The inevitability of sea level rise

Ben Strauss of Climate Central has considered the different possible future pathways that society might take and computed which US cities are at risk in the long-term. He poses the question as to what year, if we continue with greenhouse emissions at current rates, we will have caused an inevitable sea level rise that puts certain cities at risk.

According to his analysis, within the next few years Miami in Florida will be committed to eventually lie below sea level, while our future actions can still decide on whether we want to one day give up cities such as Virginia Beach, Sacramento, Boston, Jacksonville or New York City.

This is a decision society has to take for future generations. We will need to adapt to climate change in any case, but some things we will not be able to adapt to. Society needs to decide whether we want to give up, for example, the Tower of London, or to put the breaks on climate change so that we don’t have to.

Weblink: The New York Times has a good current article on this issue.

Anders Levermann is department head at the Potsdam Institute for Climate Impact Research, Germany

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198 comments on this post.
  1. Kevin McKinney:

    Thanks for a succinct and clear article. I was recently asked “How much time do we have?” (To do what was not specified!) This adds another dimension to the answer.

  2. Dan Cole:

    Let me begin by saying that is the best site on the web for scientifically accurate information about climate change. With respect to this posting, I do not question the findings of the studies the author cites, and I am convinced that sea level rise is a major problem that will require very expensive adaptation (not possible for all places).

    Having said all that, the author goes too far in suggesting that: (a) because GHG emissions remain in the atmosphere for a very long time, they commit us to a certain extent of sea-level rise over the course of up to 2,000 years; and (b) “Society needs to decide whether we want to give up, for example, the Tower of London, or put the brakes on climate change….”

    There is no warrant for the author’s implicit presumption that no technological innovations over the next 1,000 years could alter the relationship between carbon in the atmosphere and sea-level rise. Already, we have technology to reduce the terrestrial effects of GHG emissions by inserting sulfur aerosols (or other reflecting particles) into the upper atmosphere. (Whether doing so is a wise policy remains, at this point, a contested issue.)

    The author’s other implicit assumption that there is no feasible way to protect a coastal (or tidal) city from the effects of sea level rise is simply false. Amsterdam has been sitting below sea level for centuries, and yet we haven’t had to “give up” on the Rijksmuseum. Whether Amsterdam can technologically work its way around another few meters of sea-level rise, remains to be seen. This is not to say that coastal areas won’t suffer grievously from climate change; sea walls may protect a city, but only at the cost of inundating other (presumably less valued) coastal areas.

    The most important point, however, is that climate scientists do not make it any easier to convince skeptics (let alone deniers), when they draw the more dire, catastrophic conclusions from every study. It is far better to be parsimonious and limit conclusions to what can reasonably be inferred from the science, and leave the hyperbole to the “talking heads.”

  3. Anders Levermann:

    @Dan H,

    the Antarctic projection were obtained from the simulation of the past 5 million years by David Pollard and Robert De Conto published in Nature in 2009. The increase in snowfall on Antarctica is very likely to happen in a warming world. However what was not accounted for (and explicitly stated but not often recognized) in the last IPCC report is that the IPCC did not account for dynamic ice discharge from Antarctica. Now, in contrast to Greenland this is the strongest ice-loss process from Antarctica (currently about 99% of the ice loss) and thereby needs to be accounted for. In these simulation it is accounted for.

    I hope that helps.

  4. Kevin McKinney:

    “There is no warrant for the author’s implicit presumption that no technological innovations over the next 1,000 years could alter the relationship between carbon in the atmosphere and sea-level rise.”

    I disagree. While it is true that one can imagine scenarios which do alter this relationship, the feasibility of *any* of them remains highly dubious. (Especially over, say, the next century, which likely will have the most influence on ultimate sea level rise.)

    Therefore, the presumption made is the most plausible one–hardly an unreasonable inference, nor ‘hyperbole.’

