Emission intensity


An emission intensity is the emission rate of a given pollutant relative to the intensity of a specific activity, or an industrial production process; for example grams of carbon dioxide released per megajoule of energy produced, or the ratio of greenhouse gas emissions produced to gross domestic product. Emission intensities are used to derive estimates of air pollutant or greenhouse gas emissions based on the amount of fuel combusted, the number of animals in animal husbandry, on industrial production levels, distances traveled or similar activity data. Emission intensities may also be used to compare the environmental impact of different fuels or activities. In some case the related terms emission factor and carbon intensity are used interchangeably. The jargon used can be different, for different fields/industrial sectors; normally the term "carbon" excludes other pollutants, such as particulate emissions. One commonly used figure is carbon intensity per kilowatt-hour, which is used to compare emissions from different sources of electrical power.

Methodologies

Different methodologies can be used to assess the carbon intensity of a process. Among the most used methodologies there are:
  • The whole life-cycle assessment : this includes not only the carbon emissions due to a specific process, but also those due to the production and end-of-life of materials, plants and machineries used for the considered process. This is a quite complex method, requiring a big set of variables.
  • The well-to-wheels, commonly used in the Energy and Transport sectors: this is a simplified LCA considering the emissions of the process itself, the emissions due to the extraction and refining of the material used in the process, but excluding the emissions due to the production and end-of-life of plants and machineries. This methodology is used, in the US, by the GREET model and in Europe in the .
  • WTW-LCA hybrid methods, trying to fill in the gap between the WTW and LCA methods. In example, for an Electric Vehicle, an hybrid method considering also the GHG due to the manufacturing and the end of life of the battery gives GHG emissions 10–13% higher, compared to the WTW
  • Methods not considering LCA aspects but only the emissions occurring during a specific process; i.e. just the combustion of a fuel in a power plant, without considering the Upstream emissions.
Different calculation methods can lead to different results. The results can largely vary also for different geographic regions and timeframes considered for the calculations. For example, Chinese oil fields emit between 1.5 and more than 40 g of CO2e per MJ with about 90% of all fields emitting 1.5–13.5 g CO2e. Such highly skewed carbon intensity patterns necessitate disaggregation of seemingly homogeneous emission activities and proper consideration of many factors for understanding.

Estimating emissions

Emission factors assume a linear relation between the intensity of the activity and the emission resulting from this activity:
Emissionpollutant = Activity * Emission Factorpollutant
Intensities are also used in projecting possible future scenarios such as those used in the IPCC assessments, along with projected future changes in population, economic activity and energy technologies. The interrelations of these variables is treated under the so-called Kaya identity.
The level of uncertainty of the resulting estimates depends significantly on the source category and the pollutant. Some examples:
  • Carbon dioxide emissions from the combustion of fuel can be estimated with a high degree of certainty regardless of how the fuel is used as these emissions depend almost exclusively on the carbon content of the fuel, which is generally known with a high degree of precision. The same is true for sulphur dioxide, since sulphur contents of fuels are also generally well known. Both carbon and sulphur are almost completely oxidized during combustion and all carbon and sulphur atoms in the fuel will be present in the flue gases as CO2 and SO2 respectively.
  • In contrast, the levels of other air pollutants and non-CO2 greenhouse gas emissions from combustion depend on the precise technology applied when fuel is combusted. These emissions are basically caused by either incomplete combustion of a small fraction of the fuel.
  • Nitrous oxide emissions from agricultural soils are highly uncertain because they depend very much on both the exact conditions of the soil, the application of fertilizers and meteorological conditions.

