http://en.wikipedia.org/wiki/Global_warming_potential
Global warming potential From Wikipedia, the free encyclopedia
Global warming potential (GWP) is a measure of how much a given mass of greenhouse gas is estimated to
contribute to global warming. It is a relative scale which compares the gas in question to that of the same mass
of carbon dioxide (whose GWP is by definition 1). A GWP is calculated over a specific time interval and the
value of this must be stated whenever a GWP is quoted or else the value is meaningless.
[edit] Calculation of GWP
Just as radiative forcing provides a simplified means of comparing the various factors that are believed to
influence the climate system to one another, Global Warming Potentials (GWPs) are one type of simplified
index based upon radiative properties that can be used to estimate the potential future impacts of emissions of
different gases upon the climate system in a relative sense.
GWP is based on a number of factors, including the radiative efficiency (heat-absorbing ability) of each gas
relative to that of carbon dioxide, as well as the decay rate of each gas (the amount removed from the
atmosphere over a given number of years) relative to that of carbon dioxide [1].
The Intergovernmental Panel on Climate Change (IPCC) provides the generally accepted values for GWP,
which changed slightly between 1996 and 2001. An exact definition of how GWP is calculated is to be found in
the IPCC's 2001 Third Assessment Report. The GWP is defined as the ratio of the time-integrated radiative
forcing from the instantaneous release of 1 kg of a trace substance relative to that of 1 kg of a reference gas:
where: TH is the time horizon over which the calculation is considered; ax is the radiative efficiency due to a
unit increase in atmospheric abundance of the substance (i.e., Wm-2 kg-1) and [x(t)] is the time-dependent decay
in abundance of the substance following an instantaneous release of it at time t=0. The denominator contains the
corresponding quantities for the reference gas (i.e. CO2). The radiative efficiencies ax and ar are not necessarily
constant over time. While the absorption of infrared radiation by many greenhouse gases varies linearly with
their abundance, a few important ones display non-linear behaviour for current and likely future abundances
(e.g., CO2, CH4, and N2O). For those gases, the relative radiative forcing will depend upon abundance and
hence upon the future scenario adopted.
Since all GWP calculations are a comparison to CO2 which is non-linear, all GWP values are affected.
Assuming otherwise as is done above will lead to lower GWPs for other gases than a more detailed approach
would.
[edit] GWP used in Kyoto protocol
Under the Kyoto protocol, the Conference of the Parties decided (decision 2/CP.3) [2] that the values of GWP
calculated for the IPCC Second Assessment Report are to be used for converting the various greenhouse gas
emissions into comparable CO2 equivalents when computing overall sources and sinks.
[edit] Importance of time horizon
Note that a substance's GWP depends on the timespan over which the potential is calculated. A gas which is
quickly removed from the atmosphere may initially have a large effect but for longer time periods as it has been
removed becomes less important. Thus methane has a potential of 23 over 100 years but 62 over 20 years;
conversely sulfur hexafluoride has a GWP of 22,000 over 100 years but 15,100 over 20 years (IPCC TAR). The
GWP value depends on how the gas concentration decays over time in the atmosphere. This is often not
precisely known and hence the values should not be considered exact. For this reason when quoted a GWP it is
important to give a reference to the calculation.
The GWP for a mixture of gases can not be determined from the GWP of the constituent gases by any form of
simple linear addition.
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Generally, it is by regulators (i.e. CARB) the time horizon of 100 years.
[edit] GWP values
Carbon dioxide has a GWP of exactly 1 (since it is the baseline unit to which all other greenhouse gases are
compared.)
GWP values and lifetimes from IPCC TAR [3]
GWP Time horizon
Gas
Lifetime (years)
20 years 100 years 500 year
Methane
12
62
23
7
Nitrous oxide
114
275
296
156
HFC-134a (hydrofluorocarbon) 13.8
3300
1300
400
HFC-23 (hydrofluorocarbon)
260
9400
12000
10000
sulfur hexafluoride
3200
15100
22200
32400
A GWP is not usually calculated for Water vapour, largely because it is not relevant; see greenhouse gas.
http://en.wikipedia.org/wiki/Greenhouse_gas
Greenhouse gas From Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Image:Carbon_History_and_Flux-2.png
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.
Greenhouse gases (GHG) 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 such as burning
of fossil fuel and coal.[1] Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and
ozone.
[edit] The "Greenhouse effect" Main article: Greenhouse effect
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When sunlight reaches the surface of the 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 does the sun. The
atmosphere absorbs these longer wavelengths more effectively than it does the shorter wavelengths from the sun.
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 a misnomer, as this process is not the mechanism that warms
greenhouses.
The major natural greenhouse gases are water vapor, 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
http://en.wikipedia.org/wiki/Image:Greenhouse_Gas_by_Sector.png
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:
Greenhousegas_wiki.doc
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

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 gases, 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 in the popular media.
[edit] The role of water vapor
http://en.wikipedia.org/wiki/Image:BAMS_climate_assess_boulder_water_vapor_2002.png
Increasing water vapor at Boulder, Colorado.
Water vapor is a naturally occurring greenhouse gas and accounts for the largest percentage of the greenhouse
effect, between 36% and 90% [2]. Water vapor concentrations fluctuate regionally, but human activity does not
directly affect water vapor concentrations except at local scales (for example, near irrigated fields).
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] 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 is quoted as saying, "It is extremely misleading, however, when scientists cite the role of water
vapor as a greenhouse gas," because it can not be controlled by humans.[10][11][12] The IPCC report has discussed
water vapor feedback in more detail.[13]
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[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. [3]PDF(96.8KiB). 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
Current (1998) Amount
Increase over
Radiative forcing
Gas
Percentage increase
by volume
pre-industrial (1750)
(W/m2)
Carbon
365 ppm {383
87 ppm {105
31%
1.46 {~1.532
dioxide
ppm(2007.01)}
ppm(2007.01)}
{37.77%(2007.01)}
(2007.01)}
Methane
1,745 ppb
1,045 ppb
150%
0.48
Nitrous
314 ppb
44 ppb
16%
0.15
oxide
http://en.wikipedia.org/wiki/Image:Global_Carbon_Emission_by_Type.png
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
Gas
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
(Source: IPCC radiative forcing report 1994 updated (to 1998) by IPCC TAR table 6.1 [4][5]).
[edit] Removal from the atmosphere and global warming potential
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http://en.wikipedia.org/wiki/Image:Major_greenhouse_gas_trends.png
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 Global warming potential). 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
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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
http://en.wikipedia.org/wiki/Image:Mopitt_first_year_carbon_monoxide.jpg
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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]
[edit] References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
^ EPA's Clean Air Markets - Climate Change
^ Kiehl, J. T.; Kevin E. Trenberth (February 1997). "Earth’s Annual Global Mean Energy Budget" (PDF). Bulletin of the American Meteorological
Society 78 (2): 197-208. Retrieved on 2006-05-01.
^ Water vapour: feedback or forcing?. RealClimate (6 Apr 2005). Retrieved on 2006-05-01.
^ Climate Change 2001: Working Group I: The Scientific Basis: C.1 Observed Changes in Globally Well-Mixed Greenhouse Gas Concentrations
and Radiative Forcing. Retrieved on 2006-05-01.
^ Climate Change 2001: Working Group I: The Scientific Basis: figure 6-6. Retrieved on 2006-05-01.
^ EPA's Clean Air Markets - Climate Change
^ Climate Change 2007: The Physical Science Basis. Summary for PolicymakersPDF (1.25 MiB)
^ Lerner & K. Lee Lerner, Brenda Wilmoth (2006). Environmental issues : essential primary sources.". Thomson Gale. Retrieved on 2006-09-11.
^ Robust Responses of the Hydrological Cycle to Global Warming
^ GOP Senators Blame Nature for Climate Change
^ Water vapour: feedback or forcing?
^ Calculating the greenhouse effect
^ 7.2.1.1 Water vapour feedback
^ Friederike Wagner, Bent Aaby and Henk Visscher (2002). "Rapid atmospheric CO2 changes associated with the 8,200-years-B.P. cooling event".
PNAS 99 (19): 12011-12014. DOI:10.1073/pnas.182420699.
^ Andreas Indermühle, Bernhard Stauffer, Thomas F. Stocker (1999). "Early Holocene Atmospheric CO2 Concentrations". Science 286 (5446):
1815. DOI:10.1126/science.286.5446.1815a. Early Holocene Atmospheric CO2 Concentrations. Science. Retrieved on May 26, 2005.
