Land and freedom
The human transformation of land has been extremely good news for our species overall, allowing a population now approaching 7 billion people to be supported at ever-rising standards of living and comfort. Each of us now lives like a medieval king, offered choices of sumptuous foods from around the globe and surrounded by machines that wash our clothes and dishes at the touch of a button.
But, for land in particular, our impacts on the planet’s terrestrial surface are now so extensive and transformative that they threaten the capacity of varied ecosystems to self-regulate and maintain the living biosphere overall. Natural landscapes filter water, produce oxygen, sequester carbon, and provide vital habitat for other species. Whether these landscapes harbour forests, wetlands, grasslands or even deserts, the planet’s varied biomes are an integral part of the Earth system – and are essential to its continued sustainable functioning.
Computer models of the Earth system can demonstrate how varied ecological zones are important to the planet overall. In one modelling study, climatologist Peter Snyder and his colleagues tried deleting entire biomes from their simulated planet to see what then happened to the climate. Remove the savannahs, they found, and you reduce rainfall totals by a third. Press the delete key over the tropical forests, and entire continents see dramatic reductions in their precipitation and sudden rises in temperature. Different biomes, from temperate forests to the Arctic tundra, likely have significant effects on winds, temperatures and atmospheric circulation patterns.
As more and more of the Earth’s surface sees these traditional biological zones transformed into ‘anthropogenic biomes’ dominated by humans, Earth-system scientists expect the planet’s functioning to become steadily more unstable. Across at least three-quarters of the world today, humans are as or more important in determining which species make up the ecosystem than previously dominant factors like latitude, climate and geography. Instead of the neat green and yellow strips that we learned about in geography class, denoting jungle, desert and so on, the planet is now divided into a complex mosaic of different human-influenced ecosystems. Human capture of the planet’s productive capacity, according to the most recent relevant study, now adds up to about 24 per cent of the total productivity of the Earth’s terrestrial biosphere. In other words, a quarter of everything produced by all plants on land is eaten or otherwise consumed by us.
Different landscapes are exploited with different intensity: whilst forests will yield up to a fifth of their annual production in fuel, fibre or timber, cropland allows us to grab an impressive 83 per cent of the yearly productive share per hectare. The human species, therefore, whilst comprising only half of 1 per cent of the global animal biomass, consumes a significant fraction of everything the Earth produces. This triumph for us is of course a disaster for the species we have displaced from their food webs: the disappearance of habitat and food supply is currently the greatest cause of the planet’s continuing loss of biological diversity. It is also clear that ecological tipping points can be crossed if we push this process too far, with potentially irreversible consequences as overgrazed grassland tips into desert, or as degraded tropical forest dries out and burns over vast areas of Indonesia and Brazil.