Generations from now, long after the last Twitter follower has unfriended the last Facebook user, this decade will be remembered and felt for its impact on Nature: the species that were saved and those that were lost; the heating of the planet; the forests cut down and those that remain to provide oxygen to our children’s children, and the first halting steps toward a clean energy future.

By those standards, this decade has been one of great beginnings, tragic ends, and the uplifting possibility of a new relationship between man and Nature.

To be sure, these were years of fire and devastation:  

In the last decade, more than 200 million acres of rainforest have been cleared and burned, sending an amount of pollution into the atmosphere equivalent to seven times the United States’ annual emissions. It’s as if all the vegetation in the states of Montana, Colorado, and New York combined had been torched.

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The burning of coal, oil, and forests has added more than 250 billion tons of carbon dioxide to the atmosphere, helping make this decade the hottest on record — with corresponding increases in desertification, drought, and extreme weather events such as Hurricane Katrina.

To me, however, the saddest symbol of what has happened to Nature during this decade is the fate of the baiji, the white river dolphin found only in China’s Yangtze River. The baiji was a playful animal that dined on the Yangtze’s once plentiful fish and was traditionally venerated by the region’s people. Hunting and overfishing caused a drastic decline in the baiji’s population, and there were only a few hundred survivors at the beginning of the decade.

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Then China, in its thirst for energy, completed its notorious Three Gorges Dam, and the fate of the baiji was sealed. The dam caused a build-up of pollution and a further reduction in fish populations that doomed the baiji. The species was declared “functionally extinct” in 2007 when an expedition failed to spot a single living baiji. The baiji became the first whale or dolphin in history to be killed off by human activity. The world will always be a little bereft without it.

But this decade also saw some tentative first steps toward a true balance between Nature and humanity.

The United States government protected more than 50 million acres of old growth forest from logging. It also declared an area the size of Spain off limits to fishing in an effort to preserve the ocean for future generations.

Recognition of the consequences of burning fossil fuels for energy has led to extraordinary growth in clean energy alternatives: more than 15 times the amount of solar energy is generated today than was generated in 2000, with much greater growth projected for the future.

Of course, these flashes of progress are nowhere near enough — yet — to make up for the immense damage being wrought by a growing population with higher and higher consumption levels.

But what can give us hope going into 2010 is the environmental revolution of the mind: the widespread realization that protecting the environment is the path, not the obstacle to prosperity. During the 2008 U.S. presidential campaign, when candidates talked about creating jobs, they more often than not did it against a backdrop of wind turbines.

The culmination of this decade’s green revolution was to have been the passage of energy and climate legislation in the United States and the completion of a binding international agreement in Copenhagen. Both would accomplish something extraordinary: finally tying the universal human quest for a better life to protection of the Earth’s natural resources, not their destruction.

That new way of life hasn’t been realized — yet. But despite the damage done to our planet in these last ten years, the first decade of the 21st century may one day be seen as the wellspring of its salvation.