With this melting from ice sheets and glaciers -- and the natural expansion of warmer water -- the global sea level is rising about 3 millimeters a year, 75 percent more than the average of the last century. By 2100, some climate scientists predict an increase of a little less than half a meter; others predict considerably more. In normal circumstances, a rise in the sea level of a half-meter or meter might be manageable. But during a storm surge, it could be catastrophic in low-lying areas, turning once-in-a-century floods into regular occurrences.
Arctic warming is part of an increasingly compelling case for global warming -- or, more accurately, climate disruption that seems to come from warming. Around the world we see signs large and small: tree lines moving north, the bleaching of coral in tropical waters, changes in growing seasons, the growth in population of destructive pests such as the pine beetle, the drying of southern Africa, the Mediterranean and the U.S. Southwest.
Global climate, of course, has changed before. But climate conditions for the last 10,000 years have been relatively stable, to the great benefit of civilization. Current temperature increases point beyond that band of comfort and don't seem explainable by natural cycles. The one factor dramatically different from the past is the human production of greenhouse gases, particularly the concentration of carbon dioxide in the atmosphere, which is higher than at any time in the last 800,000 years.
The challenge of replacing carbon in our economy is massive -- and many incompletely known factors, from ice dynamics to the flow of ocean currents, determine its urgency. Answers will require a politically difficult task: acting with uncertain risk.
But as I stand near the top of the world on a desolate shore with whale skulls and ruins, the crude oil economy appears about as primitive and destructive as the whale oil economy now seems.
#ThanksMichelleObama Trends on Facebook as Students Express Displeasure with School Lunch | Christine Rousselle