Greenhouse Gases In The Atmosphere

Greenhouse gases in the atmosphere

Recent increases in atmospheric CO2. The monthly CO2 measurements display small seasonal oscillations in an overall yearly uptrend; each year's maximum is reached during the northern hemisphere's late spring, and declines during the northern hemisphere growing season as plants remove some CO2 from the atmosphere. Main article: Greenhouse effect The greenhouse effect was discovered by Joseph Fourier in 1824 and was first investigated quantitatively by Svante Arrhenius in 1896. It is the process by which emission of infrared radiation by atmospheric gases warms a planet's surface. On Earth, the major natural greenhouse gases are water vapor, which causes about 36-70% of the greenhouse effect (not including clouds); carbon dioxide, which causes 9-26%; methane, which causes 4-9%, and ozone, which causes 3-7%. The atmospheric concentrations of CO2 and methane (CH4) have increased by 31% and 149% respectively above pre-industrial levels since 1750. This is considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores. From less direct geological evidence it is believed that CO2 values this high were last attained 20 million years ago.[13] About three-quarters of the anthropogenic (man-made) emissions of CO2 to the atmosphere during the past 20 years are due to fossil fuel burning. The rest of the anthropogenic emissions are predominantly due to land-use change, especially deforestation.[14]

Changes in carbon dioxide during the Phanerozoic (the last 542 million years). The recent period is located on the left-hand side of the plot, and shows how high levels of CO2 have been sequestered in the form of hydrocarbons (e.g., coal, oil, natural gas) now being re-released in the combustion of fossil fuels.

Anthropogenic emission of greenhouse gases broken down by sector for the year 2000. Future CO2 levels are expected to rise due to ongoing burning of fossil fuels and land-use change. The rate of rise will depend on uncertain economic, sociological, technological, natural developments, but may be ultimately limited by the availability of fossil fuels. The IPCC Special Report on Emissions Scenarios gives a wide range of future CO2 scenarios,[15] ranging from 541 to 970 parts per million by the year 2100. Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100, if coal, tar sands or methane clathrates are extensively used.[citation needed] Carbon dioxide sink ecosystems (forests and oceans)[16] are being degraded by pollutants.[17] Degradation of major carbon sinks results in higher atmospheric CO2 levels. Positive feedback effects such as the expected release of methane from the melting of permafrost peat bogs in Siberia (possibly up to 70,000 million tonnes) may lead to significant additional sources of greenhouse gas emissions[18] not included in IPCC's climate models.[19] The measure of the temperature response to increased greenhouse gas concentrations and other anthropogenic and natural climate forcings is climate sensitivity. It is found by observational and model studies.[20] This sensitivity is usually expressed in terms of the temperature response expected from a doubling of CO2 in the atmosphere. The current literature estimates sensitivity in the range of 1.5 to 4.5 °C (2.7 to 8.1 °F).

Attributed and expected effects Main article: Effects of global warming

Global glacial mass balance in the last 50 years, reported to the WGMS and the NSIDC. The increased downward trend in the late 1980s is symptomatic of the increased rate and number of retreating glaciers. Some effects on both the natural environment and human life are, at least in part, already being attributed to global warming. A 2001 report by the IPCC suggests that glacier retreat, ice shelf disruption such as the Larsen Ice Shelf, sea level rise, changes in rainfall patterns, increased intensity and frequency of extreme weather events, are being attributed at least in part to global warming.[28] While changes are expected for overall patterns, intensity, and frequencies, it is difficult or impossible to attribute specific events (such as Hurricane Katrina) to global warming. Some anticipated effects include sea level rise of 110 to 770 mm (0.36 to 2.5 feet) by 2100,[29] repercussions to agriculture, possible slowing of the thermohaline circulation, reductions in the ozone layer, increased intensity and frequency of hurricanes and extreme weather events, lowering of ocean pH, and the spread of diseases such as malaria and dengue fever. One study predicts 18 to 35 percent of a sample of 1,103 animal and plant species would be extinct by 2050, based on future climate projections.[30] Mechanistic studies have documented extinctions due to recent climate change: McLaughlin et al. documented two populations of Bay checkerspot butterfly being threatened by precipitation change.[31] Parmesan states, "Few studies have been conducted at a scale that encompasses an entire species"[32] and McLaughlin et al. agree "few mechanistic studies have linked extinctions to recent climate change."[31] Two British scientists supporting the mainstream scientific opinion on global warming criticize what they call the "catastrophism and the 'Hollywoodisation'" of some of the expected effects. They argue the sensationalized claims cannot be justified by the science.[33] The extent and probability of these consequences has caused controversy, as is a matter of uncertainty. A summary of probable effects and recent understanding can be found in the report of the IPCC Working Group II;[28] the newer AR4 summary reports, "There is observational evidence for an increase of intense tropical cyclone activity in the North Atlantic since about 1970, correlated with increases of tropical sea surface temperatures.

