### Emissions from land use & natural sources

#### Indicators:

CO2 emissions from land use CH4 emissions from land use and natural sources CO emissions from land Use | Organic carbon emissions from land use Black carbon emissions from land use NH3 emissions from land use and natural sources | N2O emissions from land use and natural sources NOx emissions from land use and natural sources VOC emissions from land use and natural sources SO2 emissions from land use and natural sources

The land use emissions model (LUEM) covers the following gases:

- Greenhouse gases (CH4, N2O)
- Ozone precursos (NOx, CO, NMVOC)
- Acidifying compounds (SO2)

For an explanation of these compounds, see definitions - chemical compounds.

The fluxes of CO2 between the terrestrial biosphere and the atmosphere are calculated separately by the Terrestrial Carbon Model (TCM).

The following land-use sources are distinguished. Gas species that are modeled with respect to the source are mentioned between brackets:

- biomass burning from deforestation (CO2, CH4, CO, OC, BC, NH3, NOx, NMVOC);
- biomass burning from fuel wood (CO2, CH4, CO, OC, BC, NH3, NOx, NMVOC);
- timber pools (CO2);
- savanna burning (CH4, CO, OC, BC, NH3, NOx, NMVOC);
- agricultural waste burning (CH4, CO, OC, BC, NH3, NOx, NMVOC);
- crop residues (N2O, NOx, NH3); Same as Crops/decomposition of crops?
- landfills (CH4);
- domestic sewage treatment (CH4, N2O);
- wetland rice fields (CH4);
- animals (CH4);
- animal waste (CH4, N2O, NH3);
- fertilizers (N2O, NOx, NH3);
- indirect sources (N2O);
- post-clearing effects (N2O);
- biological N fixation (N2O);
- stables (NH3).

The natural sources are:

- natural wetlands (CH4);
- natural soils (N2O, NOx, NH3);
- oceans (CH4, CO, N2O, SO2, NH3);
- volcanoes (CH4, SO2);
- methane hydrates (CH4);
- wildfires (CH4, CO);
- plants (CO);
- termites (CH4);
- lightning (NOx);
- natural vegetation (NMVOC).

#### CO2 emissions from land use |
unit:Pg/yr (Petagram C per year) dimension: region, source |

The CO2 emissions for land use stem from biomass burning, the decay of wood products and from vegetation regrowing towards its potential natural vegetation after clearing. In general, carbon is released during the first stage of the regrowth period directly after clearing (due to soil respiration). After this intial stage there will be a net uptake of carbon, expressed as a negative emission value. In 1995, about 25% of the global CO2 emissions were issued from the burning of wood and biomass during deforestation or shortly thereafter as fuel wood.

CO2 emissions from wood products (the so-called timber pools) are divided in two categories:

- pulpwood and particles (with an average lifetime of 10 years)
- saw logs, veneer and other industrial round wood (with an average lifetime of 100 years)

CO2 emissions are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS) to derive atmospheric concentrations of CO2.

Uptake of carbon by full grown natural vegetation due to CO2-fertilization is not shown here. It is shown as part of the indicators 'Carbon Flux' and 'Carbon Flux for each land cover type' in the indicator box on the Carbon Cycle (in other State-indicators).

#### CH4 emissions from land use & natural sources |  |
unit:Tg CH4/yr (Teragram of CH4 per year) dimension: region, source |

Methane stems from a variety of sources. A major source is microbial decomposition of organic material under anaerobic conditions. This process prevails in natural wetlands, wet rice cultivation and landfill sites for solid waste dumping. Methane is also formed in the digestive tract of ruminating animals and by various insects, the major species being termites (10-50 Tg CH4 per year). The burning of biomass is another source, coming next to fossil or non-living methane from methane hydrates.

For savanna burning, agricultural waste burning, landfilling and wet rice cultivation specific scenario assumptions related to changes in the emission factors and abatement of emissions (see scenario context) are made.

The methane emissions are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean sytem (AOS) to derive atmospheric concentrations.

| #### CO emissions from land use and natural sources
| unit:Tg C/yr (Teragram of C per year) dimension: region,source

Emissions of CO are mainly produced by the burning of biomass, of which burning during deforestation, burning of agricultural wastes and fuel wood, savanna fires and wildfires are explicitly modelled.

