NSF Study: Fastest Sea-Level Rise in Two Millennia Linked to Increasing Global Temperatures

New research “points toward projected sea level rise lying at or near the upper range of current projections, more than a meter [100 cm, 39 inches] by the end of this century under business-as-usual carbon emissions,” says co-author Michael Mann.

The National Science Foundation news release for the study, “Climate related sea-level variations over the past two millennia,” explains

The rate of sea level rise along the U.S. Atlantic coast is greater now than at any time in the past 2,000 years — and has shown a consistent link between changes in global mean surface temperature and sea level….

“Sea-level rise is a potentially disastrous outcome of climate change,” says [co-author Benjamin] Horton, “as rising temperatures melt land-based ice, and warm ocean waters.”

The NSF-funded work is “the first continuous sea-level reconstruction for the past 2,000 years.” The Proceedings of the National Academy of Sciences study concludes, “Using an extended semiempirical modeling approach, we show that these sea-level changes are consistent with global temperature for at least the past millennium.”


The figure above is from a 2009 PNAS paper, “Global sea level linked to global temperature” by two of the authors of the new paper, Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research and Martin Vermeer of Helsinki University of Technology. The new study “reinforces those projections in my view,” according to Rahmstorf. “AR4” stands for the lowball projections of sea level rise (SLR) that were made in the IPCC Fourth Assessment report.

We are currently close to the A1FI emissions pathway, though frankly, none of the IPCC models encompass the most dangerous of the amplifying carbon-cycle feed backs (the melting permafrost, see here), not do most SLR models encompass the staggering polar warming we face on our current path (see M.I.T. doubles its 2095 warming projection to 10°F — with Arctic warming of 20°F)

Even so, the recent scientific literature makes clear we are likely to blow past the AR4 projections by mid-century (see “JPL bombshell: Polar ice sheet mass loss is speeding up, on pace for 1 foot sea level rise by 2050”).

Co-author Michael Mann, director of the Earth System Science Center at Penn State, explained the significance of the new research in an e-mail:

The internal consistency that the study provides between estimated changes in sea level rise over the past millennium, and previously documented changes in temperatures, reinforces the fact that the recent warming is not only anomalous — it has obvious consequences, in this case, for rising sea levels. The longer timeframe provided by this study also provides for increased constraint on the parameters used in semi-empirical models of sea level rise. That increased constraint points toward projected sea level rise lying at or near the upper range of current projections, more than a meter by the end of this century under business-as-usual carbon emissions.

The temperature reconstructions of the past one thousand years have, contrary to the anti-science disinformers, been reproduced by multiple, independent studies. The evidence has become overwhelming that recent global warming is unprecedented in magnitude and speed and cause (see “Two more independent studies back the Hockey Stick and links therein).

As the new study concludes:

We have presented a unique, high-resolution sea-level reconstruction developed using salt-marsh sediments for the last 2100 y from the US Atlantic coast. Post-AD 1000, these sea-level reconstructions are compatible with reconstructions of global temperature, assuming a linear relation between temperature and the rate of sea-level rise. This consistency mutually reinforces the credibility of the temperature and sea-level reconstructions.

Here is a simplified version of the key figure [click to enlarge]

The bottom line is that we have more confidence both in the temperature reconstructions of the past 1000 years and in the recent higher-end projections of sea level rise in the next hundred years: “Sea levels may rise 3 times faster than IPCC estimated, could hit 6 feet by 2100.”


Did I mention the time to act was over a decade ago, but acting now is considerably better than continuing to listen to the disinformers’ plea to keep doing nothing?

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