Konrad Steffen: The Global Warming Prophet

In a 2005 article in the scientific journal Climate Change, Hansen wrote that the current pace of melting, driven by the buildup of greenhouse gases in the atmosphere, could lead to a self-reinforcing and perhaps unstoppable cycle of feedback that could result in the total disintegration of the Greenland ice sheet. Hansen and many other climatologists believe that it is likely that the ice sheet will begin melting uncontrollably if global temperatures climb more than 3.6F. A rapid meltdown in Greenland would quickly raise sea levels around the world and flood coastal cities and farms. As well as sending large icebergs down the coast, the infusion of cold, fresh water could disrupt ocean currents such as the Gulf Stream, which help to keep the weather in the Northern Hemisphere regulated. "If that feedback kicks in," says Steffen, "then the average person will worry."

But because dynamic response is so poorly understood, it has not yet been incorporated into the numerical models that climatologists use to project sea-level changes. For this reason, the potential influence of dynamic response on sea-level rise wasn't factored into the sea-level projections in the "Climate Change 2007" report that the IPCC released earlier this year.

A consensus of hundreds of scientists from 130 countries, the IPCC report concludes that the warming of the climate "is unequivocal," as evidenced by rising temperatures, widespread melting of snow and ice, and rising sea levels. The report, essentially a meta-analysis of 70 climate-modeling studies, predicts a long, slow deglaciation of Greenland and West Antarctica, and a global sea-level rise of 13 to 19 feet "over a period of time ranging from centuries to millennia." By 2100, the report projects, sea levels will rise by 7 to 23 inches.

After protests by several prominent climatologists, the IPCC authors qualified their projection with a footnote acknowledging that dynamic ice-flow processes "not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming," and raise sea levels further.

"Dynamic response is the elephant in the room," says Martin Truffer of the University of Alaska's Geophysical Institute. "We know well enough that there's likely to be a higher sea-level rise than the IPCC was willing to project. They are trying to be cautious and conservative. But their conclusions lag behind the latest findings."

Over dinner, I press Steffen to make a rough prediction on sea-level rise by 2100, based on his understanding of current trends. "Unfortunately," he says, somewhat hesitantly, "I think we are looking at more like a meter."