Specific scenario assumptions were used for savanna burning and agricultural waste burning (see scenario context).

CO emissons are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS) to derive atmospheric concentration of greenhouse gases.

#### Organic carbon emissions from land use |  |
unit:Tg C ? /yr (Teragram of C per year) dimension: region, source |

Emissions of organic carbon are mainly produced by the burning of ....

#### Black carbon emissions from land use |  |
unit:Tg C ? /yr (Teragram of C per year) dimension: region, source |

Emissions of black carbon are mainly produced by the burning of ....

#### NH3 emissions from land use and natural source |  |
unit:Tg C ? /yr (Teragram of C per year) dimension: region, source |  |

Emissions of NH3 are ....

#### N2O emissions from land use and natural sources |
unit:Tg /y (Teragram of N per year) dimension: region, source |

Nitrous oxide emissions are mostly formed in soils during nitrification and denitrification processes. The precise dynamics of nitrous oxide emissions are largely unknown, but are related to several sources, such as:

- N-fertilizer use, animal manures and biomass burning
- Aquatic sources (oceans and coastal waters, sewage treatment, freshwater systems, aquifers and irrigation)
- Global warming, which accelerates biological nitrous-oxide forming processes (i.e. biological N fixation)

The land-use related nitrous oxide emissions stem from application of synthetic N fertilizers and animal wastes to croplands and grasslands, animal waste management systems, grazing, soil incorporation of crop residues and cultivation of leguminous crops, as well as indirect sources caused by leaching of N and by human sewage. All these sources are calculated on the basis of IPCC Methodology for National Greenhouse Gas Emission Inventories.

Deforestation (i.e. land clearing) may lead to accelerated decomposition of litter, root material and soil organic matter in the first years after disturbance, causing a pulse of nitrous oxide emissions. This effect is taken into account only for tropical rain and seasonal forests, where in the first year after clearing, the nitrous oxide flux amounts to five times the flux of the original ecosystem, which then decreases linearly to the flux of the new ecosystem in the subsequent 10 years; this is usually lower than the flux from the original forest.

A global estimate is used for the nitrous oxide flux from aquatic sources, which includes an oceanic contribution.

Specific scenario assumptions were used for savanna burning and agricultural waste burning (see scenario context).

Nitrous oxide emissions are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS) to derive the atmospheric concentration of greenhouse gases.

#### NOx emissions from land use and natural sources |  |
unit:Tg N/yr (Teragram of N per year) dimension: region, source |

Land-use related emissions of nitrogen oxides stem from soils under natural vegetation, agricultural soils, soil incorporation of crop residues, burning of biomass during deforestation, wildfires, burning of agricultural wastes and fuel wood, and savanna fires.

Specific scenario assumptions were used for savanna burning and agricultural waste burning (see scenario context).

NOx emissions are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS) as input variables to parameterize the impact on OH and tropospheric ozone concentrations. Both species are important in atmospheric removal processes of carbon monoxide (CO), methane (CH4) and non-methane volatile organic compounds (NMVOC).

| #### NMVOC emissions from land use and natural sources
| unit:Tg NMVOC/yr (Teragram of NMVOC per year) dimension: region, source

The most important source of NMVOC is natural vegetation (mainly isoprenes and terpenes). Other sources are biomass burning during deforestation, burning of agricultural wastes, fuelwood and savanna fires.

Specific scenario assumptions were used for savanna burning and agricultural waste burning (see scenario context).

NMVOC emissions from the terrestrial system are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS), where they play a role in the atmospheric concentration of carbon monoxide (CO), through which the concentrations of methane and tropospheric ozone are influenced.

#### SO2 emissions from land use and natural sources |  |
unit:Tg S/y (Teragram of S per year) dimension: region, source |

Sulfur dioxide sources distinguished in the model are biomass burning due to deforestation, savanna and agricultural waste burning, and natural sources. The natural sources are mainly oceanic dimethylsulphide (DMS) emissions and to a lesser extent emissions from volcanoes.

SO2 emissions are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS), where they form sulfate aerosols that reflect sunlight and therefore have a cooling effect on climate. Due to their relative short lifetime, this effect is concentrated in areas where the emissions occur (i.e. the northern Hemisphere).