Потенциал глобального потепления

Потенциал глобального потепления ( GWP ) - это тепло, поглощаемое любым парниковым газом в атмосфере, кратное количеству тепла, которое может быть поглощено той же массой диоксида углерода ( CO
2). GWP равен 1 для CO
2. Для других газов это зависит от газа и временных рамок.

Эквивалент углекислого газа ( CO
2e или CO
2экв или CO
2-e) рассчитывается из GWP. Его можно измерить по весу или концентрации. Для любого количества любого газа это количество CO
2который согреет землю так же, как это количество этого газа. Таким образом, он обеспечивает общую шкалу для измерения воздействия различных газов на климат. Он рассчитывается как ПГП, умноженное на количество другого газа. Например, если газ имеет GWP 100, две тонны газа содержат CO.
2е 200 тонн, и 1 часть на миллион газа в атмосфере содержит CO
2е 100 частей на миллион.

Ценности [ править ]

Двуокись углерода является эталоном. Он имеет GWP, равный 1, независимо от используемого периода времени. Выбросы CO2 вызывают увеличение концентрации CO2 в атмосфере, которое продлится тысячи лет. ^[1] Оценки значений ПГП за 20, 100 и 500 лет периодически составляются и пересматриваются в отчетах Межправительственной группы экспертов по изменению климата :

• SAR (1995 год) ^[2]
• TAR (2001) ^[3]
• AR4 (2007) ^[4]
• AR5 (2013) ^[5]

Хотя последние отчеты отражают большую научную точность, страны и компании продолжают использовать значения SAR и AR4 для сравнения в своих отчетах о выбросах. AR5 пропустил 500-летние значения, но представил оценки GWP, включая обратную связь между климатом и углеродом (f) с большой степенью неопределенности. ^[5]

IPCC перечисляет многие другие вещества, не указанные здесь. ^[5] Некоторые из них имеют высокий ПГП, но лишь низкую концентрацию в атмосфере. Суммарное воздействие всех фторированных газов оценивается в 3% от всех выбросов парниковых газов. ^[10]

Значения, приведенные в таблице, предполагают, что анализируется одна и та же масса соединения; разные соотношения будут результатом превращения одного вещества в другое. Например, сжигание метана до диоксида углерода уменьшило бы воздействие глобального потепления, но в меньшем, чем 25: 1, раз, поскольку масса сожженного метана меньше, чем масса высвободившегося диоксида углерода (соотношение 1: 2,74). ^[11] Если вы начали с 1 тонны метана с ПГП 25, после сжигания у вас будет 2,74 тонны CO.
2, каждая тонна которого имеет ПГП 1. Это чистое сокращение ПГП на 22,26 тонны, что снижает эффект глобального потепления в соотношении 25: 2,74 (примерно в 9 раз).

Использование в Киотском протоколе и РКИК ООН [ править ]

В соответствии с Киотским протоколом в 1997 году Конференция Сторон стандартизировала международную отчетность, решив (решение 2 / CP.3), что значения ПГП, рассчитанные для Второго доклада об оценке МГЭИК, должны использоваться для преобразования различных выбросов парниковых газов в сопоставимый CO
2эквиваленты. ^{[12] [13]}

После некоторых промежуточных обновлений в 2013 году этот стандарт был обновлен Варшавским совещанием Рамочной конвенции ООН об изменении климата (РКИК ООН, решение 24 / CP.19), чтобы потребовать использования нового набора 100-летних значений ПГП. Они опубликовали эти значения в Приложении III и взяли их из 4-го оценочного отчета Межправительственной группы экспертов по изменению климата, опубликованного в 2007 году ^[14].

Эти оценки 2007 года по-прежнему используются для международных сравнений до 2020 года ^[15], хотя последние исследования эффектов потепления выявили другие значения, как показано в таблице выше.

Importance of time horizon[edit]

A substance's GWP depends on the number of years (denoted by a subscript) 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, it becomes less important. Thus methane has a potential of 34 over 100 years (GWP₁₀₀ = 34) but 86 over 20 years (GWP₂₀ = 86); conversely sulfur hexafluoride has a GWP of 22,800 over 100 years but 16,300 over 20 years (IPCC Third Assessment Report). 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 quoting a GWP it is important to give a reference to the calculation.