There are also suggestions of increased intense tropical cyclone activity in some other regions where concerns over data quality are greater. Multi-decadal variability and the quality of the tropical cyclone records prior to routine satellite observations in about 1970 complicate the detection of long-term trends in tropical cyclone activity. There is no clear trend in the annual numbers of tropical cyclones."[1]

Other related issues Ocean acidification Main article: Ocean acidification Increased atmospheric CO2 increases the amount of CO2 dissolved in the oceans.[38] Carbon dioxide gas dissolved in the ocean reacts with water to form carbonic acid resulting in ocean acidification. Since biosystems are adapted to a narrow range of pH, this is a serious concern directly driven by increased atmospheric CO2 and not global warming.

Relationship to ozone depletion Main article: Ozone depletion Although they are often interlinked in the mass media, the connection between global warming and ozone depletion is not strong. There are four areas of linkage: •

The same CO2 radiative forcing that produces near-surface global warming is expected (perhaps surprisingly) to cool the stratosphere. This cooling, in turn, is expected to produce a relative increase in ozone (O3) depletion and the frequency of ozone holes.

Radiative forcing from various greenhouse gases and other sources

•

Conversely, ozone depletion represents a radiative forcing of the climate system. There are two opposing effects: Reduced ozone causes the stratosphere to absorb less solar radiation, thus cooling the stratosphere while warming the troposphere; the resulting colder stratosphere emits less long-wave radiation downward, thus cooling the troposphere. Overall, the cooling dominates; the IPCC concludes that "observed stratospheric O3 losses over the past two decades have caused a negative forcing of the surface-troposphere system"[39] of about −0.15 ± 0.10 watts per square meter (W/m2).[40]

•

One of the strongest predictions of the greenhouse effect theory is that the stratosphere will cool. Although this cooling has been observed, it is not trivial to separate the effects of changes in the concentration of greenhouse gases and ozone depletion since both will lead to cooling. However, this can be done by numerical stratospheric modeling. Results from the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory show that above 20 km (12.4 miles), the greenhouse gases dominate the cooling.[41]

•

Ozone depleting chemicals are also greenhouse gases, representing 0.34 ± 0.03 W/m2, or about 14% of the total radiative forcing from well-mixed greenhouse gases.[40]

Relationship to global dimming Main article: Global dimming Scientists have stated with 66-90% confidence that the effects of volcanic and humancaused aerosols have offset some of global warming, and that greenhouse gases would have resulted in more warming than observed if not for this effect.[1]

Pre-human global warming Further information: Paleoclimatology and temperature record

Curves of reconstructed temperature at two locations in Antarctica and a global record of variations in glacial ice volume. Today's date is on the left side of the graph

Changes in climate during the Phanerozoic (the last 542 million years). The recent period is located on the left-hand side of the plot. The earth has experienced natural global warming and cooling many times in the past. The recent Antarctic EPICA ice core spans 800,000 years, including eight glacial cycles with interglacial warming periods much hotter than current temperatures. The chart also shows the time of the last glacial maximum about 20,000 years ago. It is thought by some geologists[attribution needed] that a rapid buildup of greenhouse gases caused the Earth to experience global warming in the early Jurassic period, with average temperatures rising by 5 °C (9.0 °F). Research by the Open University indicates that this caused the rate of rock weathering to increase by 400%. As such weathering locks away carbon in calcite and dolomite, CO2 levels dropped back to normal over roughly the next 150,000 years.[42][43] Sudden releases of methane from clathrate compounds (the clathrate gun hypothesis) have been hypothesized as a cause for other past global warming events, including the Permian-Triassic extinction event and the Paleocene-Eocene Thermal Maximum. However, warming at the end of the last glacial period is thought not to be due to methane release.[44] Instead, natural variations in the Earth's orbit (Milankovitch cycles) are believed to have triggered the retreat of ice sheets by changing the amount of solar radiation received at high latitude and led to deglaciation. Using paleoclimate data for the last 500 million years, Veizer et al. (2000, Nature 408, pp. 698–701) concluded that long-term temperature variations are only weakly related to CO2 variations. Most paleoclimatologists believe this is because other factors, such as continental drift and mountain building have larger effects in determining very long-term climate. Shaviv and Veizer (2003) proposed that the largest long-term influence on temperature are variations in the flux of cosmic rays received by the Earth as the Solar System moves around the galaxy.[45] They argued that over geologic time-scales a change in CO2 concentrations comparable to doubling pre-industrial levels results in about 0.75 °C (1.35 °F) warming, less than the 1.5–4.5 °C (2.7–8.1 °F) reported by climate models.[46] Shaviv and Veizer (2004) acknowledge that this conclusion may only be valid on multi-million year time scales when glacial and geological feedback have had a

chance to establish themselves. Rahmstorf et al. argue that Shaviv and Veizer arbitrarily tuned their data, and that their conclusions are unreliable.[47] See also: Snowball Earth