^ H.J. Smith, M Wahlen and D. Mastroianni (1997). "The CO2 concentration of air trapped in GISP2 ice from the Last Glacial Maximum-Holocene
transition". Geophysical Research Letters 24 (1): 1-4.
^ Archer, David (2005). "Fate of fossil fuel CO2 in geologic time". Journal of Geophysical Research 110, C09S05. DOI:10.1029/2004JC002625.
^ Caldeira, Ken and Wickett, Michael E. (2005). "Ocean model predictions of chemistry changes from carbon dioxide emissions to the atmosphere
and ocean". Journal of Geophysical Research 110, C09S04. DOI:10.1029/2004JC002671.
^ Impact of Emissions, Chemistry, and Climate on Atmospheric Carbon Monoxide: 100-year Predictions from a Global Chemistry-Climate
ModelPDF (115 KiB)
^ Shindell, Drew T.; Faluvegi, Greg; Bell, Nadine; Schmidt, Gavin A. "An emissions-based view of climate forcing by methane and tropospheric
ozone", Geophysical Research Letters, Vol. 32, No. 4 [1]
^ Methane's Impacts on Climate Change May Be Twice Previous Estimates
http://en.wikipedia.org/wiki/Radiative_forcing
Radiative forcing From Wikipedia, the free encyclopedia
In climate science, radiative forcing is defined as (loosely) the difference between the incoming radiation
energy and the outgoing radiation energy in a given climate system. A positive forcing (more incoming energy)
tends to warm the system, while a negative forcing (more outgoing energy) tends to cool it. Possible sources of
radiative forcing are changes in insolation (incident solar radiation), or the effects of variations in the amount of
radiatively active gases present. Because the Intergovernmental Panel on Climate Change (IPCC) regularly
assesses the radiative forcing, it also has a more specific technical definition - see "IPCC usage" section.
[edit] Radiation balance
Most of the energy which affects Earth's weather comes from the Sun. The planet and its atmosphere absorb
and reflect some of the energy, with that which is absorbed tending to produce warming. An amount of heat is
radiated back into space, tending to cool the planet. The balance between absorbed and radiated energy
determines the average temperature. The planet is warmer than it would be in the absence of the atmosphere:
see greenhouse effect for details and Radiation Balance for a mathematical explanation.
The radiation balance can be altered by factors such as intensity of solar energy, reflection by clouds or gases,
absorption by various gases or surfaces, and emission of heat by various materials. Any such alteration is a
radiative forcing, and causes a new balance to be reached. In the real world this happens continuously as
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sunlight hits the surface, clouds and aerosols form, the concentrations of atmospheric gases vary, and seasons
alter the ground cover.
[edit] IPCC usage Changes in radiative forcings between 1750 and 2005 as estimated by the IPCC.
http://upload.wikimedia.org/wikipedia/en/b/bb/Radiative-forcings.svg
This is a lossless scalable vector image. Base size: 600 × 480 pixels.
[edit] Summary
Global average radiative forcing estimates and ranges in 2005 for anthropogenic greenhouse gases and other
important agents and mechanisms.
Understanding global warming requires understanding the changes in climate forcings that have occurred since
the industrial revolution. These include positive forcing from increased greenhouse gases negative forcing from
increased sulphate aerosols and poorly constrained forcings from indirect areosol feedbacks as well as minor
contributions from solar variability and other factors. The poorly constrained aerosol effects results from both
limited physical undersanding of how aerosols interact with the atmosphere and limited knowledge of aerosol
concentrations during the pre-industrial period. This is a significant source of uncertainty in comparing modern
climate forcings to past states.
Contrary to the impression given by this figure, it is not possible to simply sum the radiative forcing
contributions from all sources and obtain a total forcing. This is because different forcing terms can interact to
either amplify or interfere with each other. For example, in the case of greenhouse gases, two different gases
may share the same absorption bands thus partially limiting their effectiveness when taken in combination.
