Sea Level Rise: It Could Be Worse Than We Think

by Michael D. Lemonick, via Climate Central

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.

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.

Michael D. Lemonick covered science and the environment for TIME magazine for nearly 21 years, where he wrote more than 50 cover stories, and has also written for Discover, Scientific American, Wired, New Scientist and The Washington Post. This piece was originally published at Climate Central and is reprinted with permission.

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30 Responses to Sea Level Rise: It Could Be Worse Than We Think

  1. Paul Klinkman says:

    Now they tell us.

    Numbers of us in the online community have been saying for years that sea level rise numbers were probably too conservative.

    The real killer is enhanced storm surges. It’s not like the sea is mildly going to creep up. No, it’s going to wash out neighborhoods all at once, and sooner than the residents think. A category 2 Hurricane Katrina produced a 38 foot storm surge.

  2. I understand that studies into the impact of London flooding (following a storm surge co-incident with highest tides) suggest that once flooded the city would effectively need to be abandoned. Fresh Water supplies would be early casualties together with sewerage, utilities, transport, telecoms (all of which rely on the network of tunnels beneath the city. The London underground would not reopen.

    If this is the case in a “first world” city we can be sure that the horrors of climate-change are yet to be appreciated.

    By the time we act it may be too late, to prevent catastrophy, but inaction is not excusable even if it is too late, because we should at least attempt mitigation.

  3. Bob Savage says:

    Great points @Paul.

    Regarding storm surges: and the 2011 Tsunami waves were 133 feet high and washed as far as 6 miles inland. The problem isn’t just sea level rise, it is what happens when extreme events occur. Simple answer = even worse things happen. The environmental refugees of the future will look back at this age in disgust.

  4. Another very big problem is

    Groundwater intrusion
    Beach erosion

    And all the flooded soils will start decomposing faster, hence another powerful feedback loop from more methanogenesis.

  5. Should read = Saltwater intrusion

  6. “In other words, the Nature study says that during the last interglacial (the Eemian) evidence now suggests sea levels rose 20 inches per decade for five straight decades — a roughly 8-foot rise in a half century.

  7. Dick Smith says:

    RE: “…over the next few centuries than scientists previously thought — somewhere between 18-to-29 feet above current levels…”

    Am I the only one who finds this kind of reporting absolutely maddening? HOW MANY CENTURIES?

    If anyone has that information, I’d sure appreciate it. A graph with a range would be

  8. Joe Romm says:

    We don’t know. Up to 6 feet or so this century. More next century.

  9. Lou Grinzo says:

    The ultimate example of endangered people living near coastlines has to be Bangladesh. As Heidi Cullen points out in her book, that country has half the population of the US squeezed into an area the size of Iowa, with a large portion of it barely above sea level. This one country alone could well produce millions, even tens of millions, of climate refugees this century.

  10. When it comes to money, Florida will be the state with the largest impact for the US. Which means one of the largest US economies will go down, probably we can see this in our life time, with more destructive storm surges and locals will getting even more problems from salt water intrusion.

  11. To understand that we face not a gradual deterioration of the situation, rather then rapid developments with wide impacts. One has just to look at the New Orleans area in the aftermath of Kathrina and the following mortality rates of what was/is left of the local population.

  12. The main psychological obstacle we face with climate change, might be the lack of hope. We are sealing our faith today and wait for a self fulfilling prophecy – for the Genesis flood myth of our times.

    What do you do when you know that large parts of the world become uninhabitable? There is so much chaos about to erupt, that it will be soon impossible to act on climate change.

    The chaos will only cause more usage of fossil resources, because we lose the driver for technological advancement (deployment of alternatives) when civilization, markets, food supplies, psychs, all kind of systems collapse.

