Environmental footprinting

Environmental footprinting is a way of measuring the impact of humans on the Earth's biosphere (the natural environment). It looks at the flow rates of food, fibre, and wood used by humans, and of carbon dioxide (CO2) produced by humans. It then compares them to the flow rates that the biosphere can supply (or absorb, in the case of CO2).

The flow rates are expressed in terms of land area: eg., a hectare (ha) of wheat field can produce so many kilograms of wheat per year; a hectare of tropical rainforest can absorb so many kilograms of CO2 per year; etc. The land area required to produce and absorb our flows is called our ecological footprint (or environmental footprint). The biologically productive land area of the Earth is called the biocapacity. It includes most of the Earth's surface area exclusive of deep oceans, deserts, and polar icecaps, and was estimated to be 11.9 billion hectares in 2007. (The total surface area of the Earth is 51 billion hectares.)

A striking result of ecological footprinting is that our ecological footprint is at present about one and a half times the bioproductive land area of planet Earth. This phenomenon is called `overshoot'. Its principal results are that we are depleting timber stocks and accumulating CO2 in the atmosphere. (We presently produce CO2 about two times faster than the Earth's oceans and land vegetation absorb it. )

Methodology
In the footprinting methodology, bioproductive land is divided into six broad categories: crop land, grazing land, forests that provide timber and fuel wood, forests that sequester CO2, fishing grounds, and built-up areas. Actual land and water areas can be scaled according to their bioproductivity so that they are expressed in a common unit called the global hectare (gha). For instance, there are 1.6 billion actual hectares of crop land on Earth, but they count as 3.9 billion global hectares because crop land is unusually bioproductive. By contrast, there are 3.4 billion hectares of grazing land but they only count as 1.8 billion global hectares. Local differences in per-hectare yield and in efficiency of production methods can be accomodated by this method.

In the methodology, a piece of land can only be counted in one category. It might be supposed that a forest that produces timber and fuel could also provide carbon uptake, but this is not the case, because timber harvest leads to release of the stocked carbon.

Other results
The 18 billion hectare ecological footprint of the human race in 2007 was, in per capita terms 2.7 hectares per person. In other words, the average person requires 2.7 hectares of land exclusively devoted to the provision of her food, fibre, and wood consumption and the uptake of her CO2 production. The bioproductive land area of the Earth is 1.8 hectares per person (based on a 2007 population of 6.7 billion). This is the size of the `personal planetoid' available to each of us if we are to be sustainable. However, it is also estimated that if the extinction rate of wild species is to be normalised, four fifths of the Earth's bioproductive area must be left unmodified by human beings, as wild habitat. Even if carbon-sequestration forest can do double duty as wild habitat, this reduces the personal planetoid to about 0.72 hectares.'). Because of their high consumption, people in the wealthy countries have much higher than average ecological footprints. The average person in the United States has a footprint of 8.0 hectares; in France, 5.0 ha; in China, 2.2 ha; in the lowest income countries (combined population 1.3 billion), 1.2 ha; in one of them, Bangladesh, 0.62 ha (all 2007 data). Carbon sequestration is, by a considerable margin, the largest of the human demands placed on the biosphere. It accounts for 54% of the global ecological footprint. As of 2007 it takes 0.8 Earths to sequester humanity's CO2 emissions. The carbon demand is also the fastest-growing of the demands; in 1961 it was only about 0.08 Earths, out of a total ecological footprint then of 0.6 Earths. The ecological footprint methodology does not account for all human demands on the environment. This is acknowledged by its authors. It does not track wastes other than CO2. It tracks only renewable resources. Regarding non-renewable resources such as fossil fuels and metal ores, it tracks their carbon-emissions impact but not their stocks or other parameters. Also notably, it lacks a fresh water account; it has nothing to say about the use or contamination of water. It does not directly measure the state of the soil or soil erosion, although this will show up in its accounts down the road as a reduced ratio of biocapacity to footprint. To recapitulate this paragraph: the ecological footprint is an underestimate of human impact.

Praxis
The ecological footprint concept was created by William Rees and Mathis Wackernagel at the University of British Columbia, Canada, in the early 1990s. The Global Footprint Network, headed by Wackernagel, updates the calculations annually; proposes standards to try to keep the methodology consistent, `accurate and transparent'; and promotes the footprint idea. It uses about 6,000 data per country in its calculations; the main sources of these data include UN FAOSTAT, UN COMTRADE, and OECD International Energy Agency. The governments of Wales, Switzerland, and Japan; Sonoma County, California, USA; and the World Wildlife Federation have used ecological footprinting.

A hectare is equal to 2.47 acres, and is about the size of a soccer field.