The Azimuth Project
Ecological footprint

Definition

An ecological footprint is different from a carbon footprint.

From Wikipedia, Ecological footprint:

The ecological footprint is a measure of human demand on the Earth’s ecosystems. It compares human demand with planet Earth’s ecological capacity to regenerate. It represents the amount of biologically productive land and sea area needed to regenerate the resources a human population consumes and to absorb and render harmless the corresponding waste.

Data

Footprints for individual countries, see e.g.

An academic license for the data set from 2003 can be requested here.

Calculation

See, e.g.

Most of the following section is based on this methodology.

Global hectares

The accounting used in the above methodology relies on a few assumptions, taken from:

It is possible to keep track of most of the resources humanity consumes and the wastes humanity generates. Most of these resource and waste flows can be measured in terms of the biologically productive area necessary to maintain these flows (those resource and waste flows that cannot are excluded from the assessment). By weighting each area in proportion to its usable biomass productivity (that is, its potential production of biomass that is of economic interest to people), the different areas can be expressed in standardized hectares. These standardized hectares, which we call “global hectares,” represent hectares with biomass productivity equal to the world average productivity that year. Because these areas stand for mutually exclusive uses, and each global hectare represents the same amount of usable biomass production for a given year, they can be added up to a total representing the aggregate human demand. Nature’s supply of ecological services can also be expressed in global hectares of biologically productive space. Area demand can exceed area supply. For example, a forest harvested at twice its regeneration rate appears in our accounts at twice its area. This phenomenon is called “ecological overshoot”.

Ecological overshoot

From Global Footprint Network: Calculation methodology for the national footprint accounts, 2010 edition:

In 1961 humanity’s ecological footprint was approximately half of what the biosphere could supply. According to the 2010 Edition of the National Footprint Accounts, human demand first exceeded the planet’s biocapacity in mid 1970s. Since 1961, overall humanity’s footprint has more than doubled and overshoot has continued to increase, reaching 51% in 2007. Humanity’s ecological footprint in 2007 consisted of 22% cropland, 8% grazing land, 11% forest land, 4% fishing ground, 54% carbon uptake land, and 2% built-up land.

Formulas for footprint and biocapacity calculations

For each land use type, calculation of ecological footprint EF cEF_c (’‘c’‘ stands for consumption).

Land use types

Carbon uptake land

From Wackernagel et al, 2002 (see above):

Burning fossil fuel adds CO2 to the atmosphere. We calculate the area requirement by estimating the biologically productive area needed to sequester enough carbon emissions to avoid an increase in atmospheric CO2.

The land necessary for carbon uptake is assumed to be forest land.

EF c=P cY c(1S ocean)EQF EF_c = \frac{P_c}{Y_c} (1-S_{ocean}) \cdot EQF

with P cP_c the annual carbon emissions, S oceanS_{ocean} the fraction sequestered by the oceans (about 35%), Y cY_c the annual rate of carbon uptake per hectare of (world averaged) forest land.

However, it is important to note that the ecological footprint has a ‘’short term’‘ interpretation. Again, from Wackernagel et al, 2002:

The sequestration capacity will not remain constant in the future. For instance, changed atmospheric CO2 concentrations and global temperature may increase the eventual saturation biomass level and the rate at which that is approached. Some sequestration and oceanic absorption may even be reversed. Also, CO2 sequestration rates may decrease as more and more forest ecosystems reach maturity. Eventually afforestation will saturate so that the net rate of CO2 uptake goes to zero.

In other words, mature forests don’t accumulate additional CO2.

It should be noted that the ecological overshoot is largely due to carbon emissions. This is no surprise, because the land necessary to absorb our carbon emissions is ‘virtual’. In other words, this is the amount of land that if present, would keep atmospheric carbon dioxide concentrations from rising, at least in the short term, while forests were growing there. This is distinct from the land that provides the non-fossil resources that humanity uses.

Criticism of the concept

An article titled Does the Shoe Fit? Real versus Imagined Ecological Footprints argues that

EF measurements, as currently constructed and presented, are so misleading as to preclude their use in any serious science or policy context.

Citation: Blomqvist L, Brook BW, Ellis EC, Kareiva PM, Nordhaus T, et al. (2013) Does the Shoe Fit? Real versus Imagined Ecological Footprints. PLoS Biol 11(11): e1001700. doi:10.1371/journal.pbio.1001700

category: methodology, ecology