Ecological footprint represents

Concept

The ecological footprint is a resource-accounting measure. It converts everything a population consumes, together with the waste that must be absorbed on its behalf, into a single common unit: the amount of biologically productive land and water area needed to supply that demand on a continuing basis.

Because the unit of account is area — normally the global hectare, a hectare weighted to world-average biological productivity — a demand figure computed this way can be set directly against biocapacity, the biologically productive area actually available.

Application

The stem asks what the quantity called the ecological footprint reports. Under the definition introduced by Wackernagel and Rees and maintained by the Global Footprint Network, the accounts add up cropland, grazing land, forest land, fishing grounds, built-up land and the forest area required to absorb carbon dioxide emissions, and express that total in global hectares.

What the measure reports is therefore an area: the area of productive land and water required to meet the resource requirement of the population being measured.

Cross-check and contrast

• Energy consumption is a quantity of energy, in joules or kilowatt-hours; in footprint accounting it enters only after being converted into the productive area needed to supply that energy.

• CO2 emissions per person is a mass of carbon dioxide, in tonnes; footprint accounting converts it into the forest area needed to sequester that carbon, so it contributes a component of the total rather than being the measure.

• Forest cover is itself an area, but it records land actually under forest — a supply-side statistic belonging to biocapacity rather than to the demand a population places on nature.

Result

Therefore, the best-supported answer among the offered choices is the area of productive land and water to meet the resources requirement.