Figure 4.18. Percentage of non-domesticated land area projected to be under different degrees of pressure from human population and associated activities.

RIVM/UNEP (1997).
Non-domesticated land under pressure is expressed as a percentage of total regional area. Pressure is calculated for areas that are non-domesticated during the whole period 1990-2050.

Pressure categories; The following linear functions were used:
i) Population density: 0 to 100 persons per square kilometre.
The maximum pressure values for population density are derived from Hannah et al. (1994). Harrison (1992) and Terborch (1989) mentioned similar levels.
ii) Consumption and production rate: US$0 to US$6,000,000 gross national product (GNP) per square kilometre per year.
The GNP per square kilometre value is an approximation of the production and consumption rate and the related use of, and pressure on, non-domesticated areas such as emissions, extraction, physical disturbances, and fragmentation. The maximum GNP per square kilometre is similar to values found in highly populated and highly industrialized countries such as Germany and the Netherlands.
iii) Forest clearance for timber: not logged since 100 to 0 years ago.
The maximum pressure value for forest clearance for timber is set at 0 years ago, assuming total ecosystem destruction; the minimum value at 100 years, assuming no pressure and total regeneration of the forest ecosystem. Generally a longer period for forest regeneration is assumed. For example, "old growth forest" is generally defined as more than 200 years (Dudley, 1992).
iv) Climate change: a change in mean temperature of 0 degrees to 2.0 degrees Celsius within a 20-year period. For example, an increase in mean temperature of 0.2 degrees Celsius in 20 years results in a pressure rating of 1, while an increase of 2.0 degrees Celsius in 20 years results in a pressure rating of 10).
This rate is based on the still rudimentary understanding of the vulnerability of ecosystems to historical temperature changes. The maximum value of 2.0 degrees Celsius over two decades is high in comparison with the maximum temperature increase of 2.0 degrees Celsius, which is suggested as the "absolute limit beyond which the risks of grave damage to ecosystems, and of non-linear responses, are expected to increase rapidly" (Jger, 1987 and 1990).