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New Research Lowers Past Estimates of Sea-Level Rise

Posted on 19 March 2012 by John Hartz

This is a reprint of a press release issued by the National Science Foundation (NSF) on  March 14, 2012.


Projections for the future still loom large

Beach deposit in the Bahamas

New explanation for why beach deposits in the Bahamas are 70 feet above sea level.

Credit: Paul Hearty



The seas are creeping higher as the planet warms. But how high could they go?

Projections for the year 2100 range from inches to several feet, or even more.

The sub-tropical islands of Bermuda and the Bahamas are two seemingly unlikely places scientists have gone looking for answers.

The cliffs and ancient reefs on Bermuda and the Bahamas have lured fossil-hunters for decades. The land on the Bahamas, for example, has a foundation of fossil coral; the stone is derived from the disintegration of age-old coral reefs and seashells.

These areas are now attracting scientists investigating global sea level rise.

By pinpointing where the shorelines stood on cliffs and coral reefs in the Bahamas and Bermuda during an extremely warm period 400,000 years ago, researchers hope to narrow the range of global sea-level projections for the future.

After correcting for what they say was sinking of these islands at that time, scientists estimate that the seas rose 20 feet to 43 feet higher than today--up to a third less than previous estimates, though still a drastic change.

The study infers that the Greenland and West Antarctica ice sheets collapsed during the ancient warm period, but that ice loss from the vast East Antarctic Ice Sheet was negligible.

The results are reported in this week's issue of the journal Nature.

"Our research provides a simple explanation for high beach deposits [such as fossils in the Bahamas]," said the paper's lead author Maureen Raymo, a scientist at Columbia University's Lamont-Doherty Earth Observatory.

Average global sea-level rose eight inches since the 1880s, and is currently rising an inch per decade, driven by thermal expansion of seawater and melting of glaciers and ice sheets, including the still mostly intact ice in Greenland and West Antarctica.

In its most recent report, the Intergovernmental Panel on Climate Change estimated that the seas could rise up to two feet by 2100.

That number could go higher depending on the amount of ice melt and the quantity of greenhouse gas emissions.

The United Nations estimates a five feet sea-level rise would be enough to swamp 17 million people in low-lying Bangladesh alone.

The new study factors in the loading and unloading of ice from North America during the ice ages preceding the long-ago sea-level rise.

As the ice sheets grew, their weight pushed down the land beneath them while causing land at the edges--Bermuda and the Bahamas--to bulge upward, says Raymo.

When the ice pulled back, the continent rebounded, and the islands sank.

"We're re-thinking many of our estimates of past sea-level rise now that we're more aware of the effects of unloading of ice," said Bil Haq, program director in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research. "We now have a meaningful way of calculating the rebound.

"This study is a good example of collaboration between paleoceanography and geophysics to resolve an important issue: the question of future sea-level rise."

Today, both Greenland and West Antarctica are losing mass in a warming world, but signals from East Antarctica are less clear.

Raymo said the research helps show that "catastrophic collapse" of the East Antarctic ice is probably not a threat today.

"However, we do need to worry about Greenland and West Antarctica."

Source paper:

Maureen E. Raymo & Jerry X. Mitrovica, “Collapse of polar ice sheets during the stage 11 interglacial”, Nature(2012), doi:10.1038/nature10891

The Abstract of this article was posted online on Mar 14, 2012


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Comments 1 to 18:

  1. So there's another shoe to drop, when the 'rethinking' has been done? I'm a bit surprised that glacial rebound wasn't more thoroughly factored in in the first place. It's not all that obscure an effect!--or so I'd have thought.
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    Moderator Response: [JH]Science is a continuous process of discovery and learning.
  2. So the East Arctic ice sheet won't melt away in my lifetime. Phew! I'm feeling much better now.
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    Moderator Response: [JH] That would be the "East Antarctic" ice sheet.
  3. Sure ... except now during a long inter-glacial, the sea-shore is 70 feet above sea-level while an isostatic rebound theory suggests it should be closer to sea level. It should be 70' above plus the additional sea-level lowering when its end of the teeter-totter is looking at mile-high ice-sheets. They're addition of an additional 20-43' during an Ice Age doesn't address the current location. If they're suggesting the Hoxnian stretch of 50k years had the Bahamas slooowwwly sink to the sea, it should mesh with evidence from at least Nassau all the way to Turks&Caicos. For now, I'll stick with a local vertical push from below. But it's an interesting hypothesis ... better than "The Flood".
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  4. Another prediction... ...somewhere a Denialatus - or several - will conflate the Carribean correction as needing to be applied to contemporary rise that presently occurs, and to future sea level that will occur in future, as a consequence of thermal expansion and ice melt.
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  5. One useful rule of thumb relating to ice is: if all the glaciers melt sea levels will rise by 0.7 m, if Greenland melts by 7 m, if Antarctica melts by 70 m. Different sources give slighlty different figures but it's accurate enough to put things in perspective.
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  6. Doc Snow @ 1 My! I wish I had 20/20 hindsight. It would be really useful to appear clever by being able to state the flipping obvious. But there again, appearances can be deceptive.
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  7. I'll look forward to reading the paper, but frankly its nice to get some good news from the climate front for a change.
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  8. Suggested reading: “Sinking land shows East Antarctic ice sheet is stable”, by Sara Reardon, New Scientist, Mar 19, 2012 This article sheds more light on the significance of the findings discussed in the OP.
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  9. Please note that I have amended the OP by adding the name of the source paper and a link to its Abstract.
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  10. "was posted online on Mar 14, 2912" And I just read Kate's article which starts with "To the citizens of the world in the year 5000: It’s 2012, and nobody is thinking about you" You are a third of the way there.
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    Moderator Response: [JH] Unforced error corrected.
  11. Is not the plastic phase of isostatic rebound that happens first much quicker? There is already measurable rises in the edges of Greenland as the ice sheet edge thins. So We have to add this effect to the effective sea level rise.
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  12. To mitigate sea level rise (possibly completely) we just need to control the weather to dump moisture on the Antarctic ice sheets like nature does Control of weather, e.g. 5G_2002_Weather_Hoffman_February_2002 will happen well before catastrophic sea level rise takes place. This would not mitigate more acidic oceans, etc.
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  13. Eric, this would have to be the most extraordinary display of hope that I have every seen. None of the required technologies are even on the horizon so why do you believe that could happen before "catastrophic sea level" rise. (I'd define sealevel rise of 10mm/yr as catastrophic - what is your definition?). Furthermore, the idea that moving precipitation to Antarctica also means that you are moving heat to Antarctica as well. The isolation of Antarctica by circumpolar ocean and atmospheric currents is what is keeping it cold. You could get short term growth in central regions and even faster loss on the margins. The smart strategy is hope something good helps but act on the basis of what is likely. You cant be seriously proposing this as a reason for doing nothing?
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  14. scaddenp, your definition of catastrophic SLR seems reasonable. This idea is not a reason to "do nothing" but one reason among others not to worry about sea level. The paper shows positive ice mass without any intervention, not what you describe. I don't describe this as hope but the inevitable complete control of nature from macro to micro. The question you would normally ask me is who pays for these measures. Part of my answer is here but admittedly will work better for CCS than weather control.
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  15. Wild speculation about what might be possible in the future without a single line on the thermodynamics does not translate into "a reason not to worry about sealevel". You assumed "control" of micro processes would allow you violate that thermodynamics boundary conditions which I dont think the author implies at all. Inferring from that discussion that it was "inevitable" to gain weather control, is frankly amazing. The science paper discusses that increasing precipitation (from warming) was increasing snow cover, but as it turned out from the GRACE measurements, the paper was also wrong. There is already increased ice loss from edges, so you have net ice loss. If you want increased precipitation, then you have to move more warm moist air onto Antarctica from surrounding ocean. Where is most of that going to precipitate? Gains would be a passing phenomena only, especially if that precipitation starts falling as rain (making it a effective heat transfer mechanism) eg reported here. I didnt ask my usual question, as it is clear that a heatpump of the magnitude required (the only solution that make thermodynamic sense) would be fundable by the only by those responsible for the emissions.
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  16. Just for further clarity - my understanding of the speculative bit was that some large-scale processes (eg hurricane formation, monsoon path, maybe even ENSO timing) ultimately stem from small bification in chaotic system. However, much of climate is large-scale stable phenomena, bound by thermodynamic constraints. Eg changing timing of an ENSO event might be possible but not holding one back. The circumpolar system would another major stable system. The high pressure systems sitting on the poles are there because its cold, just as low pressure system dominate the tropics. No interference with dynamical systems can change this.
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  17. scaddenp, technological progress is always speculative but it is always inevitable. I'm not sure how you can make a thermodynamic argument because as you know, it is chaotic system control problem. The "stability" of the circumpolar circulation is more of a persistence than a stability. The presence of these lows: means that natural changes and/or GHG responses are starting to affect the weather and weather control can help that along. As this paper shows the Amundsen Sea low is currently the dominant feature for much Antarctic weather and moisture flux (as opposed to the Antarctic high). The rest of Antarctica will require transitory lows to penetrate the otherwise persistent (not stable) circumpolar flow.
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    Moderator Response: [DB] This line of discussion has digressed and is OT for this thread. Please find one of the solution threads if you wish to continue this. Thanks!
  18. I cant find a really suitable solution thread, but I have continued here.
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