  5. Tony Noerpel:

    Hi Anders

    Thanks so much for this explanation. I’m still puzzled by one thing. The LGM was about 3.5 degrees C colder but sea levels were 120 meters lower. This isn’t explained by the 2.3 meters per degree C. Is the explanation simply that the sea level relationship to temperature is non-linear and the slope of 2.3 meters per degree just happens to correspond to the current climate?


  6. prokaryotes:

    A documentary from 2010 still good, with many expert opinions explored this topic.

    Changing Sea level budget and Semi-Empirical models

  7. Kevin McKinney:

    Ben Strauss’s analysis in PNAS takes the form of a commentary–are PNAS commentaries considered fully peer-reviewed, by the way?–based upon another recent analysis, cited as:

    Levermann A, et al. (2013) The multimillennial sea-level commitment of global warming. Proc Natl Acad Sci USA, 10.1073/ pnas.1219414110.

    The commentary PDF:

    [Response: These commentaries aren’t peer reviewed as far as I know. –eric]

  8. prokaryotes:

    @Dan H,

    limit conclusions to what can reasonably be inferred from the science

    I disagree, and The futility of “just the facts” climate science is a recent article which explores why.

  9. Victor Venema:

    Isn’t the term “commitment” a bit too strong?

    The half life of the CO2 we emit is about 200 year, right. So the “commitment” would only be for the coming centuries and not indefinite, which the term suggests, or for 2000 years.

    I would not be surprised if at a certain time renewable energy is so much cheaper as fossil fuels, that the greenhouse gas emissions will go down to almost zero again. Thus maybe it would be a good (additional) alternative scenario to assume that the temperature will peak and not stay constantly high for 2000 years.

    [Response: The half life of CO2 isn’t really 200 years. It’s not a simple exponential function. About 10% of what we produce will be in the atmosphere for tens of thousands of years. See David Archers various publications on this, and his early RealClimate post, here. –eric]

  10. Ronal Larson:

    Anders. Thanks for the new computations. Could you comment on the possible validity of Dr. Jim Hansen’s view that we may see exponential behavior – doubling every decade or so.

  11. richard pauli:

    Thank you for a superb summary. Your last statement that we must decide – is key.

    We don’t yet have universally widespread education/information, but certainly rising seas will deliver the message better than any other communication medium. Species-level wisdom must precede decision making. And humans have never globally unified on any course of action. Our first task is to decide to decide. This may entail an evolutionary leap in species commitment to survival.

  12. Gene Hawkridge:

    I think a key question is how much sea level can rise. My own back-of-the napkin estimate is 60 m, based on estimated ice volumes in Antarctica and Greenland alone. This does not account for thermal expansion, nor changes in the Earth’s mass distribution that are already recognized to be taking place. So, some places won’t get this much sea level rise, and others, possibly much more.
    If we were seeing some real, significant progress in curbing carbon emissions, perhpas there would be no cause for alarm. The fact is, however, the rate of emissions is still increasing. In the US, the actions of a completely irresponsible oil and gas industry that peddles its misinformation to the poorly-educated voter masses, makes doing anything significant unlikely in any near-term scenario.
    Amsterdam and the Dutch have a commendable record of holding back the sea, but a few cm per century is an order of magnitude less than what they need to deal with in the future.
    I’ve seen little in the way of realistic political action anywhere in the US, and little prospect of this changing until disaster becomes too obvious for the denialists to maintain any credibility.
    So, we shouldn’t be alarmist? I have grand children; they will have to live with the consequences of my generation’s failure to act. It will be very expensive and very dangerous. It will result in economic and social instability. I am and remain alarmed, and I do not agree with those who call for sugar-coating the message about our future.

    Gene Hawkridge
    Kenmore, WA, USA

  13. patrick:

    @3 Very sorry about sulfur aerosols. They don’t stay up that long. They have to be continually replenished. Every sort of magic trick is going to be sold for climate change. ‘Technology’ is way too good a word for it.

    Beyond that, “the…implicit presumption[s]” for which “there is no warrant” are all yours, sorry to say.

    There is some remediative tech that can help, but it’s not about messing with the atmosphere or the oceans. Remediative tech should be land-based. It should be easy to test, audit, reverse, and discontinue.

