High Water: Greenland ice sheet melting faster than expected and could raise East Coast sea levels an extra 20 inches by 2100 — to more than 6 feet

“The indispensable blog” — Tom Friedman, New York Times

The eastern United States must plan on the very real possibility that total sea level rise by 2100 will exceed 6 feet on our current emissions path. Sadly, the Washington Post got the only story half right.

This week I’ll focus on our best understanding of the impacts that Americans face from human-caused climate change.  On Tuesday, the US Global Change Research Program is releasing its long-awaited comprehensive analysis of Global Climate Change Impacts in United States.  We’ll see how it matches up against my not-so-well-funded analysis, “Yes, the science says on our current emissions path we are projected to warm most of U.S. 10 – 15°F by 2100, with sea level rise of 5 feet or more, and the SW will be a permanent Dust Bowl.”

First, though, let’s do a comprehensive review of projected sea level rise (SLR), starting with two recent studies on what accelerated melting of the Greenland ice sheet might mean for us.  The University of Alaska Fairbanks reports on a brand new study in the journal Hydrological Processes (subs. req’d):

The Greenland ice sheet is melting faster than expected according to a new study….

Study results indicate that the ice sheet may be responsible for nearly 25 percent of global sea rise in the past 13 years. The study also shows that seas now are rising by more than 3 millimeters a year–more than 50 percent faster than the average for the 20th century.

UAF researcher Sebastian H. Mernild and colleagues from the United States, United Kingdom and Denmark discovered that from 1995 to 2007, overall precipitation on the ice sheet decreased while surface ablation–the combination of evaporation, melting and calving of the ice sheet–increased. According to Mernild’s new data, since 1995 the ice sheet lost an average of 265 cubic kilometers per year, which has contributed to about 0.7 millimeters per year in global sea level rise.

This research is consistent with data presented at the annual meeting of the American Geophysical Union in December (see “Two trillion tons of land ice lost since 2003, rate of Greenland summer ice loss triples 2007 record“).  This staggering ice loss is all the more worrisome because it was not predicted by the IPCC’s climate models. As Penn State climatologist Richard Alley said in March 2006, the ice sheets appear to be shrinking “100 years ahead of schedule.” In 2001, the IPCC thought that neither Greenland nor Antarctica would lose significant mass by 2100. They both already are.

And, of course, Greenland is facing an almost incomprehensible amount of warming if we stay anywhere near our current emissions path — see “M.I.T. doubles its 2095 warming projection to 10°F — with 866 ppm and Arctic warming of 20°F.”

Especially worrisome for North America is that a new study in Geophysical Research Letters (subs. req’d) finds that sustained high rates of Greenland ice loss could lead to staggering increases in coastal sea level rise.  As reported:

If Greenland’s ice melts at moderate to high rates, ocean circulation by 2100 may shift and cause sea levels off the northeast coast of North America to rise by about 12 to 20 inches (about 30 to 50 centimeters) more than in other coastal areas. The research builds on recent reports that have found that sea level rise associated with global warming could adversely affect North America, and its findings suggest that the situation is more threatening than previously believed.

“If the Greenland melt continues to accelerate, we could see significant impacts this century on the northeast U.S. coast from the resulting sea level rise,” says NCAR scientist Aixue Hu, the lead author. “Major northeastern cities are directly in the path of the greatest rise.”

All that is needed for the 20 inches of extra sea level rise is if Greenland’s melt rate continues at its current rate through 2050.

And the key point of this study is that this 20 inches would be on top of what ever sea level rise is caused by the ice loss in Greenland, Antarctica, and the inland glaciers, plus thermal explanation of the ocean.

How much sea level rise is that?  Well, if you read last week’s WashPost story on the second study, “East Coast May Feel Rise in Sea Levels the Most,” you’d get the bizarrely old SLR estimate from the 2007 IPCC report:

While the rest of the world might see seven to 23 inches of sea-level rise by 2100, the studies show this region might get that and more — 17 to 25 inches more — for a total increase that would submerge a beach chair.

[Note to WP:  Sea level rise is one of the most potentially devastating impacts of global warming to human civilization — so you need a more serious visual metaphor for it than submerging a “beach chair.]