The GWP for a mixture of gases can be obtained from the mass-fraction-weighted average of the GWPs of the individual gases.^[16]

Commonly, a time horizon of 100 years is used by regulators.

Water vapour[edit]

Water vapour is one of the primary greenhouse gases, but some issues prevent its GWP to be calculated directly. It has a profound infrared absorption spectrum with more and broader absorption bands than CO
2, and also absorbs non-zero amounts of radiation in its low absorbing spectral regions.^[17] Next, its concentration in the atmosphere depends on air temperature and water availability; using a global average temperature of ~16 °C, for example, creates an average humidity of ~18,000ppm at sea level (CO
2 is ~400ppm^[18] and so concentrations of [H₂O]/[CO
2] ~ 45x). Unlike other GHG, water vapor does not decay in the environment, so an average over some time horizon or some other measure consistent with "time dependent decay," q.v., above, must be used in lieu of the time dependent decay of artificial or excess CO
2 molecules. Other issues complicating its calculation are the Earth's temperature distribution, and the differing land masses in the Northern and Southern hemispheres.

Criticism and other metrics[edit]

The Global Temperature change Potential (GTP) is another way to compare gases. While GWP estimates heat absorbed, GTP estimates the resulting rise in average surface temperature of the world, over the next 20, 50 or 100 years, caused by a greenhouse gas, relative to the temperature rise which the same mass of CO
2 would cause.^[5]Calculation of GTP requires modeling how the world, especially the oceans, will absorb heat.^[19]GTP is published in the same IPCC tables with GWP.^[5]

GWP* has been proposed to take better account of short-lived climate pollutants (SLCP) such as methane, relating a change in the rate of emissions of SLCPs to a fixed quantity of CO2.^[20]

Calculating the global warming potential[edit]

The GWP depends on the following factors:

• the absorption of infrared radiation by a given gas
• the spectral location of its absorbing wavelengths
• the atmospheric lifetime of the gas

A high GWP correlates with a large infrared absorption and a long atmospheric lifetime. The dependence of GWP on the wavelength of absorption is more complicated. Even if a gas absorbs radiation efficiently at a certain wavelength, this may not affect its GWP much if the atmosphere already absorbs most radiation at that wavelength. A gas has the most effect if it absorbs in a "window" of wavelengths where the atmosphere is fairly transparent. The dependence of GWP as a function of wavelength has been found empirically and published as a graph.^[21]

Because the GWP of a greenhouse gas depends directly on its infrared spectrum, the use of infrared spectroscopy to study greenhouse gases is centrally important in the effort to understand the impact of human activities on global climate change.

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 (infrared-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.^[22]

The radiative forcing capacity (RF) is the amount of energy per unit area, per unit time, absorbed by the greenhouse gas, that would otherwise be lost to space. It can be expressed by the formula:

${\displaystyle {\mathit {RF}}=\sum _{i=1}^{100}{\text{Abs}}_{i}\cdot F_{i}/\left({\text{path length}}\cdot {\text{density}}\right)}$

where the subscript i represents an interval of 10 inverse centimeters. Abs_i represents the integrated infrared absorbance of the sample in that interval, and F_i represents the RF for that interval.^{[verification needed]}

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.^[23] 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:

${\displaystyle {\mathit {GWP}}\left(x\right)={\frac {\int _{0}^{\mathit {TH}}a_{x}\cdot \left[x(t)\right]dt}{\int _{0}^{\mathit {TH}}a_{r}\cdot \left[r(t)\right]dt}}}$

where TH is the time horizon over which the calculation is considered; a_x 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 a_x and a_r 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., CO
2, 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 CO
2 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. Clarifying this, while increasing CO
2 has less and less effect on radiative absorption as ppm concentrations rise, more powerful greenhouse gases like methane and nitrous oxide have different thermal absorption frequencies to CO
2 that are not filled up (saturated) as much as CO
2, so rising ppms of these gases are far more significant.

Carbon dioxide equivalent[edit]

Carbon dioxide equivalent (CO
2e or CO
2eq or CO
2-e) is calculated from GWP. It can be measured in weight or concentration. For any amount of any gas, it is the amount of CO
2 which would warm the earth as much as that amount of that gas. Thus it provides a common scale for measuring the climate effects of different gases. It is calculated as GWP times amount of the other gas.