    The technologies for preventing sea-level rise (beyond what’s already in process) are known, or clued-in. They are methods of generating electricity that don’t burn fuel and don’t use, or cycle, huge amounts of water.

    Non-dependence on toxic waste is also important.

    Ponder what tech can do with that, starting now, over the next 1000 years, please.

    Fixing it backwards is not an answer, it’s a panic.

    The best way to fix it is to prevent it. The best way to fix it is to prevent it. The best way to fix it is to prevent it.

  14. deconvoluter:

    Not enough attention has been given to the long term. A thousand years is not so long; many European cities have buildings which are older.

    I remember being struck by this comment in the IPCC TAR of 2001

    Ice sheets will continue to react to climatic change during the next several thousand years, even if the climate is stabilised. Together, the present Antarctic and Greenland ice sheets contain enough water to raise sea level by almost 70 m if they were to melt, so that only a small fractional change in their volume would have a significant effect.

    Models project that a local annual average warming of larger than 3°C, sustained for millennia, would lead to virtually a complete melting of the Greenland ice sheet with a resulting sea level rise of about 7 m. Projected temperatures over Greenland are generally greater than globally averaged temperatures by a factor of 1.2 to 3.1 for the range of models used in Chapter 11. For a warming over Greenland of 5.5°C, consistent with mid-range stabilisation scenarios (see Figure 26), the Greenland ice sheet is likely to contribute about 3 m in 1,000 years. For a warming of 8°C, the contribution is about 6 m, the ice sheet being largely eliminated. For smaller warmings, the decay of the ice sheet would be substantially slower (see Figure 27).


    Can you imagine how the nuclear industry would be treated if they argued that it was unnecessary to secure nuclear waste for as long as a thousand years?

  15. Rob Quayle:

    This work impelled me to do my own comparison of global sea level (CSIRO & U Colo) vs global surface temperature (NCDC), 1880-2012. Empirically, the relationship is about 2.1 m per deg C. Quite close to this blog entry’s 2.3 m per deg C. I’ll be glad to email a copy of the work if you like.

  16. Hank Roberts:

    The comments about technological innovation saving us miss the point; we are not the world. Starting something we don’t know how to control and aren’t smart enough to quit making worse, trusting some Deus Ex Machina answer will appear, is tragedy.

  17. Killian:

    We are currently at 0.8C or 0.9C above pre-industrial.

    We are thus committed to a minimum of about 1.82M more SLR.

    In reality, we are committed to temps thirty years from now and that level of SLR PLUS any increased temps due to emissions from this point forward.

    That’s an easy 3M SLR, I’d guess.

    I’m certain the recent findings by Box and others as to the ice sheets being more dynamic than thought will cause upward revisions in terms of how quickly SLR can occur.


    Query: I’ve seen this questioned asked exactly zero times, but it is the key question, imo. Were we to get CO2 back to 270ppm within 50 – 100 years, to what extent would that reduce future SLR? Said another way, what is the thermal response of ice sheets to reducing CO2 significantly?

    We may be seeing a hysteresis in the Arctic with the very ice reduction in question shifting seasons so much that ice formation is pushed well into winter and ice melt is pushed consistently into March. The changes to the Jet Stream seem to be bringing a consistent positive Arctic Oscillation and more cloudiness and cool temps this summer and last summer which might be slowing ice loss. (Last year’s melt would be partially due to thermal inertia in the Arctic with that abating somewhat this summer in this scenario and, were that trend to continue, it would possibly continue into future summers and possibly lead to a period of relative stability at this new 2012-2013 level until thermal inertia in the oceans overpowered this or the system reverted to pre-Jet Stream jerrymandering.)

    Anywho… if we can reduce CO2 to pre-industrial, what is the effect on the ice sheets?

  18. AJ:

    I’m having trouble understanding why a model would predict a decrease in sea level rise due to antarctic ice melt as temperature increases, even “temporarily”, as illustrated in Figure (d) at ~3.9 C. The PNAS paper indicates these are physical models, not observations. I would expect all contributions to be smooth functions, like (a) (b) and (c).

