Wednesday, October 28, 2009

Human Impact - Are We Causing our Own Extinction

Our Inferences about life in the past are based on fossil remains suggesting that species expand in number and complexity and then are suddenly reduced through successive spams of extinction. Scientist have identified 5 major extinctions in the past 550 million years and each has taken approximately 10 million years of natural evolution to restore.

We are fortunate to have evolved when biological diversity has been at the greatest level ever achieved. Succeeding human generations will not be as fortunate: the current extinction crisis is without precedent - never before has a single species been responsible for such a massive loss of diversity. In essence, humans are the catalyst driving the earth's sixth major extinction event.

I find the following illustration a great example of the unprecedented rate and scale of human activity is graphically illustrated by Alan Thein Durning in his paper "Saving the Forests: What Will It Take?"

Imagine a time-lapse film of the Earth taken from space. Play back the last 10,000 years sped up so that a millennium passes every minute. For more then seven of the ten minutes, the screen displays what looks like a still photograph: the blue planet Earth, its lands swathed in a mantle of trees. Forests cover 34 percent of the land. Aside from the occasional flash of a wildfire, none of the natural changes in hte forest coat are perceptible. The Agricultural Revolution that transforms human existence in the film's first minute is invisible.

After seven and a half minutes, the lands around Athens and the tiny Islands of the Aegean Sea lose their froest. This is the flowering of Classical Greece. Little else changes. at nine minutes - 1,000 years ago - the mantle grows threadbare in scatered parts of Europ, Central America, China, and India. then 12 Seconds from the end, one century ago Eastern North America is deforested. This is the Industrial Revolution. Little else appears to have changed. Forest covers 32 percent of the land.

In the last three seconds - after 1950 - the change accelerates explosively. Vast tracts of forest vanish from Japan, the Philippines, and the mainland of Southeast Asia, from most of Central America and the horn of Africa, from Western North America and Eastern South America, fron the Indian subcontinent and sub-Saharan Africa. fires rage in the Amazon basin where they never did before, set by ranchers and peasants. Central Europe's forests die, posoned by the air and rain. Southeast Asia resembles a fod with mange. Malaysian Borneo appears shaved. In the final fractions of a second the clearing spreads to Siberia and the Canadian North. Forest disappear so suddenly from so many places that looks like a plague of locusts has descended on the planet.

The film on the last frame. Trees cover 26 percent of the land. Three-fourths of the original forest area still bears some tree cover. But just 12 percent of the Earth's surface - one third of the initial total - consists of intact forest ecosystems. the rest holds biologically impoverished stnad of commercial timber and fragmented regrowth. This is the present: a globe profoundly altered by the workings - or failings - of the human economy.

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