From Envirowiki

A global hectare is a measurement defining an area of global average productivity. It is becoming more frequently used in geographic, environmental, and sociological circles, as it relates both to ecological footprint, and global development.

The global hectare is a measurement of biocapacity of the entire earth - one global hectare is a measurement of the average biocapacity of all hectare measurements any biologically productive areas on the planet. If you take the sum of the world's biocapacity, then divide it by the number hectares on the earth's surface, you get the biocapacity of one average earth hectare. this is a global hectare.

Global hectares vary from place to place. ie. in a lush area with high rainfall, a global hectare would be much smaller than in a semi-arid area, where the required area for the same biomass would be much larger, as it's harder for life to thrive there.

[edit] 1 uses

the Global Hectare is a useful measure of biocapacity, as is can convert things like Human dietary requirements into a physical area, and this can be used to show how many people a certain region of the earth can sustain with current technologies and agricultural methods.

[edit] 2 problems

The Global Hectare measurement is fundamentally an anthropocentric measurement, in that it considers the world's biological resources in terms of human food production. This basically means that it takes no care for other species - global hectares could work on the idea that all the world's surface could be biologically productive for humans, thus leaving no space for other species. Obviously, this system would crash due to monoculture problems. For this to be overcome, an arbitrary percentage of the earth's land mass must be decided as ethically or morally usable. Such a percentage can never be right, or correct, only good enough.

[edit] 3 sources

• Global Footprint Network Glossary.
• What is a global hectare (gha)? - Ecological Budget UK