Christopher Flavin

Over the past half-million years, the world's climate has seen four ice ages and four warm periods separating them, with extensive glaciers engulfing large swaths of North America, Europe, and Asia and then retreating, thousands of species displaced, and the shape of coastlines rearranged as sea levels rose and fell. Yet throughout these hundreds of thousands of years, the atmospheric concentration of carbon dioxide (CO2), which plays a key role in regulating the climate, has never risen above 300 parts per million.1

In 2007, the atmospheric concentration of CO2 passed 382 parts per million—and it is already at the equivalent of 430 parts per million if the effect of other greenhouse gases is included. (See Figure 6-1.) Humanity is at risk of creating a climate unlike any seen before—unfolding at an unnatural, accelerated pace—more dramatic than any changes in the climate since Earth was last struck by a large asteroid nearly a million years ago. Unless greenhouse gas emissions begin to decline within the next decade, we risk triggering a runaway disruption of the world's cli mate, one that could last centuries and that our descendants would be powerless to stop.2

The world is entering uncharted territory. Fossil fuels made the modern economy and all of its material accomplishments possible. But building a low-carbon economy is now the central challenge of our age. Meeting that challenge will require restructuring the global energy industry through technological, economic, and policy innovations that are as unprecedented as the climate change it must address.

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