The Human Population Explosion

baloney_detector · 03-19-2007, 11:12 AM

Out of House and Home

by Peter Tyson

Can what happened on one small island in the South Pacific serve as a cautionary tale for the entire planet?

To see just how clearly a growing human population relies on and impacts its natural environment, one need look no farther than Easter Island, the South Pacific isle with the famous stone statues known as moai. I have been doing a lot of reading about the fate of Easter in preparation for an upcoming trip, and, as the geographer John Flenley and archeologist Paul Bahn write in The Enigmas of Easter Island, "it is a story with an urgent and sobering message for our own times."

Easter Island is the most isolated piece of inhabited land in the world. A speck of volcanic rock only about twice the size of Manhattan, it lies roughly 2,250 miles northwest of Chile and 1,300 miles east of Pitcairn Island (of Mutiny on the Bounty fame). When, as most scholars believe, the first Polynesian settlers arrived from the west about the middle of the first millennium A.D., they found a pristine tropical island. Covered in a palm forest, it resounded with the cries of 25 or more species of nesting seabirds and at least six land birds. Though its soils were low in nutrients, the island bore a wide coastal plain well suited for cultivation of the taro, yam, sweet potato, and other crops these pioneers brought with them and which became their staples.

The population grew slowly at first, then more quickly, reaching a peak around the middle of the second millennium A.D. of anywhere from 10,000 to 20,000 people. By this time, the Rapanui, as the islanders are known, had developed a complex society of chiefdoms and elaborate stone architecture epitomized by the moai. Beginning around 1600, however, Rapanui civilization began to fall apart, and by the mid-19th century, it had all but disappeared.

After decades of painstaking work, a host of archeologists, ethnographers, and other specialists have painted a comprehensive picture of what transpired on Easter Island. And the parallels between what happened there and what is occurring today in the world at large—albeit more slowly and on a much vaster scale—are, as the evolutionary biologist Jared Diamond has put it, "chillingly obvious."

NOVA | World in the Balance | Out of House and Home | PBS

baloney_detector · 03-19-2007, 12:02 PM

The Scale of Our Presence

(From the American Association for the Advancement of Science’s Atlas of Population and Environment.)

“Humans are perhaps the most successful species in the history of life on Earth. From a few thousand individuals some 200 000 years ago, we passed 1 billion around 1800 and 6 billion in 1999. Our levels of consumption and the scope of our technologies have grown in parallel with, and in some ways outpaced, our numbers.

But our success is showing signs of overreaching itself, of threatening the key resources on which we depend. Today our impact on the planet has reached a truly massive scale. In many fields our ecological "footprint" outweighs the impact of all other living species combined.

We have transformed approximately half the land on Earth for our own uses -- around 11 percent each for farming and forestry, and 26 percent for pasture, with at least another 2 to 3 percent for housing, industry, services and transport [1]. The area used for growing crops has increased by almost six times since 1700, mainly at the expense of forest and woodland [2].

Of the easily accessible freshwater we already use more than half. We have regulated the flow of around two thirds of all rivers on Earth, creating artificial lakes and altering the ecology of existing lakes and estuaries [3].

The oceans make up seven tenths of the planet's surface, and we use only an estimated 8 percent of their total primary productivity. Yet we have fished up to the limits or beyond of two thirds of marine fisheries and altered the ecology of a vast range of marine species. During this century we have destroyed perhaps half of all coastal mangrove forests and irrevocably degraded 10 percent of coral reefs.

Through fossil-fuel burning and fertilizer application we have altered the natural cycles of carbon and nitrogen. The amount of nitrogen entering the cycle has more than doubled over the last century, and we now contribute 50 percent more to the nitrogen cycle than all natural sources combined. The excess is leading to the impoverishment of forest soils and forest death, and at sea to the development of toxic algal blooms and expanding "dead" zones devoid of oxygen [4].

By burning fossil fuels in which carbon was locked up hundreds of millions of years ago, we have increased the carbon dioxide content of the atmosphere by 30 percent over pre-industrial levels. We have boosted methane content by 145 percent over natural levels [5].

Through mining and processing we are releasing toxic metals into the biosphere that would otherwise have remained safely locked in stone. We are producing new synthetic chemicals, many of which may have as yet undetermined effects on other organisms.

We have thinned the ozone layer that protects life on Earth from harmful ultra-violet radiation. Most scientists agree that human activities are contributing to global warming, raising global temperatures and sea levels.

These processes affect the habitats and environmental pressures under which all species exist. As a result, we have had an incalculable effect on the Earth's biodiversity. The 484 animal and 654 plant species recorded as extinct since 1600 are only the tip of a massive iceberg [6].

We have become a major force of evolution, not just for the "new" species we breed and genetically engineer, but for the thousands of species whose habitats we modify, consigning many to extinction; compelling others to evolve and adapt to our pressures. We have become a force of nature comparable to volcanoes or to cyclical variations in the Earth's orbit.

The scale of our activities depends on our population numbers, our consumption and the resource or pollution impact of our technologies -- and all three of these factors are still on the increase. The maps on the previous pages illustrate the increasing spread and density of the human population over the last three centuries.

As we enter the third millennium, the destiny of the planet is in our hands as never before, yet they are inexperienced hands. We are modifying ecosystems and global systems faster than we can understand the changes and prepare responses to them. All the factors in this vast equation affect each other constantly. In a globalized world the elements of human activity interact with each other and with local and planetary environments.

In this unprecedented situation, the need to be fully aware of what we are doing has never been greater. We need to understand the way in which population, consumption and technology create their impact, to review that impact across the most critical fields, and to find ways of using our understanding of the links to inform policy.”

AAAS Atlas of Population and Environment

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode