295

Projected annual energy-related CO 2 emissions in 2030 were 40–110% higher than in 2000, with two-thirds of the increase originating in developing countries. Greenhouse gas_sentence_296

Projected annual per capita emissions in developed country regions remained substantially lower (2.8–5.1 tonnes CO 2) than those in developed country regions (9.6–15.1 tonnes CO 2). Greenhouse gas_sentence_297

Projections consistently showed increase in annual world emissions of "Kyoto" gases, measured in CO 2-equivalent) of 25–90% by 2030, compared to 2000. Greenhouse gas_sentence_298

Relative CO2 emission from various fuels Greenhouse gas_section_35

One liter of gasoline, when used as a fuel, produces 2.32 kg (about 1300 liters or 1.3 cubic meters) of carbon dioxide, a greenhouse gas. Greenhouse gas_sentence_299

One US gallon produces 19.4 lb (1,291.5 gallons or 172.65 cubic feet). Greenhouse gas_sentence_300

Greenhouse gas_table_general_5

Mass of carbon dioxide emitted per quantity of energy for various fuelsGreenhouse gas_table_caption_5
Fuel nameGreenhouse gas_header_cell_5_0_0 CO

2

emitted 
(lbs/10 Btu)Greenhouse gas_header_cell_5_0_1
CO

2

emitted 
(g/MJ)Greenhouse gas_header_cell_5_0_2
CO

2

emitted 
(g/kWh)Greenhouse gas_header_cell_5_0_3
Natural gasGreenhouse gas_cell_5_1_0 117Greenhouse gas_cell_5_1_1 50.30Greenhouse gas_cell_5_1_2 181.08Greenhouse gas_cell_5_1_3
Liquefied petroleum gasGreenhouse gas_cell_5_2_0 139Greenhouse gas_cell_5_2_1 59.76Greenhouse gas_cell_5_2_2 215.14Greenhouse gas_cell_5_2_3
PropaneGreenhouse gas_cell_5_3_0 139Greenhouse gas_cell_5_3_1 59.76Greenhouse gas_cell_5_3_2 215.14Greenhouse gas_cell_5_3_3
Aviation gasolineGreenhouse gas_cell_5_4_0 153Greenhouse gas_cell_5_4_1 65.78Greenhouse gas_cell_5_4_2 236.81Greenhouse gas_cell_5_4_3
Automobile gasolineGreenhouse gas_cell_5_5_0 156Greenhouse gas_cell_5_5_1 67.07Greenhouse gas_cell_5_5_2 241.45Greenhouse gas_cell_5_5_3
KeroseneGreenhouse gas_cell_5_6_0 159Greenhouse gas_cell_5_6_1 68.36Greenhouse gas_cell_5_6_2 246.10Greenhouse gas_cell_5_6_3
Fuel oilGreenhouse gas_cell_5_7_0 161Greenhouse gas_cell_5_7_1 69.22Greenhouse gas_cell_5_7_2 249.19Greenhouse gas_cell_5_7_3
Tires/tire derived fuelGreenhouse gas_cell_5_8_0 189Greenhouse gas_cell_5_8_1 81.26Greenhouse gas_cell_5_8_2 292.54Greenhouse gas_cell_5_8_3
Wood and wood wasteGreenhouse gas_cell_5_9_0 195Greenhouse gas_cell_5_9_1 83.83Greenhouse gas_cell_5_9_2 301.79Greenhouse gas_cell_5_9_3
Coal (bituminous)Greenhouse gas_cell_5_10_0 205Greenhouse gas_cell_5_10_1 88.13Greenhouse gas_cell_5_10_2 317.27Greenhouse gas_cell_5_10_3
Coal (sub-bituminous)Greenhouse gas_cell_5_11_0 213Greenhouse gas_cell_5_11_1 91.57Greenhouse gas_cell_5_11_2 329.65Greenhouse gas_cell_5_11_3
Coal (lignite)Greenhouse gas_cell_5_12_0 215Greenhouse gas_cell_5_12_1 92.43Greenhouse gas_cell_5_12_2 332.75Greenhouse gas_cell_5_12_3
Petroleum cokeGreenhouse gas_cell_5_13_0 225Greenhouse gas_cell_5_13_1 96.73Greenhouse gas_cell_5_13_2 348.23Greenhouse gas_cell_5_13_3
Tar-sand bitumenGreenhouse gas_cell_5_14_0 Greenhouse gas_cell_5_14_1 Greenhouse gas_cell_5_14_2 Greenhouse gas_cell_5_14_3
Greenhouse gas_cell_5_15_0 227Greenhouse gas_cell_5_15_1 97.59Greenhouse gas_cell_5_15_2 351.32Greenhouse gas_cell_5_15_3

Life-cycle greenhouse-gas emissions of energy sources Greenhouse gas_section_36

Main article: Life-cycle greenhouse gas emissions of energy sources Greenhouse gas_sentence_301

A 2011 IPCC report included a literature review of numerous energy sources' total life cycle CO 2 emissions. Greenhouse gas_sentence_302

