The global hectare (gha) is a measurement unit for the
ecological footprint
The ecological footprint measures human demand on natural capital, i.e. the quantity of nature it takes to support people and their economies. It tracks human demand on nature through an ecological accounting system. The accounts contrast the biolo ...
of people or activities and the
biocapacity
The biocapacity or biological capacity of an ecosystem is an estimate of its production of certain biological materials such as natural resources, and its absorption and filtering of other materials such as carbon dioxide from the atmosphere.
Bio ...
of the
Earth
Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
or its regions. One global hectare is the world's annual amount of biological production for human use and human waste assimilation, per hectare of biologically productive land and fisheries.
It measures production and consumption of different products. It starts with the total biological production and waste assimilation in the world, including crops, forests (both wood production and CO
2 absorption), grazing and fishing.
The total of these kinds of production, weighted by the richness of the land they use,
is divided by the number of hectares used. Biologically productive areas include cropland, forest and fishing grounds, and do not include deserts, glaciers and the open ocean.
"Global hectares per person" refers to the amount of production and waste assimilation per person on the planet. In 2012 there were approximately 12.2 billion global hectares of production and waste assimilation, averaging 1.7 global hectares per person.
Consumption totaled 20.1 billion global hectares or 2.8 global hectares per person, meaning about 65% more was consumed than produced. This is possible because there are natural reserves all around the globe that function as backup food, material and energy supplies, although only for a relatively short period of time. Due to overconsumption, these reserves are being depleted at an ever increasing tempo (see
Earth Overshoot Day).
The term "global hectare" was introduced in the early 2000s, based on a similar concept from the 1970s named "ghost acreage".
[Mathis Wackernagel, William Rees, ''Our Ecological Footprint: Reducing Human Impact on the Earth'' (1998), p. 49.]
Opponents and defenders of the concept have discussed its strengths and weaknesses.
Applications
The global hectare is a useful measure of biocapacity as it can convert things like
human dietary requirements into common units, which can show how many
people
The term "the people" refers to the public or Common people, common mass of people of a polity. As such it is a concept of human rights law, international law as well as constitutional law, particularly used for claims of popular sovereignty. I ...
a certain region on earth can sustain, assuming current
technologies
Technology is the application of Conceptual model, conceptual knowledge to achieve practical goals, especially in a reproducible way. The word ''technology'' can also mean the products resulting from such efforts, including both tangible too ...
and
agricultural
Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created f ...
methods. It can be used as a way of determining the relative
carrying capacity
The carrying capacity of an ecosystem is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as the ...
of the earth.
Different hectares of land can provide different amounts of global hectares. For example, a hectare of lush area with high
rainfall
Rain is a form of precipitation where water droplets that have condensed from atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. ...
would scale higher in global hectares than would a hectare of desert.
It can also be used to show that consuming different foods may increase the earth's ability to support larger populations. To illustrate,
producing meat generally requires more land and energy than what producing vegetables requires; sustaining a meat-based diet would require a less populated planet.
Hectare equivalents
On average, a global hectare can be produced in the area of a standard hectare. A
hectare
The hectare (; SI symbol: ha) is a non-SI metric unit of area equal to a square with 100-metre sides (1 hm2), that is, square metres (), and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. ...
(; symbol ha) is a unit of area equal to (a square 100 metres on each side or 328 feet on each side), 2.471 acres, 0.01 square kilometers, 0.00386102 square miles, or one square
hectometre
The hectometre, ( SI symbol: hm), spelt hectometer in American and Philippine English, is a unit of length in the International System of Units (SI), equal to one hundred metres and to one tenth of a kilometre. The word comes from a combination ...
(100 metres squared).
See also
References
{{reflist
Ecology