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Sea Level Rise: It Could Be Worse than We Think

A new analysis released Thursday in the journal Science implies that the seas could rise dramatically higher over the next few centuries than scientists previously thought — somewhere between 18-to-29 feet above current levels, rather than the 13-to-20 feet they were talking about just a few years ago.

The increase in sea level would largely come from the partial melting of giant ice caps in Greenland and Antarctica, which have remained largely intact since the end of the last ice age, nearly 20,000 years ago. But rising global temperatures, thanks to human greenhouse-gas emissions, have already begun to melt that ancient ice, sending sea level up 8 inches since 1880 alone, with as much as 6 feet or so of additional increase projected by 2100.

That’s not enough to inundate major population centers by itself, but coupled with storm surges, it could threaten millions of Americans long before the century ends. Around the world, sea level rise will put trillions in property at risk within the next few decades.

West Antarctic Ice Sheet.

Twenty-nine feet of sea-level rise, by contrast, or even 18, would put hundreds coastal cities around the globe entirely under water, displacing many hundreds of millions of people and destroying untold trillions in property. It would, in short, be a disaster of unimaginable proportions.

The only good news, said the study’s lead author, Andrea Dutton, a geochemist at the University of Florida, in an interview: “This isn’t going to happen overnight.” It takes a long time to melt such huge volumes of ice. But since global temperatures are likely to remain high for centuries once they’ve been ratcheted up, it might be inevitable.

This scary new scenario for Earth’s future comes from deep in the planet’s past. Geologists have long known that about 120,000 years ago, the world emerged from an ice age into a relatively warm interglacial period. Before plunging back into the deep freeze, global temperatures rose to about the level where they are now, or maybe a little warmer, and hovered there for perhaps 20,000 years.

Naturally enough, Earth’s glaciers and ice caps melted back significantly, and the ocean rose — and since this so-called Last InterGlacial (LIG) is the best example we have of what happens in a warmer world, scientist look to that time for an idea of where the planet is heading.

Getting a handle on exactly how high the ocean rose back then is complicated, however. Dutton and her co-author Kurt Lambeck, of the Australian National University, went about it by looking for fossilized corals, especially those of species that thrive right at the surface of the sea. Their very existence, therefore, shows just how high the ocean was when the corals were alive.

It’s also straightforward enough to calculate when a particular coral sample was alive, thanks to the same general sort of radioactive dating that gives the ages of ancient humans, for example.

There’s one big complication, though: local changes in sea level can vary a lot from the global average for all sorts of reasons.  In the past, scientists have generally left out many of these confounding factors to simplify their calculations. Dutton and Lambeck, by contrast, took them into account.

By itself, the new study would be important enough. But combined with a 2009 paper in Nature, it verges on being downright definitive. The reason: both analyses come to pretty much the same conclusion, using different evidence and different statistical tools. “The fact that both techniques come up with such similar answers,” said Ben Strauss, director of Climate Central’s Program on Sea Level Rise, “is a strong indication that they’re both on the right track.”

What all of this means for future sea level rise isn’t entirely certain. The world was a different place during the LIG, most notably because the Earth’s orbit around the sun was more elongated at the time.

“The Northern Hemisphere,” said Rutgers scientist Robert Kopp, who co-authored the earlier study, “got more intense sun in the summer, while the Southern Hemisphere had a longer melt season.” Overall, however, global temperatures were less than 4°F higher than they are today. If we keep adding heat-trapping greenhouse gases to the atmosphere at the current rate, said Kopp, “we could overshoot that within the next few decades.”

The key question then becomes how long temperatures will remain high, and how the world’s ice sheets will respond — especially the ice in West Antarctica, which could add 20 feet to the world’s oceans all by itself if it melted. Several recent studies suggest that could already be starting to happen.

Even without these new and ominous results, it was already clear that even a moderate amount of sea level rise poses a big danger to people living near the world’s coastlines (Americans can calculate their own risk for the near future by using Climate Central’s “Surging Seas” interactive map).

If the latest research continues to hold up, however, the future may be even riskier than we thought.


By Marco64 (43081)
on July 14th, 2012

I love how these climate articles begin: “....seas could rise dramatically higher…”  Yes, and they “could” dry up altogether. The earth “could” burst into flames tomorrow. Anything “could” happen, couldn’t it?  But the question is, will it?  If we look at the climate record we can say with great confidence that it most probably won’t. This is one of the great flaws of the AGW movement—much of what they’re concerned about is based on conjecture. In reality, global temperatures are on a downward trend (according to satellite data). The Antarctic ice cap is at above-normal levels. The Arctic ice cap is still below normal, but at levels that continue to increase from the 2007 low. There is plenty of evidence that supports natural climate cycles rather than uncontrollable heating. I think Lemonick knows this, and I think he’s scratching for every possible shred of evidence to support the continuing erosion of the AGW theory.