Below are the CO 2 emission values that fell at the 50th percentile of all studies surveyed. Greenhouse gas_sentence_303

Greenhouse gas_table_general_6

Lifecycle greenhouse gas emissions by electricity source.Greenhouse gas_table_caption_6
TechnologyGreenhouse gas_header_cell_6_0_0 DescriptionGreenhouse gas_header_cell_6_0_1 50th percentile
(g CO

2/kWhe)Greenhouse gas_header_cell_6_0_2

HydroelectricGreenhouse gas_cell_6_1_0 reservoirGreenhouse gas_cell_6_1_1 4Greenhouse gas_cell_6_1_2
Ocean energyGreenhouse gas_cell_6_2_0 wave and tidalGreenhouse gas_cell_6_2_1 8Greenhouse gas_cell_6_2_2
WindGreenhouse gas_cell_6_3_0 onshoreGreenhouse gas_cell_6_3_1 12Greenhouse gas_cell_6_3_2
NuclearGreenhouse gas_cell_6_4_0 various generation II reactor typesGreenhouse gas_cell_6_4_1 16Greenhouse gas_cell_6_4_2
BiomassGreenhouse gas_cell_6_5_0 variousGreenhouse gas_cell_6_5_1 18Greenhouse gas_cell_6_5_2
Solar thermalGreenhouse gas_cell_6_6_0 parabolic troughGreenhouse gas_cell_6_6_1 22Greenhouse gas_cell_6_6_2
GeothermalGreenhouse gas_cell_6_7_0 hot dry rockGreenhouse gas_cell_6_7_1 45Greenhouse gas_cell_6_7_2
Solar photovoltaicGreenhouse gas_cell_6_8_0 Polycrystalline siliconGreenhouse gas_cell_6_8_1 46Greenhouse gas_cell_6_8_2
Natural gasGreenhouse gas_cell_6_9_0 various combined cycle turbines without scrubbingGreenhouse gas_cell_6_9_1 469Greenhouse gas_cell_6_9_2
CoalGreenhouse gas_cell_6_10_0 various generator types without scrubbingGreenhouse gas_cell_6_10_1 1001Greenhouse gas_cell_6_10_2

Removal from the atmosphere Greenhouse gas_section_37

Natural processes Greenhouse gas_section_38

Greenhouse gases can be removed from the atmosphere by various processes, as a consequence of: Greenhouse gas_sentence_304

Greenhouse gas_unordered_list_4

  • a physical change (condensation and precipitation remove water vapor from the atmosphere).Greenhouse gas_item_4_22
  • a chemical reaction within the atmosphere. For example, methane is oxidized by reaction with naturally occurring hydroxyl radical, OH· and degraded to CO 2 and water vapor (CO 2 from the oxidation of methane is not included in the methane Global warming potential). Other chemical reactions include solution and solid phase chemistry occurring in atmospheric aerosols.Greenhouse gas_item_4_23
  • a physical exchange between the atmosphere and the other components of the planet. An example is the mixing of atmospheric gases into the oceans.Greenhouse gas_item_4_24
  • a chemical change at the interface between the atmosphere and the other components of the planet. This is the case for CO 2, which is reduced by photosynthesis of plants, and which, after dissolving in the oceans, reacts to form carbonic acid and bicarbonate and carbonate ions (see ocean acidification).Greenhouse gas_item_4_25
  • a photochemical change. Halocarbons are dissociated by UV light releasing Cl· and F· as free radicals in the stratosphere with harmful effects on ozone (halocarbons are generally too stable to disappear by chemical reaction in the atmosphere).Greenhouse gas_item_4_26

Negative emissions Greenhouse gas_section_39

Main article: Carbon dioxide removal Greenhouse gas_sentence_305

A number of technologies remove greenhouse gases emissions from the atmosphere. Greenhouse gas_sentence_306

Most widely analysed are those that remove carbon dioxide from the atmosphere, either to geologic formations such as bio-energy with carbon capture and storage and carbon dioxide air capture, or to the soil as in the case with biochar. Greenhouse gas_sentence_307

The IPCC has pointed out that many long-term climate scenario models require large-scale man-made negative emissions to avoid serious climate change. Greenhouse gas_sentence_308

History of scientific research Greenhouse gas_section_40

In the late 19th century scientists experimentally discovered that N 2 and O 2 do not absorb infrared radiation (called, at that time, "dark radiation"), while water (both as true vapor and condensed in the form of microscopic droplets suspended in clouds) and CO 2 and other poly-atomic gaseous molecules do absorb infrared radiation. Greenhouse gas_sentence_309

In the early 20th century researchers realized that greenhouse gases in the atmosphere made Earth's overall temperature higher than it would be without them. Greenhouse gas_sentence_310

During the late 20th century, a scientific consensus evolved that increasing concentrations of greenhouse gases in the atmosphere cause a substantial rise in global temperatures and changes to other parts of the climate system, with consequences for the environment and for human health. Greenhouse gas_sentence_311

See also Greenhouse gas_section_41

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Greenhouse gas.