    Also, why does the PNAS paper this post summarizes have a completely different effect for the Greenland ice sheet, indicating a dramatic rise of 6 meters at just 1.5 C? This also dramatically changes the overall value predicted in (e) to ~15 m at 4 C.

  19. AJ:

    Re. my second question in the previous post, I see now that the figure here is the commitment for the next 2,000 years, corresponding to Figure 2 in the PNAS paper, as opposed to the reconstruction in Figure 1.

  20. S.B. Ripman:

    This from the 8/12 NYT article on locked-in SLR:
    “Benjamin Strauss and his colleagues at Climate Central, an independent group of scientists and journalists in Princeton that reports climate research, translated the Levermann results into graphical form, and showed the difference it could make if we launched an aggressive program to control emissions. By 2100, their calculations suggest, continuing on our current path would mean locking in a long-term sea level rise of 23 feet, but aggressive emission cuts could limit that to seven feet.”

  21. patrick:

    With no intention to distract, I note, on the subject of SRM (raised above):

    “Remember, in this new era, nature is us.”–Nobel Laureate Paul Crutzen “Living in the Anthopocene”

    “A contemporary giant of science, the Nobel laureate Paul Crutzen, has rekindled the SRM debate in 2006 through an essay on stratospheric sulfur injection (17). However, he has consistently argued then and ever since that such a climate-engineering scheme would be implemented out of despair only, that is, if the establishment of any “conventional” climate-protection measure (like a worldwide cap-and-trade system for greenhouse gas emissions) failed. …

    “On closer inspection SRM [‘solar radiation management’] exhibits traits of MAD [‘mutually assured destruction’]. …” –John Schellnhuber

    “Geoengineering: The good, the MAD, and the sensible.” Published online 12 Dec 2011, doi: 10.1073/pnas.1115966108 PNAS December 20, 2011, vol. 108 no. 51

    “Last, efficiency and renewables will achieve something that [ex-post-fixit] approaches do not even care to consider: laying the foundations for a sustainable global energy supply system that (i) can virtually exist forever, and (ii) offers more equitable opportunities for the developing world…

    “In essence, humankind should avoid betting on the fabrication of a silver bullet for shooting climate change. Our world does not need SRM…in the first place, but rather a novel way of going MAD: ‘mutual assured decarbonization.’ ”

    [In the last quote I have substituted “ex-post-fixit” for the “g”-word. ‘Gee-oh!’ works, too, I think. I’d like to keep the “g”-word, itself, for things worthy of the name–involving forethought and foresight.]

    John Schellnhuber, PNAS profile:

    To exit an addiction, or a reversible illness, it’s helpful to ask: what do you want to do for the rest of your life?

    To exit an addiction to types of progress that are like home run records made on steroids, it’s helpful to ask: what do you want to do for the next 2000 years, to start with?

    Science on the long-term effects of present action is sobering and very healthy, if you let it in.

    Thank you, Anders Levermann. On the excellent NYT article, my luck’s holding, because I said: Justin Gillis hasn’t confused anyone yet.

  22. Jan Galkowski:

    Two comments on comments.

    (1) Dan Cole urges faith in technological innovation. I acknowledge we could get clever, but the prospects are truly daunting, not only because of the reliance upon as-yet-to-be-developed methods, but because the Earth is a big place, and ANY method will need to scale, cheaply in cost and cheaply in energy usage. So, there are THREE challenges, not just the science: technology, cheapness of energy use, and cost for global build-out, while the economies of the world are driving towards zero emissions. Realize, to make 450 ppm it’s estimated the globe needs to start reducing its emissions by 2020, not just its rate of emissions. And there will be economic costs to do this, in addition to deploying the Magical Technology to fix the coupling between atmospheric CO2 and sea-level rise. It’s not only about energy, it’s where the energy goes. Sea level rise has multiple components, with ice melt being long term big, as the article says, but thermal expansion having a significant piece, too.

    (2) “Were we to get CO2 back to 270ppm within 50 – 100 year” … Not sure but it sounds like Killian may be confusing emissions with accumulation. Might reduce emissions, but drawing down CO2 means carbon dioxide REMOVAL (not capture and sequestration), irrespective of what is done with aerosols. For global deployment and assuming it can be done at all, that’s priced at trillions of U.S. dollars per annum. The contingency is that this needs to be done at an ENERGY COST for manufacture and operation which does not significantly affect emissions, which need to be rapidly approaching zero for this to make sense. In net, we need to run negative emissions for a time.

    Reference: “Atmospheric Lifetime of Fossil Fuel Carbon Dioxide”, Archer, Eby, et al, Annu. Rev. Earth Planet. Sci. 2009. 37:117–34. Pertinent finding is that 20%-35% of atmospheric CO2 remains for 3000-7000 years. The remainder equilibrates with oceans on a scale of 2-20 centuries.


  23. David B. Benson:

    Killian @18 — Reducing CO2 to pre-industrial concentrations would eventually lead to the formation of as much ice as was present then.

  24. Hank Roberts:

    Personally, I’m changing my prediction to imagining the icecaps behaving like ‘shatterproof’ glass — fracturing into zillion of little blocks.

    Say some summer day, some critical number of surface ponds suddenly disappears, having melted through, raising the bottom temperature to where it lets other cracks melt through, and drain, lather rinse repeat — and the ice caps !sproing! break up along whatever stresses existed, turning all of the ice all at once into piles of ice cubes, which then rush to the ocean.

    “Walk faster, the ocean’s rising all of a sudden….”

    I’ll save that for my big scary blog, if I ever start one. Or a novel ….

  25. Jim Larsen:

    1 Dan H said, “Many other predictions claim that much greater warming would need to occur before Antarctica ceases to accumulate ice”

    You’re confusing East Antarctica with Antarctica. Antarctica is already losing ice.

  26. Killian:

    In net, we need to run negative emissions for a time.

    Obviously, so that isn’t the question I was asking. Assume everything else, regardless of how achieved, and get to the bottom line: If we reduce to 270 ppm in 50 – 100 years, and stay there, what is the effect?

    David B. Benson says:
    15 Aug 2013 at 7:03 PM

    Killian @18 — Reducing CO2 to pre-industrial concentrations would eventually lead to the formation of as much ice as was present then.

    Again, obviously. Didn’t realize the basics would confuse.

    The context of the article was TIMING. So… bearing the context in mind, reduce in that time frame, stay at that level, what is the result in terms of hysteresis on melt of the various forms of ice and rebuilding those various masses, thus eventually lowering of SLR after what peak?

  27. adelady:

    and the ice caps !sproing! break up along whatever stresses existed, turning all of the ice all at once into piles of ice cubes, which then rush to the ocean.

    That’s more my suspicion at the moment. We have no history, no data, no anything at all to believe that conditions we’ve not seen before will simply mean more and faster of what we have seen before.

    Paleo results tell us mainly how things finished up after these processes had done their work, they don’t give us too many hints of what can happen in a few decades or a couple of centuries during the process itself. And the collapse of summer sea ice within just one decade tells us that we really would be a bit silly if we relied too strongly on our projections based on historical data.

    Whatever happens, I very much doubt it will simp0ly be more of the same, but a bit faster, even if it’s not this particular scenario.

  28. MARodger:

    AJ @19.
    The reason for the dips in graph d is probably due to projected increases in snowfall over Antarctica.

  29. Nick O.:

    @21, S.B.Ripman:
    “… By 2100, their calculations suggest, continuing on our current path would mean locking in a long-term sea level rise of 23 feet, but aggressive emission cuts could limit that to seven feet.”

    SEVEN FEET?! Even after ‘aggressive emission cuts’? Not much hope for central London, then, or indeed for many British seaside towns and villages. Even a 1 foot rise would entail problems in many of our coastal areas.

    On another point, but related to this topic, and for someone who is a scientist by not a climate scientist. My v. rough understanding of the present temperature trends is that warming appears to have “stalled” for the time being (with respect to air temps, anyway), but since the heat must still be going somewhere, it’s probably going into the oceans instead. Thus, the rate of sea level rise over the next decade or so will probably be somewhat faster than formerly predicted by the IPCC/whoever, owing to more thermal expansion. Is that about right?


  30. Chuck Hughes:

    What are the chances of the oceans becoming anoxic to the point that H2S or Hydrogen Sulfide becomes a serious problem for humans in this century?

  31. mitch:

    The chances are essentially zero that the oceans will become anoxic. There is plenty of deep circulation to feed oxygen down.

  32. Pat Saunders:

    [correction] The executive summary of the 2007 IPCC report said that “Global sea level was likely between 4 and 6 m higher during the last interglacial period, about 125 ka, than in the 20th century. In agreement with palaeoclimatic evidence, climate models simulate arctic summer warming of up to 5°C during the last interglacial. The inferred warming was largest over Eurasia and northern Greenland, whereas the summit of Greenland was simulated to be 2°C to 5°C higher than present. This is consistent with ice sheet modelling suggestions that large-scale retreat of the south Greenland Ice Sheet and other arctic ice fields likely contributed a maximum of 2 to 4 m of sea level rise during the last interglacial, with most of any remainder likely coming from the Antarctic Ice Sheet.”
    What are the PAGES scientists saying now.

  33. Anders Levermann:

    @Dan Cole (comment #3)

    Please consider that we are talking about adaptation of infrastructure and cities not about computer chips and that 2000 years is an upper limit for the time it takes for this too occur. Sure, we cannot even imagine the technology that we will have at hand in the far future, but again Hamburg is a coastal city and it is more than 700 years old. Even if you unplug it and move it to another place it is not the same as it was before, neither will it be the same if we build a 3 meter wall around it. Cultural heritage, infrastructure and the like are inert and big.

  34. John Pollack:

    adelady @28 We do have some paleo evidence that nearing the height of the last interglacial about 121k b.p., there was a rapid sea level rise of 2-3m “on an ecological timescale” i.e. faster than coral in a sheltered lagoon could grow upward to keep up with the rise. This occurred when sea levels were already about 3m above present values. See for more information.

  35. Chuck Hughes:

    Asteroid strikes get all the coverage, but “Medea Hypothesis” author Peter Ward argues that most of Earth’s mass extinctions were caused by lowly bacteria. The culprit, a poison called hydrogen sulfide.

  36. Hank Roberts:

    > Assume everything else, regardless of how achieved

    No change in aerosols?
    No change in black carbon?
    No change in CO2 dissolved in oceans?

    Or do you mean, put everything back 200 years except the current sea level and ask which way it’d trend and how fast and where would it end up?

    Connections are too complicated to answer your simple question as posed.

  37. Mal Adapted:


    The chances are essentially zero that the oceans will become anoxic. There is plenty of deep circulation to feed oxygen down.

    I wouldn’t be so quick to dismiss ocean anoxia as a possible consequence of AGW, albeit one that would take thousands of years to develop. I’ve just finished reading Peter Ward’s Under a Green Sky. He makes a convincing argument that the Permian-Trassic mass extinction (and probably other extinction events) was caused by global warming from GHGs released by volcanic eruptions, which shut down deep circulation in the oceans, resulting in multiple episodes of ocean anoxia, and the release of toxic quantities of H2S into the atmosphere.

  38. Mal Adapted:

    Me: “Permian-Trassic” – that’s “Permian-Triassic”, of course

  39. Thomas Lee Elifritz:

    The chances are essentially zero that the oceans will become anoxic. There is plenty of deep circulation to feed oxygen down.

    Excuse me, but the loss of our ice sheets, the warming and overturning of our oceans and ocean anoxia is the inevitable result of this phenomenon if left unabated.

    It’s just a matter of time.

  40. Fred Moolten:

    @Victor Venema (10) – Excess atmospheric CO2 doesn’t have a single half life, but subsides at declining trajectories as CO2 is absorbed and buffered in the upper ocean (about half in 1-2 centuries), equilibrated with the deeper ocean and buffered by carbonate dissolution, followed by carbonate restoration through weathering of terrestrial rocks – the last processes requiring thousands to hundreds of thousands of years. If CO2 emissions ceased, all other things equal, temperature would not remain absolutely steady, but would vary little on centennial scales since the declining warming effect of the excess CO2 would be largely balanced by the slow surface warming from the thermal inertia of the oceans for an extended interval. For a useful analysis, see the PNAS paper by Susan Solomon et al at Irreversible Climate Change.

  41. Hank Roberts:

    > adelady says:
    > 16 Aug 2013 at 12:06 AM
    >> and the ice caps !sproing! break up along whatever stresses
    >> existed, turning all of the ice all at once into piles of
    >> ice cubes, which then rush to the ocean.
    > That’s more my suspicion at the moment.

    That scenario was poking fun at fantasy-climate-blogs.
    Please don’t take this kind of goofiness seriously.
    Fantasy disasters play purely to people’s fears.
    Look for citations to science journals. Read. Think.
    If you think you understand it, cite to and blog about what you understand.

  42. mdenison:

    The 2012 paper from Foster and Rohling suggests that the paleo record implies a sea level rise of about 14m for doubled CO2 whereas your work implies about 7m.

    Could you comment on how you think your work squares with that of Foster and Rohling?

  43. Patrick Mazza:

    So what about photosynthesis? If the removal goal is 100 ppm that equals 210 GTC. Currently around 2200 GTC are held in soils and plants. Many ecosystems are carbon-depleted due to human activities such as deforestation, conventional agriculture and development. More carbon can circulate though forests with reforestation, afforestation and longer-rotation management of timber lands. More carbon can circulate through farm soils through no-till, residue management, returning organic carbon to soils, cover crops. Wetlands restoration can rebuild carbon-rich ecosystems. An added bonus is that these land management changes improve resilience of forests, agriculture and ecosystems under increased climate extremes. The challenge is to build economic and policy models that provide incentives for change. Perhaps a devotion of a certain percentage of eventual carbon revenues can contribute, supporting carbon-negative practice changes (as opposed to carbon-neutral offsetting). We can hope that technological CO2 removal modalities in development by scientists such as David Keith prove economical and feasible. But photosynthesis is available now, and can be unleashed for CO2 removal by known practice changes. Any problems in this picture?

  44. Rob Quayle:

    Correction to comment 16: Empirical sensitivity seems to be about 212 mm per deg. C.

  45. bibasir:

    Killian @18 — Reducing CO2 to pre-industrial concentrations would eventually lead to the formation of as much ice as was present then.

    I’m not so sure about that. That ice was formed during the last glacier period. It has been melting for the last 11,000 years, so why do you think it would reform?

  46. Lennart van der Linde:

    mdenison #43,

    Foster & Rohling (2013) say:
    “Given the present-day (AD 2011) atmospheric CO2 concentration of 392 ppm, we estimate that the long-term sea level will reach +24 +7/−15 m (at 68% confidence) relative to the present.”

    Where in the paper do you read that they suggest the paleo record implies about 14m rise for doubled CO2?

  47. Hank Roberts:

    where do you get ” It has been melting for the last 11,000 years”?
    Have a look at
    the typical ice age ends suddenly (as one did about 11,000 years ago); then, typically, a very slow cooling progresses. We interrupted that, this time.

  48. Dan Cole:

    For those who (incorrectly) observe that I have too much faith in technology, when I was merely questioning Anders’ complete neglect of the possibility, I offer the following quote from Tom Schelling: “Seventy years ago we did not have electronics, radioisotopes, nuclear energy, antibiotics, genetics, satellites, or even plastics—it was all silk, rayon, isinglass, and celluloid. How do we possibly foresee seventy years from now?” Thomas C. Schelling, “What Makes Greenhouse Sense?” Indiana Law Review 38:581-593 (2005), at 586.