    Electric generation

A literature review of numerous total life cycle energy sources emissions per unit of electricity generated, conducted by the Intergovernmental Panel on Climate Change in 2011, found that the emission value, that fell within the 50th percentile of all total life cycle emissions studies were as follows.
TechnologyDescription50th percentile
Hydroelectricreservoir4
Windonshore12
Nuclearvarious generation II reactor types16
Biomassvarious230
Solar thermalparabolic trough22
Geothermalhot dry rock45
Solar PVPolycrystalline silicon46
Natural gasvarious combined cycle turbines without scrubbing469
Coalvarious generator types without scrubbing1001

Fuel/
Resource		Thermal
g/MJth		Energy Intensity
W·hth/W·he		Electric
g/kW·he
wood
Peat
CoalB:91.50–91.72
Br:94.33
88		B:2.62–2.85
Br:3.46
3.01		B:863–941
Br:1,175
955
Oil
Natural gascc:68.20
oc:68.40
51		cc:2.35
oc:3.05 		cc:577
oc:751
599
Geothermal
Power		~TL0–1
TH91–122
Uranium
Nuclear power		WL0.18
WH0.20 		WL60
WH65
Hydroelectricity
Conc. Solar Pwr±15#
Photovoltaics
Wind power

Note: 3.6 MJ = megajoule 1 kW·h = kilowatt-hour, thus 1 g/MJ = 3.6 g/kW·h.
Legend:,,,,,,,,.

Carbon intensity of regions

The following tables show carbon intensity of GDP in market exchange rates and purchasing power parities. Units are metric tons of carbon dioxide per thousand year 2005 US dollars. Data are taken from the US Energy Information Administration. Annual data between 1980 and 2009 are averaged over three decades: 1980–89, 1990–99, and 2000–09.
1980–891990–992000–09
Africa1.131491.207021.03995
Asia & Oceania0.862560.830150.91721
Central & South America0.558400.572780.56015
EurasiaNA3.317862.36849
Europe0.368400.372450.30975
Middle East0.987791.214751.22310
North America0.693810.586810.48160
World0.621700.661200.60725

1980–891990–992000–09
Africa0.488440.502150.43067
Asia & Oceania0.661870.592490.57356
Central & South America0.300950.307400.30185
EurasiaNA1.431611.02797
Europe0.404130.388970.32077
Middle East0.516410.656900.65723
North America0.667430.566340.46509
World0.544950.548680.48058

In 2009 CO2 intensity of GDP in the OECD countries reduced by 2.9% and amounted to 0.33 kCO2/$05p in the OECD countries.. The USA posted a higher ratio of 0.41 kCO2/$05p while Europe showed the largest drop in CO2 intensity compared to the previous year. CO2 intensity continued to be roughly higher in non-OECD countries. Despite a slight improvement, China continued to post a high CO2 intensity. CO2 intensity in Asia rose by 2% during 2009 since energy consumption continued to develop at a strong pace. Important ratios were also observed in countries in CIS and the Middle East.

Carbon intensity in Europe

Total CO2 emissions from energy use were 5% below their 1990 level in 2007. Over the period 1990–2007, CO2 emissions from energy use have decreased on average by 0.3%/year although the economic activity increased by 2.3%/year. After dropping until 1994, the CO2 emissions have increased steadily until 2003 and decreased slowly again since. Total CO2 emissions per capita decreased from 8.7 t in 1990 to 7.8 t in 2007, that is to say a decrease by 10%.
Almost 40% of the reduction in CO2 intensity is due to increased use of energy carriers with lower emission factors.
Total CO2 emissions per unit of GDP, the “CO2 intensity”, decreased more rapidly than energy intensity: by 2.3%/year and 1.4%/year, respectively, on average between 1990 and 2007.
However, while the reports from 2007 suggest that the CO2 emissions are going down recent studies find that the global emissions are rapidly escalating. According to the Climate Change 2022 Mitigation of Climate Change report, conducted by the IPCC, it states that it 2019 the world emissions output was 59 gigatonnes. This shows that global emissions has grown rapidly, increasing by about 2.1% each year compared from the previous decade.
The Commodity Exchange Bratislava has calculated carbon intensity for Voluntary Emissions Reduction projects carbon intensity in 2012 to be 0.343 tn/MWh.
A 2024 report shows an increase of renewable energy production, reaching 50% of the energy mix
According to data from the European Commission, in order to achieve the EU goal of decreasing greenhouse gas emissions by at least 55% by 2030 compared to 1990, EU-based energy investment has to double from the previous decade to more than €400 billion annually this decade. This includes the roughly €300 billion in yearly investment required for energy efficiency and the roughly €120 billion required for power networks and renewable energy facilities.