Two major new studies, in Nature and Science, sharply increase the projected sea-level rise (SLR) by 2100. This post discusses the Science study ($ub. req’d), “Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise,” which concludes:

On the basis of calculations presented here, we suggest that an improved estimate of the range of SLR to 2100 including increased ice dynamics lies between 0.8 and 2.0 m.

… these values give a context and starting point for refinements in SLR forecasts on the basis of clearly defined assumptions and offer a more plausible range of estimates than those neglecting the dominant ice dynamics term.

Scientific analysis is finally catching up to scientific observation. In 2001, the IPCC projected that neither Greenland nor Antarctica would lose significant mass by 2100. The IPCC made the same basic projection again in 2007. Yet both ice sheets already are. As Penn State climatologist Richard Alley said in March 2006, the ice sheets appear to be shrinking “100 years ahead of schedule.”

So for over a year now, delayers like Bjørn Lomborg have been able to cling to (a misrepresentation of) the IPCC’s lowball SLR estimate. Science‘s Richard Kerr explained what the IPCC did wrong and what the new study does right:

Warming glaciers raise sea level in two main ways. They add more water as they melt, and they also add water when ice breaks off from glacial flows. The incidence of this latter phenomenon has soared in recent years for some glaciers draining the southern Greenland Ice Sheet, much to the mystification of glaciologists. Unable to model such accelerated ice losses, members of the Intergovernmental Panel on Climate Change declined to include them in their widely cited projection of up to 60 centimeters of sea level rise by 2100.

Glaciologist W. Tad Pfeffer of the University of Colorado, Boulder, and his colleagues tackled glacier flow anyway. They calculated how fast glaciers would have to flow in order to raise sea level by a given number of meters and then considered whether those flow rates were plausible or even physically possible.

Needless to say, a sea-level rise of one meter by 2100 would be an unmitigated catastrophe for the planet, even if sea levels didn’t keep rising several inches a decade for centuries, which they inevitably would. The first meter of SLR would flood 17 percent of Bangladesh [PDF], displacing tens of millions of people, and reducing its rice-farming land by 50 percent. Globally, it would create more than 100 million environmental refugees and inundate over 13,000 square miles of this country [PDF]. Southern Louisiana and South Florida would inevitably be abandoned, especially in the face of a steadily increasing number of killer super-hurricanes.

These results should come as no surprise to anybody but deniers and delayers. The scientific literature has been moving in this direction for a couple of years now — too late for the IPCC to consider in its latest assessment. For instance, an important Science article from 2007 [PDF] used empirical data from last century to project that sea levels could be up to 5 feet higher in 2100 and rising 6 inches a decade! Another 2007 study from Nature Geoscience came to the same conclusion. Leading experts in the field have a similar view.

Since delayers like to hide behind the IPCC’s 2007 sea-level estimate — even though they really don’t believe most of what the IPCC says or most of the scientific literature on which it bases its conclusion — you’re going to be hearing the IPCC estimate for another several years, until the IPCC does a new report and puts in a more realistic estimate. That said, while the delayers never acknowledge it, even the 2007 IPCC report “was the first to acknowledge that the melting of the Greenland ice sheet from rising temperature [which would raise the oceans 23 feet] could result in sea-level rise over centuries rather than millennia,” as The New York Times put it.

"Part 2" looks at new paleoclimate research on how fast Greenland could shed ice.

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.