  13. The amplifying feedback mechanism of polar ice melt is the so-called albedo-flip effect, where loss of reflection by melted ice is compounded by infrared absorption by open water, a process currently taking place in the Arctic Sea, as reported by Hansen et al. [1], [2]: “… amplifying feedbacks make ice sheet disintegration necessarily highly non-linear. In a non-linear problem, the most relevant number for projecting sea level rise is the doubling time for the rate of mass loss. Hansen (2007) suggested that a 10-year doubling time was plausible, pointing out that such a doubling time from a base of 1 mm per year ice sheet contribution to sea level in the decade 2005-2015 would lead to a cumulative 5 m sea level rise by 2095.”

  14. “Just the melting of all the floating ice in the arctic ocean, will add as much heat to the earth, as all the Co-2 we put in the atmosphere to date.” Dr. James Lovelock

    Estimating the Global Radiative Impact of the Sea-Ice-Albedo Feedback in the Arctic
    a more realistic ice-free-summer scenario (no ice for one month, decreased ice at all other times of the year) results in
    a forcing of about 0.3 W m−2, similar to present-day anthropogenic forcing caused by halocarbons. The potential for changes in cloud cover as a result of the changes in sea ice makes the evaluation of the actual forcing that may be realized quite uncertain, since such changes could overwhelm the forcing caused by the sea-ice loss itself, if the cloudi- ness increases in the summertime.

  15. Rabid Doomsayer says:

    When I checked the temp for Alert, the last available figure was 17 C. Is that even possible?

    2007 showed us that a huge ice loss can result from ice export. 2012 is showing us it can melt in situ. If Maslowski is right, then we will see zero minimum sea ice in the next few years. Then no summer sea ice not long after that.

    Then you can expect an acceleration of the GIS melt.

    Have you stopped to think just how very gentle the Milankovitch cycles are? What we have done is not at all gentle in comparison and yet we are expecting slower changes.

    Probably safe to assume there will be more bad news on the sea level projection front.

  16. If the number reaches 560 ppm, a doubling of preindustrial values, sea level globally could rise 25 meters, according to Eelco Rohling, professor of ocean and climate change at University of Southampton in the U.K., who presented data at the AGU meeting with Hansen. Many large cities worldwide lie at that elevation or lower. The two scientists agreed that if nations continue to emit CO2 at current rates, the world could reach 560 ppm by 2100.

    The paleoclimate record also shows that 560 ppm would be enough to melt all the ice in the Arctic, and later the Antarctic. Rohling said that once the Antarctic melts, sea levels would rise by 60 to 70 meters. “If governments keep going the way they are going,” Hansen added, “the planet will reach an ice-free state.”

  17. Merrelyn Emery says:

    While not having anywhere near the population of Bangladesh, the small Pacific Island nations such as Kiribas, Tuvalu etc are under immediate threat now with destroyed land, lack of fresh water etc. They already have plans for staged evacuation to NZ etc, ME

  18. Climate-affected Bangladesh people pushed to acute poverty

    “We lost our home due to erosion of the Meghna two years ago and were compelled to move to Chittagong city looking for shelter.”

    As Bangladesh is facing the adverse impacts of extreme climate events, including cyclone, tidal surge, erosion, flood and erratic rainfall, migration rate from rural to urban areas has been increasing day by day. Most of the people are migrating from islands and char areas to other places in the country, particularly in cities and towns.

    About the recent trend of migration of displaced people, Sunil Chandra Das, who took shelter on the Patenga-Halishahar embankment nearly 30 years back after losing his house due to a tidal surge, said that when he migrated to Chittagong city from an island of the Bay of Bengal, only few families used to live on the coastal embankment. “But, now thousands of internally migrated people are living on the embankment after losing their homesteads due to natural disasters,” he said.

    According to the Intergovernmental Panel on Climate Change (IPCC), if the sea level will rise one meter due to global warming by 2050, the country’s one-third of land will go under the sea water.


    Updated my blog post on the topic a bit. Still room for improvements. So i learned today from a recent RC article that the Antarctic is warming too – contrary to conventional wisdom (which predicted cooling).

  20. Aussie John says:

    Sea level rise will continue as long as industry continues with “business as usual”.

    Big business has demonstrated it will operate regardless of any form of government for its own self interest – the common good of world citizens emerges only as a secondary benefit.
    At this time in our history ( thanks to unsustainably cheap energy and technological advances etc) capitalism is able to operate completely unfettered of historical limitations, except of course for Earth’s diminishing sustainability boundaries.