As weight, CO
2e is the weight of CO
2 which would warm the earth as much as a particular weight of some other gas;^[24]it is calculated as GWP times weight of the other gas. For example if a gas has GWP of 100, two tons of the gas have CO
2e of 200 tons, and 9 tons of the gas has CO
2e of 900 tons.

As concentration, CO
2e is the concentration of CO
2 which would warm the earth as much as a particular concentration of some other gas or of all gases and aerosols in the atmosphere; it is calculated as GWP times concentration of the other gas(es). For example CO
2e of 500 parts per million would reflect a mix of atmospheric gases which warm the earth as much as 500 parts per million of CO
2 would warm it.^[25][26]

CO
2e calculations depend on the time-scale chosen, typically 100 years or 20 years,^[27][28]since gases decay in the atmosphere or are absorbed naturally, at different rates.

The following units are commonly used:

• By the UN climate change panel (IPCC): billion metric tonnes = n×10⁹ tonnes of CO
  2 equivalent (GtCO
  2eq)^[29]
• In industry: million metric tonnes of carbon dioxide equivalents (MMTCDE)^[30] and MMT CO2 Eq.^[15]
• For vehicles: grams of carbon dioxide equivalent per mile (gCO
  2e/mile)^[31] or per kilometer (gCO
  2e/km)^[32]

For example, the table above shows GWP for methane over 20 years at 86 and nitrous oxide at 289, so emissions of 1 million tonnes of methane or nitrous oxide are equivalent to emissions of 86 or 289 million tonnes of carbon dioxide, respectively.

See also[edit]

• Carbon accounting
• Carbon footprint
• Emission standard
• List of refrigerants#List
• Emission factor
• Radiative forcing
• Total equivalent warming impact

References[edit]

Notes[edit]

Sources[edit]

IPCC reports[edit]

• Schimel, D.; Alves, D.; Enting, I.; Heimann, M.; et al. (1995). "Chapter 2: Radiative Forcing of Climate Change". Climate Change 1995: The Science of Climate Change. Contribution of Working Group I to the Second Assessment Report of the Intergovernmental Panel on Climate Change. pp. 65–132.
• Ramaswamy, V.; Boucher, O.; Haigh, J.; Hauglustaine, D.; et al. (2001). "Chapter 6: Radiative Forcing of Climate Change". Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. pp. 349–416.
• Forster, P.; Ramaswamy, V.; Artaxo, P.; Berntsen, T.; et al. (2007). "Chapter 2: Changes in Atmospheric Constituents and Radiative Forcing" (PDF). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. pp. 129–234.
• Myhre, G.; Shindell, D.; Bréon, F.-M.; Collins, W.; et al. (2013). "Chapter 8: Anthropogenic and Natural Radiative Forcing" (PDF). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. pp. 659–740.

Other sources[edit]

• Alvarez (2018). "Assessment of methane emissions from the U.S. oil and gas supply chain". Science. 361 (6398): 186–188. doi:10.1126/science.aar7204. PMC 6223263. PMID 29930092.
• Etminan, M.; Myhre, G.; Highwood, E. J.; Shine, K. P. (2016-12-28). "Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing: Greenhouse Gas Radiative Forcing". Geophysical Research Letters. 43 (24): 12, 614–12, 623. doi:10.1002/2016GL071930.
• Derwent, R.G. (2018-10-07). "Hydrogen for Heating: Atmospheric Impacts. A literature review" (PDF). BEIS Research Paper.
• Morton, Adam (2020-08-26). "Methane released in gas production means Australia's emissions may be 10% higher than reported". The Guardian. ISSN 0261-3077. Retrieved 2020-08-26.
• Olivier, J.G.J.; Peters, J.A.H.W. (2020). Trends in global CO2 and total greenhouse gas emissions (2020) (PDF) (Report). The Hague: PBL Netherlands Environmental Assessment Agency.

External links[edit]

• List of Global Warming Potentials and Atmospheric Lifetimes from the U.S. EPA
• GWP and the different meanings of CO2e explained

Bibliography[edit]

• Gohar and Shine, Equivalent CO
  2 and its use in understanding the climate effects of increased greenhouse gas concentrations, Weather, Nov 2007, pp. 307–311.