Pre-industrial global warming Paleoclimatologist William Ruddiman has argued that human influence on the global climate began around 8,000 years ago with the start of forest clearing to provide land for agriculture and 5,000 years ago with the start of Asian rice irrigation.[48] He contends that forest clearing explains the rise in CO2 levels in the current interglacial that started 8,000 years ago, contrasting with the decline in CO2 levels seen in the previous three interglacials. He further contends that the spread of rice irrigation explains the breakdown in the last 5,000 years of the correlation between the Northern Hemisphere solar radiation and global methane levels, which had been maintained over at least the last eleven 22,000-year cycles. Ruddiman argues that without these effects, the Earth would be nearly 2 °C (3.6 °F) cooler and "well on the way" to a new ice age. Ruddiman's interpretation of the historical record, with respect to the methane data, has been disputed.[49]

Greenhouse gas From Wikipedia, the free encyclopedia

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Top: Increasing atmospheric CO2 levels as measured in the atmosphere and ice cores. Bottom: The amount of net carbon increase in the atmosphere, compared to carbon emissions from burning fossil fuel. Energy Portal Greenhouse gases are components of the atmosphere that contribute to the Greenhouse effect. Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occurring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities add to the levels of most of these naturally occurring gases.[1]

Contents [hide] • • • • • • • • •

1 The "Greenhouse effect" 2 Anthropogenic greenhouse gases 3 The role of water vapor 4 Increase of greenhouse gases 5 Removal from the atmosphere and global warming potential 6 Related effects 7 See also 8 References 9 External links o 9.1 Carbon dioxide emissions o 9.2 Methane emissions o

9.3 Policy and advocacy

[edit] The "Greenhouse effect" Main article: Greenhouse effect The greenhouse effect was discovered in 1824 by Joseph Fourier and first quantitatively investigated in 1896 by Svante Arrhenius. When sunlight reaches the surface of earth, some of it is absorbed and warms the earth. Because the Earth's surface is much cooler than the sun, it radiates energy at much longer wavelengths than the sun (see black body radiation and Wien's displacement law). Some energy in these longer wavelengths is absorbed by greenhouse gases in the atmosphere before it can be lost to space. The absorption of this longwave radiant energy warms the atmosphere (the atmosphere also is warmed by transfer of sensible and latent heat from the surface). Greenhouse gases also emit longwave radiation both upward to space and downward to the surface. The downward part of this longwave radiation emitted by the atmosphere is the "greenhouse effect." The term is in fact a misnomer, as this process is not the primary mechanism that warms greenhouses.

The major natural greenhouse gases are water vapour, which causes about 36-70% of the greenhouse effect on Earth (not including clouds); carbon dioxide, which causes 9-26%; methane, which causes 4-9%, and ozone, which causes 3-7%. It is not possible to state that a certain gas causes a certain percentage of the greenhouse effect, because the influences of the various gases are not additive. (The higher ends of the ranges quoted are for the gas alone; the lower ends, for the gas counting overlaps.)[2][3] Other greenhouse gases include, but are not limited to, nitrous oxide, sulfur hexafluoride, hydrofluorocarbons, perfluorocarbons and chlorofluorocarbons (see IPCC list of greenhouse gases). The major atmospheric constituents (nitrogen, N2 and oxygen, O2) are not greenhouse gases. This is because homonuclear diatomic molecules such as N2 and O2 neither absorb nor emit infrared radiation, as there is no net change in the dipole moment of these molecules when they vibrate. Molecular vibrations occur at energies that are of the same magnitude as the energy of the photons on infrared light. It is worth noting that late 19th century scientists experimentally discovered that N2 and O2 did not absorb infrared radiation (called, at that time, "dark radiation") and that CO2 and many other gases did absorb such radiation. It was recognized in the early 20th century that the known major greenhouse gases in the atmosphere did cause the earth's temperature to be higher than it would have been without the greenhouse gases.

