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Bill McKibben: Remember This, 350 Parts Per Million

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  • Tim Jones
    Remember This: 350 Parts Per Million http://www.washingtonpost.com/wp-dyn/content/article/2007/12/27/AR2007122701942.html By Bill McKibben The Washington Post
    Message 1 of 1 , Dec 28, 2007
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      Remember This: 350 Parts Per Million
      By Bill McKibben
      The Washington Post
      Friday 28 December 2007 Page A21

      This month may have been the most important yet in the two-decade
      history of the fight against global warming. Al Gore got his Nobel in
      Stockholm; international negotiators made real progress on a treaty
      in Bali; and in Washington, Congress actually worked up the nerve to
      raise gas mileage standards for cars.

      But what may turn out to be the most crucial development went
      largely unnoticed. It happened at an academic conclave in San
      Francisco. A NASA scientist named James Hansen offered a simple,
      straightforward and mind-blowing bottom line for the planet: 350, as
      in parts per million carbon dioxide in the atmosphere. It's a number
      that may make what happened in Washington and Bali seem quaint and
      nearly irrelevant. It's the number that may define our future.

      To understand what it means, you need a little background.

      Twenty years ago, Hansen kicked off this issue by testifying
      before Congress that the planet was warming and that people were the
      cause. At the time, we could only guess how much warming it would
      take to put us in real danger. Since the pre-Industrial Revolution
      concentration of carbon in the atmosphere was roughly 275 parts per
      million, scientists and policymakers focused on what would happen if
      that number doubled - 550 was a crude and mythical red line, but
      politicians and economists set about trying to see if we could stop
      short of that point. The answer was: not easily, but it could be done.

      In the past five years, though, scientists began to worry that
      the planet was reacting more quickly than they had expected to the
      relatively small temperature increases we've already seen. The rapid
      melt of most glacial systems, for instance, convinced many that 450
      parts per million was a more prudent target. That's what the European
      Union and many of the big environmental groups have been proposing in
      recent years, and the economic modeling makes clear that achieving it
      is still possible, though the chances diminish with every new
      coal-fired power plant.

      But the data just keep getting worse. The news this fall that
      Arctic sea ice was melting at an off-the-charts pace and data from
      Greenland suggesting that its giant ice sheet was starting to slide
      into the ocean make even 450 look too high. Consider: We're already
      at 383 parts per million, and it's knocking the planet off kilter in
      substantial ways. So, what does that mean?

      It means, Hansen says, that we've gone too far. "The evidence
      indicates we've aimed too high - that the safe upper limit for
      atmospheric CO2is no more than 350 ppm," he said after his
      presentation. Hansen has reams of paleo-climatic data to support his
      statements (as do other scientists who presented papers at the
      American Geophysical Union conference in San Francisco this month).
      The last time the Earth warmed two or three degrees Celsius - which
      is what 450 parts per million implies - sea levels rose by tens of
      meters, something that would shake the foundations of the human
      enterprise should it happen again.

      And we're already past 350. Does that mean we're doomed? Not
      quite. Not any more than your doctor telling you that your
      cholesterol is way too high means the game is over. Much like the way
      your body will thin its blood if you give up cheese fries, so the
      Earth naturally gets rid of some of its CO2each year. We just need to
      stop putting more in and, over time, the number will fall, perhaps
      fast enough to avert the worst damage.

      That "just," of course, hides the biggest political and economic
      task we've ever faced: weaning ourselves from coal, gas and oil. The
      difference between 550 and 350 is that the weaning has to happen now,
      and everywhere. No more passing the buck. The gentle measures bandied
      about at Bali, themselves way too much for the Bush administration,
      don't come close. Hansen called for an immediate ban on new
      coal-fired power plants that don't capture carbon, the phaseout of
      old coal-fired generators, and a tax on carbon high enough to make
      sure that we leave tar sands and oil shale in the ground. To use the
      medical analogy, we're not talking statins to drop your cholesterol;
      we're talking huge changes in every aspect of your daily life.

      Maybe too huge. The problems of global equity alone may be too
      much - the Chinese aren't going to stop burning coal unless we give
      them some other way to pull people out of poverty. And we simply may
      have waited too long.

      But at least we're homing in on the right number. Three hundred
      and fifty is the number every person needs to know.

      Bill McKibben is a scholar in residence in environmental studies
      at Middlebury College and the author of the forthcoming "Bill
      McKibben Reader."
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