10.2 The industrialization of nature: a modern history (1500 to  (Page 4/9)

It has been estimated that industrial fertilizers have increased the planet’s human carrying capacity by two billion people. Unfortunately, most of the chemical fertilizer applied to soils does not nourish the crop as intended, but rather enters the hydrological system, polluting aquifers, streams, and ultimately the oceans with an oversupply of nutrients, and ultimately draining the oxygen necessary to support aquatic life. As for the impact of fertilizers on soil productivity, this diminishes over time, requiring the application of ever greater quantities in order to maintain yields.

Deforestation

Arguably the biggest losers from 20 ^th century economic growth were the forests of the world’s tropical regions and their non-human inhabitants. Across Africa, Asia, and the Americas, approximately one-third of forest cover has been lost. Because about half of the world’s species inhabits tropical rainforests, these clearances have had a devastating impact on biodiversity    , with extinction    rates now greater than they have been since the end of the dinosaur era, 65 million years ago. Much of the cleared land was converted to agriculture, so that the amount of irrigated soils increased fivefold over the century, from 50 to 250m hectares. Fully 40% of the terrestrial earth’s total organic output is currently committed to human use. But we are now reaching the ceiling of productive land expansion, in terms of sheer area, while the continued productivity of arable land is threatened by salinity, acidity and toxic metal levels that have now degraded soils across one third of the earth’s surface, some of them irreversibly.

Wetlands drainage and damming

Meanwhile, the worlds’ vital wetlands, until recently viewed as useless swamps, have been ruthlessly drained—15% worldwide, but over half in Europe and North America. The draining of wetlands has gone hand in hand with large-scale hydro-engineering projects that proliferated through the last century, such that now some two-thirds of the world’s fresh water passes through dam systems, while rivers have been blocked, channeled, and re-routed to provide energy, irrigation for farming, and water for urban development. The long-term impacts of these projects were rarely considered in the planning stages, and collectively they constitute a wholesale re-engineering of the planet’s hydrological system in ways that will be difficult to adapt to the population growth demands and changing climatic conditions of the 21 ^st century. As for the world’s oceans, these increasingly show signs of acidification due to carbon emissions, threatening the aquatic food chain and fish stocks for human consumption, while on the surface, the oceans now serve as a global conveyor belt for colossal amounts of non-degradable plastic debris.