[edit] Anthropogenic greenhouse gases

Global anthropogenic greenhouse gas emissions broken down into 8 different sectors for the year 2000. The concentrations of several greenhouse gases have increased over time.[4] Human activity increases the greenhouse effect primarily through release of carbon dioxide, but human influences on other greenhouse gases can also be important.[5] Some of the main sources of greenhouse gases due to human activity include: •

burning of fossil fuels and deforestation leading to higher carbon dioxide concentrations;

•

• •

livestock and paddy rice farming, land use and wetland changes, 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 major sources of atmospheric methane; use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes. agricultural activities, including the use of fertilizers, that lead to higher nitrous oxide concentrations.

Greenhouse gas emissions from industry, transportation and agriculture are very likely the main cause of recently observed global warming.[6].[7] Carbon dioxide, methane, nitrous oxide and three groups of fluorinated gasses (sulfur hexafluoride, HFCs, and PFCs) are the major greenhouse gases and the subject of the Kyoto Protocol, which entered into force in 2005.[8] CFCs, although greenhouse gasses, are regulated by the Montreal Protocol, which was motivated by CFCs' contribution to ozone depletion rather than by their contribution to global warming. Note that ozone depletion has only a minor role in greenhouse warming though the two processes often are confused.

[edit] The role of water vapor

Increasing water vapor at Boulder, Colorado. Water vapor is a naturally occurring greenhouse gas and accounts for the largest percentage of the greenhouse effect. Water vapor concentrations fluctuate regionally, but human activity does not directly affect water vapor concentrations except at very local scales. In climate models an increase in atmospheric temperature caused by the greenhouse effect due to anthropogenic gases will in turn lead to an increase in the water vapor content of the troposphere, with approximately constant relative humidity. The increased water vapor in turn leads to an increase in the greenhouse effect and thus a further increase in temperature; the increase in temperature leads to still further increase in

atmospheric water vapor; and the feedback cycle continues until equilibrium is reached. Thus water vapor acts as a positive feedback to the forcing provided by human-released greenhouse gases such as CO2[9] (but has never, so far, acted on Earth as part of a runaway feedback). Changes in water vapor may also have indirect effects via cloud formation. Intergovernmental Panel on Climate Change (IPCC) IPCC Third Assessment Report chapter lead author Michael Mann considers citing "the role of water vapor as a greenhouse gas" to be "extremely misleading" as water vapor can not be controlled by humans.[10][11][12] The IPCC report has discussed water vapor feedback in more detail.[13]

[edit] Increase of greenhouse gases Measurements from Antarctic ice cores show that just before industrial emissions began, atmospheric CO2 levels were about 280 parts per million by volume (ppm; the units µL/L are occasionally used and are identical to parts per million by volume). From the same ice cores it appears that CO2 concentrations stayed between 260 and 280 ppm during the preceding 10,000 years. Studies using evidence from stomata of fossilized leaves suggest greater variability, with CO2 levels above 300 ppm during the period 7,000-10,000 years ago,[14] though others have argued that these findings more likely reflect calibration/contamination problems rather than actual CO2 variability.[15][16] Since the beginning of the Industrial Revolution, the concentrations of many of the greenhouse gases have increased. The concentration of CO2 has increased by about 100 ppm (i.e., from 280 ppm to 380 ppm). The first 50 ppm increase took place in about 200 years, from the start of the Industrial Revolution to around 1973; the next 50 ppm increase took place in about 33 years, from 1973 to 2006. [2]PDF (96.8 KiB). Many observations are available on line in a variety of Atmospheric Chemistry Observational Databases. The greenhouse gases with the largest radiative forcing are: Relevant to radiative forcing

Gas

Current (1998) Increase over prePercentage increase Amount by volume industrial (1750)

Carbon dioxide

365 ppm {383 ppm(2007.01)}

87 ppm {105 ppm(2007.01)}

Methane

1,745 ppb

1,045 ppb

Radiative forcing (W/m2)

31% 1.46 {~1.532 {37.77%(2007.01)} (2007.01)} 150%

0.48

Nitrous oxide

314 ppb

44 ppb

16%

0.15

Global carbon dioxide emissions 1751–2000. Relevant to both radiative forcing and ozone depletion; all of the following have no natural sources and hence zero amounts pre-industrial Current (1998) Amount by volume

Radiative forcing (W/m2)

CFC-11

268 ppt

0.07

CFC-12

533 ppt

0.17

CFC-113

84 ppt

0.03

Carbon tetrachloride

102 ppt

0.01

HCFC-22

69 ppt

0.03

Gas

(Source: IPCC radiative forcing report 1994 updated (to 1998) by IPCC TAR table 6.1 [3][4]).