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By Hominid (Charleston/SC/29428)
on July 14th, 2012

‘rising global temperatures, thanks to human greenhouse-gas emissions’ - What nonsense!

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By Mr. R. L. Hails Sr. P. E. (No/Info/12345)
on July 14th, 2012

When scientists stop using terms such as, “imply, could, might, and maybe”; when they can predict the time at which phenomena WILL happen, within a decade, with certainty, then they deserve the respect due to knowledgeable people.  I note that 300 years ago, New York did not exist.  It may not exist 300 years from now.  “..... the future may be even riskier than we thought.”  I do not know of anyone who loses sleep over this, except a few odd folks.  Some predict the seas will rise in 3,000 years due to man’s carbon combustion.  But no one knows what energy source man will use at that time.  If the sea,”...could threaten millions of Americans long before the century ends.”, I suggest they slowly move to dry ground.  There are millions more concerned today with losing their employment due to whacky green house regulations.  My greater worry is that my hair is turning gray.

There is a distinct difference between scientific articles and bogey man stories, or comic books.

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By Chad Brick (Rose City, Michigan 48654)
on July 14th, 2012

The devastation of major cities around the globe due to unstoppable sea level rises of several meters?  Baah, that’s in the FUTURE.

What about US, NOW? I need my SUV to get to WalMart!  Don’t you know that I have a life to live?  Sheesh.

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By johnwerneken (vancpouver wa 98661)
on July 14th, 2012

BUT stopping man-caused warming would cost dozens of trillions, perhaps ten times a dozen trillion. It’s not worth trying to solve this problem. Many of the proximate factors causing the warming are however undesirable for other reasons - sprawl, waste, pollution in general, gross subsidies to the middle class and the car, geographic separation of work rest play etc. Also some alternatives will become steadily more practical: fission, fusion, and both Earth and Space-based solar.

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By Tom Macey (warrenton/va/20187)
on July 14th, 2012

This article is pure cr@p!

The author clearly states “Geologists have long known that about 120,000 years ago, the world emerged from an ice age into a relatively warm interglacial period. Before plunging back into the deep freeze, global temperatures rose to about the level where they are now, or maybe a little warmer, and hovered there for perhaps 20,000 years.” without even giving a hint of why the planet warmed up after claiming “But rising global temperatures, thanks to human greenhouse-gas emissions, have already begun to melt that ancient ice”

What caused the planet to cool and then warm. Why are we to believe that any warming that may be occuring is caused by humans and not the same natural forces that caused the planet to warm before??
Poor writng and junk science, If I were a teacher this articlw would rate an F-

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By Tom Moriarty (Arvada/Colorado/80005)
on July 14th, 2012

Mr. Lemonick says…

“rising global temperatures, thanks to human greenhouse-gas emissions, have already begun to melt that ancient ice, sending sea level up 8 inches since 1880 alone, with as much as 6 feet or so of additional increase projected by 2100.”

It has been 13 decades since 1880 and the global sea level has risen 8 inches.  It is 9 decades unti 2100, and he says there will be up to 6 feet more (72 inches) by then.  By my calculations, the average sea level rise rate between now and 2100 would have to be 13 times greater than the average sea level rise rate was between 1880 and now.

Here is a little help with the math…

8 inches / 130 years = 0.062 inches/year

72 inches / 90 years = 0.800 inches/year

( 0.800 inches/year)/( 0.062 inches/year)

Such a substantial acceleration of the sea level rise rate should be obvious in the sea level data, right?  Well, take a look for yourself.  The following link has a video that shows the sea level data from hundreds of tide gauge sites from around the world as archived by the Permanent Service for Mean Sea level (PSMSL).  Use your own eyes to look for the acceleration.

Or, you can look at all the data from all the individual tide gauge sites at a more leisurely pace at the PSMSL web page…

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By Dave Thomas (West Hills)
on July 14th, 2012

I’m not interested at all in anyone’s predictions who can’t show me how much the sea has risen in the last quarter century and propose a theory that is falsifiable to account for that amount of rise.

I don’t see that anywhere in this article. How can the author hope to be taken seriously without such evidence?

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By aed939
on July 14th, 2012

No city is going underwater.  They will build dikes if/when necessary, like in New Orleans and Amsterdam.  Just because it is below sea level does not mean that it will be underwater.

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By Tom Frankenbach
on July 15th, 2012

New evidence out that man caused the LIA. I would rather have warming than cooling. There is speculation that we will delay prevent another LIA with warming so this is a plus since another LIA would kill off massive amounts of population. There are far more positives with warming and we can cope much more easily with warming than cold from a LIA. Imagine if temperatures plunged and destroyed our food crops? We are making enormous progress on heat resistend food crops but I doubt there is anything we could due to adapt food crops to frigid weather.  We can easily deal with sea level rise. There are already numerous examples of man apapting to sea level rise. Not a problem.

