The Tipping Point?

The Earth’s climate is nearing, but has not passed, a tipping point beyond which it will be impossible to avoid climate change with far-ranging undesirable consequences. These include not only the loss of the Arctic as we know it, with all that implies for wildlife and indigenous peoples, but losses on a much vaster scale due to rising seas.

Ocean levels will increase slowly at first, as losses at the fringes of Greenland and Antarctica due to accelerating ice streams are nearly balanced by increased snowfall and ice sheet thickening in the ice sheet interiors.

But as Greenland and West Antarctic ice is softened and lubricated by meltwater, and as buttressing ice shelves disappear because of a warming ocean, the balance will tip toward the rapid disintegration of ice sheets.

The Earth’s history suggests that with warming of two to three degrees, the new sea level will include not only most of the ice from Greenland and West Antarctica, but a portion of East Antarctica, raising the sea level by twenty-five meters, or eighty feet. Within a century, coastal dwellers will be faced with irregular flooding associated with storms. They will have to continually rebuild above a transient water level.

This grim scenario can be halted if the growth of greenhouse gas emissions is slowed in the first quarter of this century.

—From a presentation to the American Geophysical Union, December 6, 2005