[edit] Removal from the atmosphere and global warming potential

Major greenhouse gas trends Aside from water vapor near the surface, which has a residence time of days, most greenhouse gases take a very long time to leave the atmosphere. Although it is not easy to know with precision how long, there are estimates of the duration of stay, i.e., the time which is necessary so that the gas disappears from the atmosphere, for the principal greenhouse gases. Greenhouse gases can be removed from the atmosphere by various processes: • •

•

•

•

as a consequence of a physical change (condensation and precipitation remove water vapor from the atmosphere). as a consequence of chemical reactions within the atmosphere. This is the case for methane. It is oxidized by reaction with naturally occurring hydroxyl radical, OH· and degraded to CO2 and water vapor at the end of a chain of reactions (the contribution of the CO2 from the oxidation of methane is not included in the methane GWP). This also includes solution and solid phase chemistry occurring in atmospheric aerosols. as a consequence of a physical interchange at the interface between the atmosphere and the other compartments of the planet. An example is the mixing of atmospheric gases into the oceans at the boundary layer. as a consequence of a chemical change at the interface between the atmosphere and the other compartments of the planet. This is the case for CO2, 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). as a consequence of 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).

•

as a consequence of dissociative ionization caused by high energy cosmic rays or lightning discharges, which break molecular bonds. For example, lightning forms N atoms from N2 which then react with O2 to form NO2.

Two scales can be used to describe the effect of different gases in the atmosphere. The first, the atmospheric lifetime, describes how long it takes to restore the system to equilibrium following a small increase in the concentration of the gas in the atmosphere. Individual molecules may interchange with other reservoirs such as soil, the oceans, and biological systems, but the mean lifetime refers to the decaying away of the excess. It is sometimes erroneously claimed that the atmospheric lifetime of CO2 is only a few years because that is the average time for any CO2 molecule to stay in the atmosphere before being removed by mixing into the ocean, uptake by photosynthesis, or other processes. This ignores the balancing fluxes of CO2 into the atmosphere from the other reservoirs. It is the net concentration changes of the various greenhouse gases by all sources and sinks that determines atmospheric lifetime, not just the removal processes. The second scale is global warming potential (GWP). The GWP depends on both the efficiency of the molecule as a greenhouse gas and its atmospheric lifetime. GWP is measured relative to the same mass of CO2 and evaluated for a specific timescale. Thus, if a molecule has a high GWP on a short time scale (say 20 years) but has only a short lifetime, it will have a large GWP on a 20 year scale but a small one on a 100 year scale. Conversely, if a molecule has a longer atmospheric lifetime than CO2 its GWP will increase with time. Examples of the atmospheric lifetime and GWP for several greenhouse gases include: •

•

• • • • •

CO2 has a variable atmospheric lifetime (approximately 200-450 years for small perturbations). Recent work indicates that recovery from a large input of atmospheric CO2 from burning fossil fuels will result in an effective lifetime of tens of thousands of years.[17][18] Carbon dioxide is defined to have a GWP of 1 over all time periods. Methane has an atmospheric lifetime of 12 ± 3 years and a GWP of 62 over 20 years, 23 over 100 years and 7 over 500 years. The decrease in GWP associated with longer times is associated with the fact that the methane is degraded to water and CO2 by chemical reactions in the atmosphere. Nitrous oxide has an atmospheric lifetime of 120 years and a GWP of 296 over 100 years. CFC-12 has an atmospheric lifetime of 100 years and a GWP(100) of 10600. HCFC-22 has an atmospheric lifetime of 12.1 years and a GWP(100) of 1700. Tetrafluoromethane has an atmospheric lifetime of 50,000 years and a GWP(100) of 5700. Sulfur hexafluoride has an atmospheric lifetime of 3,200 years and a GWP(100) of 22000.

Source : IPCC, table 6.7.

[edit] Related effects

MOPITT 2000 global carbon monoxide Carbon monoxide has an indirect radiative effect by elevating concentrations of methane and tropospheric ozone through scavenging of atmospheric constituents (e.g., the hydroxyl radical, OH) that would otherwise destroy them. Carbon monoxide is created when carbon-containing fuels are burned incompletely. Through natural processes in the atmosphere, it is eventually oxidized to carbon dioxide. Carbon monoxide has an atmospheric lifetime of only a few months[19] and as a consequence is spatially more variable than longer-lived gases. Another potentially important indirect effect comes from methane, which in addition to its direct radiative impact also contributes to ozone formation. Shindell et al (2005)[20] argue that the contribution to climate change from methane is at least double previous estimates as a result of this effect.[21]