InVest

Earth's ecosystems are vital for influencing climate change caused by carbon dioxide, as they store more carbon than the atmosphere. The InVEST model uses land use maps and reserves in four carbon deposits (aerial biomass, underground biomass, soil, dead organic matter) to estimate the amount of carbon currently stored in a landscape or the amount of carbon sequestered across the landscape. of time. You can create a model that uses additional data on the market or social value of sequestered carbon, its annual exchange rate and a discount rate to estimate the value of this ecosystem service to society. The limitations of the model include a greatly simplified carbon cycle, a supposed linear shift in carbon sequestration over time, and potentially inaccurate discount rates.

Forests, grasslands, peatlands and other terrestrial ecosystems collectively collect far more carbon than the atmosphere. By storing this carbon in wood, other biomass and soil, ecosystems keep CO2 out of the atmosphere, contributing to climate change. In addition to carbon storage, many systems also continue to accumulate in plants and soil over time, allowing more carbon to be "captured" each year. Changes in these systems (fires, diseases, vegetation...) can release large amounts of CO2 or, conversely, storage (restoration of forests, agricultural practices...).

The social value of a ton of carbon sequestered is equal to the social damage avoided by not releasing the ton of carbon into the atmosphere. Social cost calculations are complicated and controversial, but have resulted in estimates ranging from $9.55 to $84.55 per ton of CO2 released into the atmosphere.

Calculation using InVEST

The InVEST "Carbon Storage and Sequestration" model estimates the current amount of carbon stored in a landscape and assesses the amount of carbon sequestered over time.

First, it adds the biophysical amount of carbon stored in four carbon pools according to land use/land cover (LULC) maps:

• airborne living biomass,

• subterranean living biomass

• ground

• dead organic matter

If, in addition, we provide a future LULC map, the carbon sequestration component of the model estimates the expected change in carbon stocks over time. This part of the model values the amount of carbon sequestered as an environmental service using additional data on the market value or social cost of carbon, its annual exchange rate and a discount rate.

The model

The storage of carbon in a parcel of land depends largely on the size of four carbon reservoirs: aerial biomass, underground biomass, soil and dead organic matter. InVEST's carbon storage and sequestration model adds the amount of carbon stored in these reservoirs according to the land use maps and classifications we provide.

• Aerial biomass comprises all living plant material on the ground (e.g. bark, trunks, branches, leaves).

• Underground biomass includes the living root systems of the aerial biomass.

• Soil organic matter is the organic component of the soil and represents the largest terrestrial carbon pool.

• Dead organic matter includes rubbish, as well as dead wood, both lying and standing.

Using maps of land use and land cover types and the amount of carbon stored in carbon reservoirs, this model estimates the net amount of carbon stored in a plot of land over time and the market value of the carbon sequestered in the remaining stocks.

The limitations of the model include an oversimplified carbon cycle, an assumed linear change in carbon sequestration over time, and potentially inaccurate discount rates. Important biophysical conditions for carbon sequestration, such as rates of photosynthesis and the presence of active soil organisms, are also not included in the model.

Required information

Note that all GIS inputs must be in the same projected coordinate system and in units of linear meters.

1. Current land use/land cover (mandatory): Land use/land cover (LULC) raster for each pixel, where each unique integer represents a different land use/land cover class. All values in this raster MUST have corresponding entries in the Carbon Pools table.

Current land cover calendar year (required for sequestration and valuation): The year represented by the current LULC map, to be used in the calculation of sequestration and economic values.

2. Carbon stocks (required): A CSV (comma-separated values) table of LULC classes, containing data on the carbon stored in each of the four key stocks for each LULC class If information on some carbon reservoirs is not available, the reservoirs can be estimated from other reservoirs or they can be omitted leaving all reservoir values equal to 0. The table should contain the following columns:

• lucode: unique integer for each LULC class (e.g. 1 for forest, 3 for grassland, etc.)

• c_above: Carbon density in aboveground biomass [units: megagrams/hectare]

• c_below: Carbon density in belowground biomass [units: megagrams/hectare]

• c_soil: Carbon density in soil [units: megagrams/hectare]

• c_dead: Carbon density in dead matter [units: megagrams/hectare]

3. Future land cover (required for sequestration and assessment): Land use/land cover (LULC) raster for each pixel, where each unique integer represents a different land use/land cover class. All values in this raster MUST have corresponding entries in the Carbon Pools table.

Future calendar year of land cover (required for sequestration and valuation): The year represented by the Future LULC map, to be used in the calculation of sequestration and economic values.

4. Economic data (required for valuation):

Price/metric ton of carbon (V in the following equation): Price expressed in currency per metric ton of carbon. For applications interested in estimating the total value of carbon sequestration, we recommend value estimates based on the damage costs associated with the release of an additional ton of carbon: the social cost of carbon (SCC). Stern (2007), Tol (2009) and Nordhaus (2007a) present estimates of SCC. For example, two SCC estimates we have used from Tol (2009) are $66 and $130 (in 2010 US dollars).

Market discount on carbon price (r in the following equation): a whole percentage value that reflects society's preference for immediate benefits over future benefits. A default value is 7% per year, which is one of the market discount rates recommended by the US government for the assessment of costs and benefits of environmental projects. However, this rate will depend on the country and landscape being assessed and should be selected according to local requirements. Philosophical arguments have been made for using a lower discount rate when modelling the dynamics related to climate change, which users may consider using. If the rate is set at 0%, monetary values are not discounted.

Annual variation rate in the price of carbon (c in the following equation): a whole percentage value that adjusts the value of carbon sequestered as the impact of emissions on expected climate change-related damage changes over time. Setting this rate above 0% suggests that the social value of carbon sequestered in the future is lower than the value of carbon sequestered now. It has been widely argued that GHG emissions must be reduced immediately to avoid crossing a threshold of atmospheric GHG concentration that would lead to a change of 3 degrees Celsius or more in global average temperature by the year 2105. Some argue that such a temperature change would lead to major disruptions in economies around the world (Stern et al. 2006). Therefore, any mitigation of GHG emissions that occurs many years from now may have no effect on whether or not this crucial concentration threshold is exceeded. If this is the case, C sequestration in the distant future would be relatively useless and a carbon discount rate greater than zero is justified. Alternatively, setting the annual rate of change at less than 0% (e.g. -2%) suggests that the social value of carbon sequestered in the future is greater than the value of carbon sequestered now (this is a separate issue from the value of money in the future, a dynamic accounted for by the market discount rate). This may be the case if the damage associated with climate change in the future accelerates as the concentration of GHGs in the atmosphere increases.

The value of carbon sequestration over time for a given plot x is:

In practice:

We open the program where we only have to add the data inputs: