New Research On The Rising Sea

Human caused greenhouse gas pollution has locked us into a situation where the global sea level will rise, at an unknown rate, high enough to inundate most major coastal cities and vast areas of agricultural land in low lying countries, and wipe out thousands of islands. Entire countries (small, low lying ones, and pacific ocean nations) will either disappear entirely or be made very small. Even as we head towards a likely limit in global food production in relation to increasing demand, large productive agricultural areas will be destroyed. As far as I can tell, there is nothing to stop this from happening, though reducing our greenhouse gas pollution to zero over the next several decades may prevent the global ocean from rising to its absolutely maximum amount.

So sea level rise is important.

The surface of the Earth comes in two forms: Ocean bottom and continent. They are totally different geologically, with the ocean bottom consisting of relatively heavy basaltic rock formed at the margins between spreading plates, and continents of lighter rock, generally formed from below.

The global ocean sits mainly on the oceanic plates, but at its edges (except in a very few special locations), it rests against those continents. Over time the sea rises and falls. When the sea is at its lowest point, with a good amount of its volume reduced because it is trapped in glacial ice, most of the continents are exposed. When the sea is at its highest point, vast areas of the continental margins are inundated. At present, the ocean is pretty high, covering much of the continental margin that it ever covers, but there is room to grow, with large areas of the coastline subject to future inundation.

Rising surface temperatures caused directly or indirectly by human release of greenhouse gas pollution melt glaciers and warm the ocean, both of which are causing the global sea level to rise. This is a long and complicated process. We add greenhouse gas, mainly CO2, to the atmosphere, and this causes warming, enhanced by various positive feedbacks that either cause an increase of additional greenhouse gases such as water vapor, methane, and more CO2, or reduce the ability of certain natural systems to absorb these gasses. The greenhouse gas causes warming, which causes more greenhouse gas, which causes more warming. Meanwhile, most of this extra heat is actually trapped in the ocean where it only contributes a little to melting glaciers, but does contribute to expanding the volume of the ocean. The ultimate amount of heating, and the ultimate amount of sea level rise, takes a long time to be realized, and the rate of this change is only roughly estimated.

What we have already done to the atmosphere will cause sea level rise to continue for a very long time, possibly many centuries, possibly thousands of years. We have increased the amount of CO2 in the atmosphere from the mid 200s parts per million (ppm) to 400ppm, and we expect that increase to continue for decades. Evidence from the past, through the science of paleoclimatology, tells us that when the atmosphere holds between 400ppm and 500ppm of CO2, the global sea level is many meters above the present level.

Understanding sea level change is therefore critically important to understanding the impacts of climate change. We can measure current sea level rise and assume that steady increase over time (even if it is a bit variable) is mostly caused by global warming, heating the ocean and melting glacial ice. But there are problems with these measurements and associated estimates. Recent research has shown that Antarctic, which holds most of the world’s ice, is or could or will contribute a very large amount of water to the sea. But, other recent studies show that some of the expected reduction in glacial size might not be happening at the rate previously estimated. At the moment, sea level is rising at a certain rate, and some research explains a good amount of that increase from melting ice, but other research takes that melting ice out of the equation and leaves that portion of the sea level rise unexplained, for now.

Past sea level change (up or down), prior to the industrial revolution when we started releasing all this greenhouse gas pollution, should give us a baseline against which to assess modern day measurements, and is an essential part of the process of understanding this critically important system. But it is difficult to measure sea level, at present or in the past. We can measure the current position of the sea at a given part of the continental margin by just going there and measuring it. Sea level over recent decades, going back in some places a few centuries, can be estimated using tide gage records. We can sink cores (or trenches) in relatively protected areas (such as behind barrier islands) and find organic material that would have been formed just below the surface of the sea, measure its elevation and date it, to give an estimate of sea level in the past. We can put the tide gage data and the coring data together and get a rough estimate of sea level change.

But that estimate is not just rough, but almost useless, without a lot of careful further study. As the organic material representing older sea levels is buried by later organic material or other sediment, it tends to be compressed and lower in elevation. The study of this process is many decades old, and this can be adjusted for, but it is complicated. The actual sea level at a given point along the coast depends partly on how big the ocean is at the moment (obviously) but also on the position and strength of major currents. At present, and many times in the past, the North Atlantic ocean is bunched up way out at sea because of the movement of currents. This lowers the sea level along the coast in many areas. But if these currents either move or change in their strength, this effect changes, and the coastal sea level goes up or down independently of the global sea level.

Wherever there were large glaciers, the land has been pushed down by the weight of the ice. After the glaciers melt away, the land rebounds. Where this happens along the coast, estimating global sea level from local sea level becomes quite complicated. Meanwhile at the outer edge of the glacial mass, the land is actually pushed up to compensate for the depression caused by the massive glaciers. This is called “forebuldge.” Forebuldge makes the sea level look lower than it should, until the forebuldge reduces and flattens out. Indeed, the rebound effects of enormous glaciers in Canada are still happening, changing the position of the shoreline of Hudson’s Bay fast enough that cabins built on the shore a century ago are now a long walk from the sea.

This is all manageable, and people have been working on collecting these data and figuring out how to use it since the 1960s. But now, this week, what may be the first research project to put most of these data together to provide a pretty good estimate of sea level variation over the last 3,000 years, has been published.

The key result from this paper is the graph at the top of this post.

Robert E. Koppa, Andrew C. Kemp, Klaus Bittermann, Benjamin P. Horton, Jeffrey P. Donnelly, W. Roland Gehrels, Carling C. Hay,b,k, Jerry X. Mitrovica, Eric D. Morrow, and Stefan Rahmstorf’s paper, “Temperature-driven global sea-level variability in the Common Era” (PNAS) does this:

We present the first, to our knowledge, estimate of global sea-level (GSL) change over the last ?3,000 years that is based upon statistical synthesis of a global database of regional sea-level reconstructions. GSL varied by ?±8 cm over the pre-Industrial Common Era, with a notable decline over 1000–1400 CE coinciding with ?0.2 °C of global cooling. The 20th century rise was extremely likely faster than during any of the 27 previous centuries. Semiempirical modeling indicates that, without global warming, GSL in the 20th century very likely would have risen by between ?3 cm and +7 cm, rather than the ?14 cm observed. Semiempirical 21st century projections largely reconcile differences between Intergovernmental Panel on Climate Change projections and semiempirical models.

So now we have a much better idea of the nature of global sea level rise for a couple thousand years prior to human greenhouse gas pollution, and we have a firm demonstration of the effects of this pollution on sea level over the last century or so.

We are fortunate that one of the authors of this paper, Stefan Rahmstorf, is a blogger at Real Climate, where he wrote this post summarizing the original paper (though the original paper, linked to above, is pretty readable!).

Climate Central produced this graphic based on the paper:


Of this, Rahmstorf says, “The fact that the rise in the 20th century is so large is a logical physical consequence of man-made global warming. This is melting continental ice and thus adds extra water to the oceans. In addition, as the sea water warms up it expands.”

How much will sea level rise by the end of the century?

In his post, Rahmstorf brings in a second study on sea level rise, also just published (see the RC post for more details). That research attempts to estimate the amount of sea level rise expectd by 2100. There are four separate studies, each using three different (RCP) assumptions about future human caused climate change, and each combination of study and model provides a range. In centimeters, the lowest numbers are around 25 (close to the amount that has already happened over the last century) and the highest numbers are around 130-150 (so, up to about five feet).

Rahmstorf appears to agree with my thinking on this, which is that these estimates don’t account for catastrophic deterioration of ice sheets and subsequent increase in melting, if such a thing results from what appears to be increasing instability of some of those glacial features. For example, huge parts of the Antarctic ice sheet are in the form of vast glacial rivers pinned in place by a precarious “grounding” of ice on rock near the mouth of those rivers.

If that grounding falls apart, the entire river can start to march to the sea very quickly, establishing a new grounding line upstream. It is possible that such a new grounding line is way upstream. As all that ice falls into the sea, it would likely expose high vertical cliff that would then start producing ice bergs at a very high rate for many years. There may be other features currently deep under the ice that would be exposed, such as pre-melted water near warm spots. In other words, the drainage of meltwater will not be made less efficient by such a collapse, but rather, more efficient, regionally and for a certain period of time. The point is, the impact on the rate of glacial melt of such events is pretty much unknown and very difficult to estimate.

Rahmstorf notes, “The projections on the basis of very different data and models thus yield very similar results, which speaks for their robustness. With one important caveat, however: the possibility of ice sheet instability, which for many years has been hanging like a shadow over all sea-level projections. While we have a pretty good handle on melting at the surface of the ice, the physics of the sliding of ice into the ocean is not fully understood and may still bring surprises. I consider it possible that in this way the two big ice sheets may contribute more sea-level rise by 2100 than suggested by the upper end of the ranges estimated by Mengel et al. for the solid ice discharge, which is 15 cm from Greenland and 19 cm from Antarctica. (The biggest contributions to their 131 cm upper end are 52 cm from Greenland surface melt and 45 cm from thermal expansion of ocean water.)”

He backs this up by reference to other recent studies showing that ice sheets have in the past broken up at surprisingly high rates.

One and a half meters, or five feet, of sea level rise within the lifetime of those born today is possible. Half of that is extremely likely. Double that may even be a possibility. This is expected to continue for centuries, even millennia, or until all the ice melts, whichever comes first.

How many things in your life originate from some thing that happened in the past? The invention of agriculture (that happened many times from about 10,000 to 4,000 years ago), the invention of writing (again, multiple times, thousands of years ago), the modern western system of government and law (depending on where you live, the Magna Carta, the US Constitution) hundreds of years ago. If you are religious, it is likely that your religion’s roots are thousands of years old. The establishment of property rights, water rights, all of that.

If human civilization exists, with some continuity with the present, 1,000 years from now, such a list will include the release of fossil carbon in the form of greenhouse gasses by the people of the 19th, 20th, and 21st centuries. That was the event that caused the sea to rise and engulf so much of the fertile land, causing a major (if possibly slow moving) exodus of most of the settled people of the world. In a thousand years, after we’ve either stopped using fossil fuel, or didn’t but just used it all up, people will still be measuring for the rise of the sea that we are causing right now.

I don’t think they will be thanking us.

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26 thoughts on “New Research On The Rising Sea

  1. 14 cm is 5.5 inches.

    5.5 inches of sea level rise for the entire 20th century.

    Five feet of sea level rise by 2100 would indeed be a problem.

    But 25 cm (about 10 inches) by 2100 would not be a very big problem (in my opinion).

    I bet you a quarter that we don’t get between 130 and 150 cm of sea level rise by 2100.

    We will get more snow than expected, and it will add mass to Greenland and Antarctica, or water to lakes and ground water, to offset these “the sky is falling” projections.

    Just a guess on my part – but I am willing to put money behind my bet.

    I am even willing to escrow my quarter, because I will very likely die before 2100.

    Any takers?

  2. RickA: “5.5 inches of sea level rise for the entire 20th century.”

    .. and increasing at an astounding rate not seen in the past 55,000 years or more.

  3. “I don’t think they will be thanking us.”

    Good thing we will all be dead, considering the utter horror life will be in the near future because of us. Communities are already fleeing human-caused sea level rise.

    Estimates vary widely on how much infrastructure is already at risk from sea level rise: from 20 trillion to 60 trillion right now. By year 2100 it’s estimated to be from 50 trillion to 120 trillion. That includes hospitals, air ports, military bases, roads, bridges, marinas, towns, cities, power plants, sewage treatment plants, oil refineries, universities, schools, libraries, hotels, and other businesses. And that cost is a tiny fraction compared to lost agriculture and lost fresh water due to sea water incursion— rendering the land much harder to produce food.

    The cost of human-caused sea level rise has already been staggering. I’m very glad I will be dead soon so that I don’t have to face people being born now and explain why we did this to them.

  4. Could you comment, or tell me where to look for a summary, on the whole permafrost melting and releasing methane contribution? I tend to be a bit haphazard in my reading on climate change as I find it so alarming, but I do want to be informed.

  5. It doesn’t even that take much of a sea level rise to be a problem in some places. For example, Miami, which is where I grew up (my parents moved away about a year before Hurricane Andrew), will have to be abandoned sooner or later, and it could happen during my lifetime. Much of the area is low-lying–anything more than about 2 m above 20th-century sea levels is high ground, by local standards–and routine flooding is already occurring in some neighborhoods. Thanks to the geology of the area, you don’t have to wait for full-on inundation for your neighborhood to become uninhabitable: the bedrock is porous limestone, so sea water can come in through the ground, not just over it. Which will make obtaining drinking water problematic. Not to mention storm surges. Miami’s city center has not had a direct hurricane strike since 1965 (Andrew primarily affected the southern part of Miami-Dade County), and given Florida’s real estate history, I wouldn’t bet money that any of that post-1965 infrastructure is adequately hurricane-proofed.

  6. Eric, yeah, to add to that, the sea does not merely go up, it goes across. If you stand 50cm above the high water line and imagine the sea rising to touch your feet, you also have to imagine that the sea will erode the land beneath your feet and actually extend behind you. The amount of horizontal transgression depends on the substrate. In a place like florida (or Bangladesh, or many other places) that will be quite a distance.

    Look at this picture of the beach in florida:

    See that “high” part off to the left? that is, effectively, the sea cliff or bench, and indicates the amount of vertical removal of material that accompanies a given sea level.

  7. I am even willing to escrow my quarter, because I will very likely die before 2100.

    Thank you, RickA, for this nice summary of why you are such an amazing dick about climate change.

    1. Brainstorms: “RickA: Murdering babies to protect his lifestyle…”

      Most of the babies have been and will be brown, so it doesn’t matter. And besides, it’s the “pre-born” that matter: the post-born don’t matter.

  8. What an interesting set of problems for future engineers to tackle! Rising sea levels,eroding shorelines and larger storm surges all mean more flooding is in store for people in the future. Seawater infiltration into groundwater means decreasing volumes of potable groundwater along coastlines. And what do you do with coastal nuclear plants? Or coastal fossil power plants? Municipal sewerage below sea level will be a very very interesting proposition for future engineers. There are just so many really interesting problems that will need solving. Oh to be born more recently so I could work on some of them!

    Actually, I’m an optimist about all of this. Really.. Since our current almost inevitable direction seems to be to just keep polluting our environment with greenhouse gas, petrochemical toxins, and long lived plastic detritus, I’m thinking that at some point we are going to need to just learn to go with the flow or get drowned.

    So now, rather than be upset by all of this, I am proposing that we embrace the new aesthetic. Let’s all sign on to “Develop Till You Puke” and nominate Hair Trump to be our furrier. Garbage is no longer to be viewed as ugly. It is a sign of prosperity. Constant plastic on the beach is no longer detritus; it is managed biome-transformation. The beach on your formerly high and dry plot of land in the foothills will now be coastal value enhancement. Missing sea life is no longer famine inducing; it is obesity control. Drought is no longer agriculture destroying; it is agro-challenge. Heat waves are no longer dreaded occurrences; they are environmental sauna-ization! Coastal flooding is no longer the end of civilization; it is marine-civilization building, or aquarization.

    See. All you negative doom conspirators just need to flip your point of view and get with the program! Don’t worry! Be happy!

    [ Oh my. Did I forget to turn off my snark generator…. again……..?]

    1. SteveP: ” […] Oh to be born more recently so I could work on some of them! [….]”

      The joke is on you (erm humanity), because at CO2 levels above ~630 ppmv, cognitive abilities in humans start to decrease— you (we) will be less able to solve the problem as it gets worse. Haw ha haw ha haa hawww! (Hee hee, hahahaha har har hee hee!) The laws of physics have a sense of humor.

      “Garbage is no longer to be viewed as ugly. It is a sign of prosperity.”

      Must like modern pop “music.”

  9. Sea level rise, and so much more:

    ” The combined impact of warming, acidification and deoxygenation are already having a dramatic effect on the flora and fauna of the oceans with significant changes in distribution of populations, and decline of sensitive species. In many cases, the impacts of warming, acidification and deoxygenation are increased by the effects of other human impacts, such as pollution, eutrophication and overfishing.
    The interactive effects of this deadly trio mirrors similar events in the Earth’s past, which were often coupled with extinctions of major species’ groups.”
    Climate change and the oceans – What does the future hold?

    The following abstract is from 2008:

    “The observed increase in the concentration of greenhouse gases (GHGs) since the preindustrial era has most likely committed the world to a warming of 2.4°C (1.4°C to 4.3°C) above the preindustrial surface temperatures. The committed warming is inferred from the most recent Intergovernmental Panel on Climate Change (IPCC) estimates of the greenhouse forcing and climate sensitivity. The estimated warming of 2.4°C is the equilibrium warming above preindustrial temperatures that the world will observe even if GHG concentrations are held fixed at their 2005 concentration levels but without any other anthropogenic forcing such as the cooling effect of aerosols. The range of 1.4°C to 4.3°C in the committed warming overlaps and surpasses the currently perceived threshold range of 1°C to 3°C for dangerous anthropogenic interference with many of the climate-tipping elements such as the summer arctic sea ice, Himalayan–Tibetan glaciers, and the Greenland Ice Sheet. IPCC models suggest that 25% (0.6°C) of the committed warming has been realized as of now. About 90% or more of the rest of the committed warming of 1.6°C will unfold during the 21st century, determined by the rate of the unmasking of the aerosol cooling effect by air pollution abatement laws and by the rate of release of the GHGs-forcing stored in the oceans. The accompanying sea-level rise can continue for more than several centuries. Lastly, even the most aggressive CO2 mitigation steps as envisioned now can only limit further additions to the committed warming, but not reduce the already committed GHGs warming of 2.4°C.”
    On avoiding dangerous anthropogenic interference with
    the climate system: Formidable challenges ahead

    Not too long ago Michael Mann pointed out that our figure for post-industrial warming doesn’t include the warming that occurred before 1850, so instead of having warmed 1°C, we’ve warmed 1.2°C. warming_b_8841534.html

    If this is correct, then it may be that we’re committed to warming of at least 2.6°C.

  10. I will very likely die before 2100.

    We are fortunate that history will end when RickA dies or in 2100, whichever is sooner.

  11. Desertphile #15 Let’s see,if I’m not mistaken, the level of carbon dioxide in the atmosphere has been pretty close to around 285 ppm in the entire time when humans evolved their current physiology. And now, we are pushing over 400 ppm in even “pristine” air. Yes, I know that blood is well buffered, but I have a hard time imagining that raising the ambient CO2 level by 40% won’t have some measurable effects on blood pH and blood gases and consequently on every freaking biochemical reaction in our body. It would be fun to let people test their abilities in air which has been artificially adjusted back to a more normal 285 ppm. I wonder how long it will be before some entrepreneur does just that; offer clean air for stressed out moderns to breath. Oh wait. I think they already have been doing something like that in Japan for years; selling oxygen at kiosks.

    Anyway,maybe the carbon dioxide induced diminution of human cognition is already beginning. Maybe it is time to stock up on lithium hydroxide air purifiers or something. Just joking of course… but maybe not…

    1. SteveP: “It would be fun to let people test their abilities in air which has been artificially adjusted back to a more normal 285 ppm.”

      There are medical ethics issues involved, even when using prisoners and the inferior races as test subjects (damn it).

      Based on non human tests, applied to humans, I will hazard a guess at the results:

      At around 800+ ppmv humans can expect to see decreased cerebral blood flow and an increased blood acidity, with concomitant impairment of cognitive abilities. At 5,000+ ppmv we can expect to see no humans on the planet. This is a damn shame, because think of how well cannabis will be growing! We need to end marijuana prohibition ASAP, since we are running out of time.

      P.N. Bierwirth (Australian National University) is currently massaging a paper on the subject. I have not read it yet, because I have already had all the bad news I can take for the year…. and it’s still just February.

  12. Albert Einstein: “‘Two things are infinite: the universe and human stupidity; and I’m not sure about the universe.”

    Whoocoodanode that ol’ Albert knew RickA?

  13. Yet another confirmation that:

    – There was no ‘MWP’ as warm as or warmer than the present

    – Modern SLR is unprecedented in at least 2ka

    – The SLR boulder is now rolling down the mountain

    – Millennial SLR is almost certainly locked in

    – Ice sheet dynamics are likely / very likely to hold extremely unpleasant surprises in store for increasingly beleaguered future generations

    – ‘Sceptics’ are utterly resistant to constructive dialogue and actually learning about the science

  14. SteveP – humans already live in places where CO2 concentrations fluctuate well above the average ambient level in the clean places like Mona Laua or Cape Grim where measurements are made.

  15. At the peak of the last Ice Age the weight of ice on N America
    pushed the continent down on its northern edge. It was mantle deformation as much as ice formation that resulted in the exposure of the Bering bridge. This illustrates the uncertainty that complicates calculations. When the ice is removed from the continents the weight loss must be balanced by an equivalent weight gain in
    The global ocean. Mantle rebound here results in mantle depression there. As Antarctica and Greenland rebound the global oceanic crust relaxes. The basins get deeper. The problem arises because no one knows if rebound and relaxation occur at the same rate though it seems unlikely.

    1. Lb

      I discuss this in the post. It is not the case that no one knows how this works. This, as discussed in the post, has been the subject of research for about 60 years.

  16. All this talk without the evidence that the rate of sea level rise is related to fossil fuel emissions or that it can me moderated by reducing emissions.

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