    The inevitable natural consequences of ignoring these boundaries are delayed by several/many years – this unfortunate delay is used by opportunistic corporations to amass vast profits; while buying necessary political influence and orchestrating extensive media propaganda campaigns to convince a gullible and selfish public that all is well with “business as usual”.
    A number of very talented and influential media personalities are sponsored; their egos stoked by abundant financial rewards and career success; their use is not unlike mercenary “Judas” goats; to misrepresent scientific advice and reinforce “useful” prejudices of an uninformed complacent public.
    The Earths environmental survival boundaries however are real and inflexible; they cannot be extended no matter how powerful the entity.
    The problem the Earth is facing is indeed diabolical;
    extreme capitalism practiced by ever bigger ruthless inhuman corporations; with no conscience or moral responsibility; selfishly encouraging and exploiting a common human failing – insatiable greed.
    In the event this evolution of “big business” is allowed to proceed to conclusion, it will inevitably create a capitalist dictatorship of world economic order.
    Very few, wealthy entities may retain control for perhaps few hundred years at most; while an unfortunate side effect will be that the vast bulk of humankind/animal-kind will perish as living conditions deteriorate in the polluted climate.
    The essential unwelcome, unpalatable, and painful issue we must confront is this:-
    our current system of capitalism cannot function in an environment limited by sustainability boundaries – when unregulated growth is no longer possible.
    The model that has worked for hundreds of years has reached Earths practical limit.

    Capitalisms innate driver, of most handsomely rewarding the most efficient practitioners of “profit now, pay later”, combined with the curse of corporate greed have led us to the current crisis of sustainability. Its failure to acknowledge the requirement to provide meaningfully for the future is the cause of its downfall.
    Unfortunately big business will have to be dragged kicking and screaming towards implementation of sustainable operations, as it means an end to the irresponsible open ended boundless profit mentality.
    Perhaps it will take some disastrous and calamitous worldwide corporate failures to occur before the first corporate entity is convinced to cooperate to achieve sustainable operations.
    The reward of course, will be long term stability, albeit with lower profits and returns.
    To achieve the objective of restoring control we must urgently apply our intellect to the daunting challenge of development of an alternative sustainable system of corporate / business governance. Failure to find and adopt a suitable system is not an option, as the catastrophic failure of the current system is as certain as the current un-sustainability of advanced industrialised economies.

    If the various national governments of earth cannot restore control of runaway “Big Business” behemoths, I fear that life as we know it on Earth is doomed to oblivion.
    If the successful development or design of such a system proves be a pipe-dream, we are in deep trouble.
    Nature has its own brutal way of controlling plagues – sea level rise is but one part of natures plague control plan.

  21. I find this fascinating, a certain species is growing to an extend where it’s technological actions shift the climate change, which in turn is changing the habitable environment and shrinks already sparse spaces for population growth.

    It appears almost as if earth is about to teach us the hard way, how we have to exist. Every species in the universe will reach these boundaries, when it gets big enough to change the atmospheric compositions. We are better of with the holocene climate, but now we create a less life favoring cosmos, with the result of civilization collapse and possible human extinction, because of less resources and human turmoils.

    Nature favors a species which can figure out how to live in balance with the environment. We are likely not one of these species. The truth hurts.

  22. Joan Savage says:

    It only takes a pressure shift in coastal groundwater flow to make a coast largely uninhabitable due to saltwater intrusion into coastal aquifers and streams.
    That happens long before surface inundation.

  23. Joan Savage says:

    That is to say, permanent surface inundation. Obviously we see coastal storms that slosh up onto land and drain away.

    A recent example of the pressure dynamics is the tongue of saltwater creeping upstream in the Mississippi. The river is slowed by drought conditions so it does not push saltwater back downstream.

  24. In our future of higher seas, at sometime people will look back to these decades of denial.

    Will it be with scorn or bemusement? Or just a shrug?