    In any case, we should not worry so much about rich cities as millions of poor Bangladeshis engaged in subsistence agriculture on floodplains that will be inundated long before any rich city disappears beneath the waves.

  49. Hank Roberts:

    > Tom Schelling
    Same point from John Nielsen-Gammon, but
    Consider that we’ve overshot carrying capacity
    So we may not have more of this lovely tech progress
    going on forever.
    Stein’s Law may apply: If something cannot go on forever, it will stop.

    That’s the worry — that we’ll leave a generation or two in the future without the lovely surpluses and freedoms we got by consuming the Americas and most of what lives in the oceans, did that over a period of a couple of centuries, all that lovely free lunch, and now it’s almost all gone.

    What will we do next? When the cornucopian approach fails? You can find Catton’s _Overshoot_ many places; here’s a quote from one online excerpt — he’s describing the lesson that could have been learned from the Great Depression:

    “… With breakdown of the mechanisms of exchange, various segments of a modern nation had to revert as best they could to living on carrying capacities again limited by locally least abundant resources, rather than extended by access to less scarce resources from elsewhere. Although scope reduction hurt everyone, rural folk had local resources to fall back upon; urban people, in contrast, had so detached themselves as to have almost ceased to recognize the indispensability of those resources. For reasons we shall examine in a moment, economic hard times hit the farms sooner than they hit the cities, but in the final scope-reducing crunch the farmers turned out to have an advantage sufficient to interrupt a clear trend of urbanization.
    No Fairy Godmother

    The Depression also interrupted the advance of industrialization and its attendant occupational diversification of the population. With hindsight, that interruption becomes an opportunity to bring the previous diversification into ecological focus.

    An ecological perspective enables us to see pressure toward niche diversification as the natural result of the overfilling of existing niches. Among non-human organisms, this pressure leads eventually to the emergence of new species. Among humans it leads through sociocultural processes to the emergence of new occupations …

    … In nature, overfilling of old niches can result in massive death. Many organisms fall by the wayside in the march of speciation. Among human organisms the principles hold, but the process is moderated because humans are occupationally differentiated by social processes rather than by biological processes. Ostensibly, when old niches become obsolete, we can retrain ourselves for new roles. So, for Homo sapiens, overpopulation and death are avoidable results of niche saturation. The avoidance is not easy, however, and retraining for new niches can be traumatic.

    An ecological perspective thus heightens the significance of a classic sociological study that clearly showed how unlikely it is, even among members of the relatively flexible and plastic human species, that re-adaptation to new niches (as old ones close up) will occur easily or automatically.

  50. Jon Kirwan:

    We have learned a lot about the north polar ice cap. We are learning a lot more about Greenland, right now. But it seems to me that we are far behind where we’d like to be in understanding Antarctica — both West and East. I recall a July 2013 AGU youtube discussion about just how little predictability the state of knowledge today provides for the West. And I believe this also applies equally to the East.

    Just this last week or two I have read about paper on Antarctica that perhaps highlights important changes in prior understanding, as the following link from the University of Washington discusses:

    Reading between the lines, I take this as a segue for some pretty serious questioning of prior estimates, even relatively recent ones. I do understand that this is a new report and it takes time for others to search out problems, do further research, etc. But it does give me pause, too.

    It’s potential re-alignments in our knowledge like this that give me pause when reading relatively conservative (assume 0th order [no change, just constant] when you have no information, assume 1st order [linear] when you have vague idea about local trend lines, assume more ONLY if you have good theory AND lots of experimental result) estimates, which I see (despite phrases as “quasi” linear) essentially as a relatively ignorant linear assumption absent better knowledge.

    In the meantime, I’m not assuming that current quasi-linear projections are anything more than reflective of how little we really know.

    Seeing quasi-linear models of ice does NOT exactly comfort me. It makes me think, instead, we have a long ways yet to go.