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By John Englander (Boca Raton, FL 33486)
on July 15th, 2012

To Johnwerneken’s point: stopping or dramatically reducing emissions likely can and will happen by mid century. That seems to be within our technical capacity. It will probably save money as well.  As the above story suggests however, the problem is the lag time for sea level adjustment. It takes centuries and is now well underway. It can no longer be stopped. But what we do can slow—or accelerate—the process of melting the ice sheets.

As for Tom Macey’s doubts or questions about the article. It did not mention it, but the natural cycle of the ice ages, every 100,000 years, for the last few million is rather well understood. It is known as the Milankovitch cycle, and is about a one percent change in the heat received globally from the sun, which changes in known cycles due to variations in solar orbits, etc.

What has generally not been explained is that sea level changes hundreds of feet naturally. Just 20,000 years ago it was almost 400 feet lower. Now it is rising, well beyond the natural cycle. This follows the correlation of Sea level, temperature, and CO2.  For graphs and a more complete explanation see

Fyi, I have spent the last three years studying all the information about sea level for a book to be released in the next month or two: “High Tide on Main Street: Rising Sea Level and the Coming Coastal Crisis.”

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By David F. (Ohio)
on July 15th, 2012

“Why are we to believe that any warming that may be occuring (sic) is caused by humans and not the same natural forces that caused the planet to warm before?? (sic)”

Maybe this [], coupled with carbon dioxide’s known behavior of absorbing radiation within the thermal infrared range? It’s a good thing Mr. Macey isn’t a teacher. He fails both physical chemistry and grammar.

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By Eric W (Norcross)
on July 15th, 2012

Even if the chicken little forcast that this guy has comes true. That a 4 degree increase in the temperature happens. Hell, lets give him 6 degrees. In Antarctica the high temperature only gets above minus 6 degrees for about 4 weeks. So for 11 out of twelve months all the water will freeze. On average that is 200 inches or 16 feet a year. It only takes about an IQ over 10 and 15 minutes to debunk these people. Google “Vostok Ice Core”. Oh, just one question. Why is there a place called Western Antarctica?

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By kester strange (deville, LA,71328)
on July 16th, 2012

I suspect that the writer is also one of the people who helped choose Al Gore as a spokesman for the movement. Such a choice speaks loudly about the thinking process of these so called weather experts.

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on July 21st, 2012

Another chorus of deniers saying “AGW isn’t real!”, but would REALLY like to see them quote a peer reviewed study that CAN explain the phenomena we’re seeing some other way.

Every theory has imperfections, but the most credible theory, supported by the most scientific observations is that Global Warming is caused by Human Activity. If there is an explanation that makes more sense. Please point it out.

Also, let’s all remember that the deniers first said, “Global Warming isn’t happening.” When that position became untenable, to all but the most intractable imbeciles they started saying “It’s happening, but we don’t cause it.” That position is becoming more ridiculous (see paragraph one) so now, we hear “It’s happening, but it’s not going to be as bad as they say!” (even though nature continuously beats the scientific predictions) or better yet - “We’ll adapt to it.” 

This last one is rich - seeing as how deniers biggest concern is always, how “expensive” it will be to a avoid the worst consequences of Global Warming. Imagine the costs of building dykes around every coastal city in the world, the cost of failed crops and new disease vectors, the continued rise in natural disaster frequency and intensity (I can assure the insurance industry knows this is real), and increased wars due to all these factors destabilizing countries and creating “climate refugees.”  You think mitigation is expensive - you ain’t seen nothin yet.

Someone wise once said,  “An ounce of prevention is worth a pound of cure.” It’ll never be more true than when talking about keeping the only place we have to live - habitable.

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By R S (Franktown/Colorado/80116)
on September 1st, 2012

Theory my butt, JP. LOOK AT THE DATA.  Sea level has been rising 8 inches per century for the last 80 centuries. If anything, it’s slowing down now.
There’s been no atmospheric warming in the last 12 years. Phil Jones, head of the Climate Research Unit at East Anglia, admits it. Data from RSS and UAH show it as well.
Since you feel free to call us imbeciles and “deniers”, here’s back at you. YOU are the imbecile. Science is based on observable facts, not a theory manufactured by graduate students and their professors, looking for money they don’t deserve for such foolishness.
JP wants a theory? Consider variations in solar radiance and magnetic field strength; both are much more important that a trivial change in a trace gas that absorbs in a small portion of the Earth’s emission spectrum.

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