The 7- to 23-inch estimate was out of date the minute it was published in 2007, since the IPCC froze virtually all new science inputs to its Fourth Assessment in 2005.  Why would the WP write an article about the very latest study of possible extra SLR in 2100 and then add it to a very old SLR estimate that was based on an even older literature survey?

Last year, the Bush administration itself explained in great detail that the IPCC’s projection, low-balled the sea level rise number — see US Geological Survey stunner: Sea-level rise in 2100 will likely “substantially exceed” IPCC projections.  Since big media still gets this wrong, let’s take a quick look at that study, which concluded “based on an assessment of the published scientific literature”:

Recent rapid changes at the edges of the Greenland and West Antarctic ice sheets show acceleration of flow and thinning, with the velocity of some glaciers increasing more than twofold. Glacier accelerations causing this imbalance have been related to enhanced surface meltwater production penetrating to the bed to lubricate glacier motion, and to ice-shelf removal, ice-front retreat, and glacier ungrounding that reduce resistance to flow. The present generation of models does not capture these processes. It is unclear whether this imbalance is a short-term natural adjustment or a response to recent climate change, but processes causing accelerations are enabled by warming, so these adjustments will very likely become more frequent in a warmer climate. The regions likely to experience future rapid changes in ice volume are those where ice is grounded well below sea level such as the West Antarctic Ice Sheet or large glaciers in Greenland like the Jakobshavn Isbrae that flow into the sea through a deep channel reaching far inland. Inclusion of these processes in models will likely lead to sea-level projections for the end of the 21st century that substantially exceed the projections presented in the IPCC AR4 report (0.28 ± 0.10 m to 0.42 ± 0.16 m rise).

What does the recent published scientific literature now project?

• Science 2008:  “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.”  The IPCC famously ignored increased ice dynamics in its projection.
• Nature Geoscience 2007 looked at the last interglacial period (the Eemian, about 120,000 years ago) — the last time the planet was as warm as it soon will be again.  Seas rose 1.6 meters (5 feet) per century “when the global mean temperature was 2 ^°C higher than today,” a rather mild version of where we are headed in the second half of this century.
• Science 2007 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.
• Nature 2009 used coral fossil records from the last interglacial warm period 121,000 years ago (when sea levels ultimately reached 15 to 20 feet higher than now).  It concluded “catastrophic increase of more than 5 centimetres per year over a 50-year stretch is possible.”  The lead author warned, “This could happen again.”

And here’s an extra update.  The 2008 Science paper, “Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise” with its 0.8 and 2.0 m projection for 2100, is widely considered to be the most credible, comprehensive, and authoritative recent estimate.  And yet consider just one piece of that analysis — the lower bound projection of the SLR contribution in 2100 from the ice caps and inland glaciers (other than Greenland and Antarctica), which the paper says is 0.17 meters (170 millimeters).

These inland glaciers are melting  unexpectedly fast (see ” Another climate impact comes faster than predicted: Himalayan glaciers “decapitated” and “Another one bites the dust, literally: Bolivia’s 18,000 year-old Chacaltaya glacier is gone.”

A 2009 Geophysical Research Letters paper, “Sea-level rise from glaciers and ice caps: A lower bound,” (subs. req’d) concluded a detailed analysis of actual glacier data:

If the climate continues to warm along current trends, a minimum of 373 ± 21 mm of sea-level rise over the next 100 years is expected from glaciers and ice caps. When compared to recent estimates from all other sources, melt water from glaciers must be considered as a particularly important fraction of the total sea-level rise expected this century.

So you can add a minimum of 0.2 meters to the lower bound of the Science paper — taking that paper’s lower bound to 1 meter.  Given how fast the Arctic is projected to warm on the BAU path, I wouldn’t be surprised if projections of the likely ice loss from Greenland will rise in the coming years.  Same for Antarctica (see “Q: How much can West Antarctica plausibly contribute to sea level rise by 2100?“).

Bottom line:  The entire U.S. should be planning on SLR of 5 feet by 2100 on our current emissions path.  And the eastern United States should plan on the very real possibility that total sea level rise will exceed 6 feet.