The term “radiative forcing” has been employed in the IPCC Assessments with a specific technical meaning
to denote an externally imposed perturbation in the radiative energy budget of the Earth’s climate system,
which may lead to changes in climate parameters [1]. The exact definition used is:
The radiative forcing of the surface-troposphere system due to the perturbation in or the
introduction of an agent (say, a change in greenhouse gas concentrations) is the change in net
(down minus up) irradiance (solar plus long-wave; in Wm-2) at the tropopause AFTER allowing
for stratospheric temperatures to readjust to radiative equilibrium, but with surface and
tropospheric temperatures and state held fixed at the unperturbed values. [2]
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In the context of climate change, the term forcing is restricted to changes in the radiation balance of the
surface-troposphere system imposed by external factors, with no changes in stratospheric dynamics, without any
surface and tropospheric feedbacks in operation (i.e., no secondary effects induced because of changes in
tropospheric motions or its thermodynamic state), and with no dynamically-induced changes in the amount and
distribution of atmospheric water (vapour, liquid, and solid forms).
[edit] Related measures
Radiative forcing is intended as a useful way to compare different causes of perturbations in a climate system.
Other possible tools can be constructed for the same purpose: for example Shine et al, An alternative to
radiative forcing for estimating the relative importance of climate change mechanisms, GEOPHYSICAL
RESEARCH LETTERS, 2003 say "...recent experiments indicate that for changes in absorbing aerosols and
ozone, the predictive ability of radiative forcing is much worse... we propose an alternative, the 'adjusted
troposphere and stratosphere forcing'. We present GCM calculations showing that it is a significantly more
reliable predictor of this GCM's surface temperature change than radiative forcing. It is a candidate to
supplement radiative forcing as a metric for comparing different mechanisms...". In this quote, the word
"predictive" may be confusing: it refers to the ability of the tool to help explain the response, not to the ability
of GCMs to forecast climate change
Image:IPCC Radiative Forcings.png From Wikipedia, the free encyclopedia
http://upload.wikimedia.org/wikipedia/en/0/05/IPCC_Radiative_Forcings.png
IPCC_Radiative_Forcings.png (600 × 443 pixel, file size: 24 KB, MIME type: image/png)
[edit] Summary
Changes in radiative forcings between 1750 and 2000 based on IPCC estimates. Found at [1]
Understanding global warming requires understanding the changes in climate forcings that have occurred since
the industrial revolution as well as those that applied before. These include positive forcing from increased
greenhouse gases negative forcing from increased sulphate aerosols and poorly constrained forcings from
indirect areosol feedbacks as well as minor contributions from solar variability and other factors. The poorly
constrained aerosol effects results from both limited physical undersanding of how aerosols interact with the
atmosphere and limited knowledge of aerosol concentrations during the pre-industrial period. This is a
significant source of uncertainty in comparing modern climate forcings to past states.
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Contrary to the impression given by this figure, it is not possible to simply sum the radiative forcing
contributions from all sources and obtain a total forcing. This is because different forcing terms can interact to
either amplify or interfere with each other. For example, in the case of greenhouse gases, two different gases
may share the same absorption bands thus partially limiting their effectiveness when taken in combination.
[edit] Fair use rationale
 This figure is one of the more well-known IPCC images from the Third Assessment Report
It is used here to efficiently summarize the scientific understanding of radiative forcings.
 It is believed that the educational use of this small portion of the non-profit IPCC reports is
consistent with United States fair use doctrines.
This work is copyrighted and unlicensed. It does not fall into one of the blanket fair use categories
listed at Wikipedia:Fair use#Images or Wikipedia:Fair use#Audio_clips. However, it is believed that
the use of this work in the article "radiative forcing":
This work is copyrighted and unlicensed. It does not fall into one of the blanket fair use categories
listed at Wikipedia:Fair use#Images or Wikipedia:Fair use#Audio_clips. However, it is believed that
the use of this work in the article "greenhouse gases":.
File history
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Click on date to download the file or see the image uploaded on that date.
 (del) (cur) 00:29, 21 June 2006 . . Keenan Pepper (Talk | contribs) . . 600×443 (24,436 bytes)
(==Summary== Changes in radiative forcings between 1750 and 2000 based on IPCC estimates.
Found at [http://www.grida.no/climate/ipcc_tar/wg1/figspm-3.htm] Understanding global
warming requires understanding the changes in climate forc)
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