Human exploitation of the natural world increased on an unprecedented scale in the period between the last decade of the nineteenth century and the 1960s. Within one human lifetime of “threescore and ten,” humankind experienced both escalating economic activity and a widespread depression. Viewed on a world scale, the two great wars were the most destructive of life, both of humans and of the biosphere, in history. The ecosystems of the Earth were damaged in ways unknown before, although few of the writers who commented on the fact expressed it in those terms. Rather, they talked about the depletion of natural resources. A few, like Fairfield Osborn, wondered if the cornucopia was about to run out of riches. 1
Among the forces driving exploitation was the continuing growth of human population, again unprecedented in history. From 1890 to 1960 human numbers about doubled, from 1.57 billion to 3.02 billion. The numerical increase was greatest in Asia and Europe, but these were already the most populous continents, so they grew by just under 80 percent. Population in the Americas and Oceania tripled, and in Africa (where there are few reliable statistics) probably doubled. Population increase acts as a multiplier of human impacts on other parts of the Earth, but more than simply increasing effects, it may carry them beyond critical thresholds. Renewable resources can absorb use up to a certain level, but beyond that level there are diminishing returns, and eventually exhaustion. Non-renewable resources may be exhausted.
Urbanization was a major process of change. The size and number of metropolitan areas increased, along with density of occupation. In 1890, there were only nine cities with over a million inhabitants; by 1960, sixteen cities had over four million each, and cities of over one million numbered over eighty. Such large urban concentrations occupied ever larger expanses of land, replacing natural ecosystems and agricultural acreage and reaching outward over greater distances for food and other resources. The spread of metropolitan populations and urban land uses reshaped natural landscapes and environments, altering ecosystems. Cities also affected the climate in their neighborhoods, increasing average temperature, clouds and precipitation; decreasing humidity, winds, and hours of sunshine; and adding pollution to the air and waters.
Another factor adding to human exploitation of the planet was technology. Generation of power from fossil fuels expanded in quantity and in kinds. Coal production, which had increased during the nineteenth century, passed 500 million metric tons 2 by 1890. In 1960, it reached over 2,600 million, five times as much, but was surpassed by oil, refined into petrol and diesel, and natural gas. 3 Much of the new energy was generated and transmitted in the form of electricity. In the same period, steel manufacture multiplied by 28 times. An improved internal combustion engine using petrol, light enough to be used in