Save polar bears one electric car at a time: Column

• The ice-free period during which polar bears must fast has increased by nearly a day per year.
• When will we require the greenhouse gas reductions necessary to stop the long-term sea ice decline%3F
• Polar bears could be absent from the Churchill area by the middle of this century.

Each year in early November polar bears gather on the tundra near Churchill, Manitoba, as they wait for the autumn freeze. The bears are eager to return to the sea ice where they can resume catching seals, their favored prey, and break their summer-long fast. I'm eager as well for more enlightened public policies that better protect polar bears and our planet.

Over the past three decades, the ice-free period during which polar bears must fast has increased by nearly a day per year. But natural variation could make this year's freeze-up later or earlier than the long-term trend would predict.

Standing on the back deck of a Tundra Buggy, I blow into my gloves, and pull my hood up tight, as I watch a big male bear gazing into the gray waters of Hudson Bay. I imagine he is asking himself when this year's freeze will occur. I, on the other hand, am wondering when our leaders in Washington, D.C., will require the greenhouse gas reductions necessary to stop the long-term sea ice decline and save the species.

In 2007, my colleagues and I predicted that polar bears could be absent from the Churchill area by the middle of this century. That prediction led to polar bears becoming the first species listed as threatened under the U.S. Endangered Species Act because of threats from man-caused global warming. In 2010, we published a follow-up paper showing that preventing the demise of polar bears is all about reducing our use of fossil fuels and halting the rise in global temperatures.

Past efforts to protect threatened species included "on the ground" measures such as fighting poachers, establishing refuges or building fences. We cannot, however, build a fence to protect the sea ice from rising temperatures. Polar bear conservation cannot be done in the Arctic. Anthropogenic global warming is indeed the leading conservation challenge of our time.

A few weeks ago, the hundreds of scientists composing the Intergovernmental Panel on Climate Change (IPCC) issued their fifth assessment report, emphasizing that global warming is far more than a conservation challenge. It threatens our economies, our social structures, and indeed human existence as we have known it.

Our society's reliance on fossil fuels is unsustainable, and is maintained only because we are hiding the true costs of releasing CO2 and deferring payment to future generations. Policies requiring we pay the true costs of using ancient carbon to power today's world, would level the playing field, making renewable energy and other sustainable practices more competitive. The resulting competition would, in turn, stimulate our ingenuity, create jobs, and preserve a climate that will support polar bears and the rest of us.

The good news is that we can solve this problem and head off the worst impacts from artificially warming the world. But for each year we delay action, the challenges become more daunting.

Steven C. Amstrup is chief scientist with Polar Bears International and the 2012 Indianapolis Prize Winner for his work in animal conservation.