The current threats

Abstract

In the 12,000 years or so since agriculture was first invented, our own species Homo sapiens sapiens has seized control of the world. The extra food from agriculture has allowed a huge increase in human population, and the need to grow crops, keep farm animals, and build homes gave our ancestors reason to alter the land surface wherever they went. Now there are more than 6.7 billion of us in the world— nearly a thousand times as many as there were before farming. As a species we have reached such levels of abundance and technological sophistication that we are now altering the basic properties of the Earth’s system. A large proportion of the world’s vegetation cover has been changed: forests have been cleared away, and much of the natural grassland and scrub has been ploughed up. The transformation began on a large scale in the temperate zones of the Middle East, Europe, Asia, and then North America and Australia, after which it moved to the tropics. At present, somewhere around 6 million hectares of tropical forest—an area about the size of the state of Delaware in the U.S., or Wales in the U.K.—are being lost each year (FAO, 2005; Achard et al., 2008). Such changes in the world’s vegetation caused by humans are in themselves enough to have far-reaching effects on the climate system. There are good theoretical reasons for thinking that the forest loss that has already occurred must already have altered patterns of temperature and rainfall. There are observations of particular areas both “before” and “after” deforestation that seem to validate this (see my other book Vegetation-Climate Interaction, Adams, 1997, for more on this topic).