  25. Jim Baird says:

    Nature’s response to an overheating ocean, over 90% of the heat attributable to climate change has gone into the oceans, is to convert the excess heat to work in the form of a hurricane.

    We could and should be doing the same thing producing all of the energy we need with ocean thermal energy conversion.

    (Disclosure – patents pending)

  26. Anne says:

    Hello and thank you for this article. So-called environmentally induced migration is multi-level problem. According to Essam El-Hinnawi definition form 1985 environmental refugees as those people who have been forced to leave their traditional habitat, temporarily or permanently, because of a marked environmental disruption (natural or triggered by people) that jeopardised their existence and/or seriously affected the quality of their life. The fundamental distinction between `environmental migrants` and `environmental refugees` is a standpoint of contemporsry studies in EDPs.

    According to Bogumil Terminski it seems reasonable to distinguish the general category of environmental migrants from the more specific (subordinate to it) category of environmental refugees.

    Environmental migrants, therefore, are persons making a short-lived, cyclical, or longerterm change of residence, of a voluntary or forced character, due to specific environmental factors. Environmental refugees form a specific type of environmental migrant.

    Environmental refugees, therefore, are persons compelled to spontaneous, short-lived, cyclical, or longer-term changes of residence due to sudden or gradually worsening changes in environmental factors important to their living, which may be of either a short-term or an irreversible character.

    According to Norman Myers environmental refugees are “people who can no longer gain a secure livelihood in their homelands because of drought, soil erosion, desertification, deforestation and other environmental problems, together with associated problems of population pressures and profound poverty”.

  27. Mulga Mumblebrain says:

    I’ll bet that these grim prognostications will, in turn, be superseded by even more dire ones. Without exception the predictions of the climate establishment have turned out to be hopelessly underestimating the catastrophe. I’d really love to see just one example of ‘alarmist’ overstatement. Just one. Even the ‘by 2035 most glaciers in the Himalayas’ will be effected by climate change looks a pretty good bet to me. The silly story that it was meant to be 2350 is pure bulldust. At the current rate of deterioration by 2350 there won’t be any ice left on the planet and we’ll be long gone.

  28. Mulga Mumblebrain says:

    Quite correct. If by some miracle we could be led to address the catastrophe we would stand some chance of displaying resilience in the face of the coming disasters. But with our carefully nurtured and inculcated denialist, magical thinking, when the horrors arrive we will become a dangerous destructive mob, where it will be every man for himself and the Devil take the last. The ‘bellum omnium contra omnes’. A global Mogadishu or Beirut in the bad years. Fortunately for the Right this is their vision of the ideal society, and we already have a politer version in neo-liberal sado-monetarism, and the austerity that is tearing the heart out of societies from Ireland to Haiti and Latvia and Greece. If there is one thing the Right loves even more than ‘The Invisible Hand’ of the Market, it’s the all too ‘Visible Fist’ of ‘Might makes Right’.

  29. Mulga Mumblebrain says:

    Our terminal predicament derives directly from oligarchic rule by rich psychopaths, who gained their money from parasitism on the human host and the natural world, or by inheriting it from earlier generations of the same type. The popular phantasy that the elites are alien reptilians is a metaphor for the true, wretched reality-that the worst type of human, those most driven by insatiable greed, the most unscrupulous, amoral, violent and antipathetic to other human beings, has seized control of humanity from ‘the mammals’, ie the vast majority. Some mammals, being of low intellect and questionable psychology, have been brainwashed to accept the reptilian agenda, although they have no chance of ever being a ‘winner’ in this rigged contest. And the cold-blooded ones have created an operating system, capitalism, over the centuries, that solidifies and perpetuates their omnicidal dominance. Both must go if we are to have any hope of human society surviving, or deserving to survive.

  30. Solar Jim says:

    Behind our current figure of about 400 ppm, lies a higher figure nearer to 500 ppm for total carbon dioxide equivalent. A large factor tempering this eventual impact today are temporary aerosols. They are temporary to the extent that they fall out in days whereas carbon dioxide is rather permanent (conservation of matter).