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What drives uncertainties in adapting to sea-level rise?

Filed under: — stefan @ 17 March 2016

Guest article by Sally Brown, University of Southampton

Let me get this off my chest – I sometimes get frustrated at climate scientists as they love to talk about uncertainties! To be sure, their work thrives on it. I’m someone who researches the projected impacts and adaptation to sea-level rise and gets passed ‘uncertain’ climate data projections to add to other ‘uncertain’ data projections in my impact modellers work bag. But climate scientists do a good job. Without exploring uncertainties, science loses robustness, but uncertainties in combination can become unbounded and unhelpful to end users.

Let’s take an adaptation to sea-level rise as an example: With increasing scientific knowledge, acceptance and mechanisms that would allow adaptation to potentially occur, one would think that adaptation would be straight forward to implement. Not so. Instead of hard and fast numbers, policy makers are faced with wide ranges of uncertainties from different sources, making decision making challenging. So what uncertainties are there in the drivers of change, and can understanding these uncertainties enable better decisions for adaptation?

Prior to considering adaptation in global or regional models, or implementation at local level, drivers of change and their impacts (and thus uncertainties) require analysis – here are a few examples.

Between 1901 and 2010, global sea levels rose by 0.19±0.02m, albeit at varying rates and spatial distribution (Church et al. 2013) – these past values (including their uncertainty) are potentially much smaller than those associated with future projections. Whether this precise trend will continue is uncertain, but scientists are confident that sea-levels will continue to rise and accelerate due to global warming

My background is partly in geology, so I often recall the well-known quote referring to Earth’s history ‘the present is the key to the past’ (Hutton / Lyell). In sea-level science however it might be the other way around: ‘the past is the key to the present’. Kopp et al. (2016) recently found that from the late in the 20th century sea-levels have risen faster than in any of the previous 27 centuries. Further back in time again, sea-levels have risen at much faster rates during the end of the last ice age. Past rates of change, if used wisely, provide potential constraints of future projections, together with the many semi-empirical approaches to project future sea-level rise (e.g. Rahmstorf, 2007) which are typically greater in magnitude than those from process based models. Hybrid approaches have also been undertaken (e.g.  Moore et al. 2013, Mengel et al. 2016). Scientific knowledge input into process based models has much improved, reducing uncertainty of known science for some components of sea-level rise (e.g. steric changes), but when considering other components (e.g. ice melt from ice sheets, terrestrial water contribution) science is still emerging, and uncertainties remain high. Still, our understanding has a wide range of projections, particularly for high emissions scenarios as Jevrejeva et al. (2014) illustrates. Given emerging knowledge and changes in uncertainty, this leads me to the question, what are we adapting to, and when could this occur? Is it about 1m of rise by 2100? Or 1.4m?

Planning for sea-level rise does not just depend on how much waters rise, but also how land levels change. Glacial Isostatic Adjustment (GIA) occurs in response to retreating ice from the last glacial period, where around most of the world, land is subsiding at a fraction of a millimetre per year, compounding the problem of sea-level rise. In northern latitudes the reverse is happening – land is rising after being liberated from the mass of the ice sheets, again normally by less than 1mm/yr, but in places over 5mm/yr (Peltier et al. 2015). Land levels also change due to tectonics, natural compaction of soft soils as well as human influences.

I recently researched causes of subsidence in Bangladesh (Brown and Nicholls 2015) and struggled with the uncertainties, data errors, and in some cases, poor science when recording rates of subsidence. In Bangladesh, subsidence can be much higher than GIA – with 10mm/yr being a local norm, rather than an extreme rate. A major cause can be groundwater withdrawal resulting from the needs of a growing population. These factors can be spatially highly variable, even within a short distance. Additionally, rates of subsidence also change with time (Kaneko and Toyota, 2011). Subsidence is common in deltas and projecting relative change (particularly when causes vary or are unknown) remains uncertain.

ganges-india_attila-lazar Relative land level change is extremely important in low-lying delta regions.

When I undertake an impacts assessment, land elevation and population exposed to hazards becomes extremely important. Global elevation levels, such as from the Shuttle Radar Topographic Mission (Rabus, 2003) is an extremely helpful dataset. Elevation data has a resolution of tens of metres, and subject to errors which can mean important coastal features are omitted, such as entire small islands. Similar distribution issues occur with respect to population.

Projecting how population changes – per country and it’s spatial distribution – is an additional uncertainty, particularly as coastal population grows differently to those areas further inland (Neumann et al. 2015). Of course, there are changes in economic growth too – who could have imagined rapid growth seen in Asian cities over the last few decades? Whilst projections of socio-economic change can be made, these still have a wide range of implications in impact assessments and choices over adaptation.

All these factors and many more combine uncertainties resulting in different scenarios of change – each potentially likely to occur. Fed into impacts assessment, further uncertainties arise. But even faced with this, modelling and choosing the type of adaptation itself is uncertain, whether this involves ‘hard’ barriers, such as sea-walls, ‘soft’ protection including sand nourishment, accommodating sea-level rise by raising buildings, or even deliberately retreating from the sea. Furthermore, sea-levels won’t stop rising in 2100 – even under climate mitigation, so adaptation has to be a long-term investment. Nevertheless, engineering reasoning may question the scientific and financial values of adapting newly built infrastructure to sea-level rise over a 100-year timeframe, if the design life is far less than this. Adaptation therefore has to take a flexible modular approach, allowing for uncertainty, rates of change and investment choice. Long-term investment in infrastructure could become a cat-and-mouse game, where monitoring becomes increasingly important leading to reactive adaptation to avoid an unacceptable situation of escalating risk.

With this, adaptation remains a choice or an opportunity which may not be available to all. Better decision making is enabled by making policy makers aware of the wider range of uncertainties, possibilities and options available. This includes how best to apply for and utilise climate change adaptation funds for developing nations, so that intelligent choices can be made to encapsulate uncertainty.


Adaptation is a manner of choice, mixed with local needs

In recent years there has been a push towards climate services to provide forecasts or projections of long-term change to enable adaptation. I think this is a welcome development as it indicates that climate change is becoming more accepted within the international community leading to action. It’s important to remember that climate change is not the only issue and multiple uncertainties exist in other fields that can sometimes be greater than the climate signal alone, leading to deep uncertainty.

So, to answer my question ‘what uncertainties are there in the drivers of change, and can understanding these uncertainties enable better decisions for adaptation?’, perhaps it as apt to quote Albert Einstein: ‘The more I learn, the more I realise how much I don’t know’. The quest to reduce uncertainty (and my frustration!) continues.

Sally Brown is a Senior Research Fellow at the University of Southampton, UK and a member of the Tyndall Centre for Climate Change Research.


Anuar, N. (2015). 20 skylines of the world: then vs now. Accessed August 2015.

Brown, S. and Nicholls, R.J. (2015). Subsidence and human influences in mega deltas: The case of the Ganges–Brahmaputra–Meghna. Science of The Total Environment, 527-528, 362–374. DOI: 10.1016/j.scitotenv.2015.04.124

Church, J.A., Clark, P.U., Cazenave, A., Gregory, J.M., Jevrejeva, S., Levermann, A., Merrifield, M.A., Milne, G.A., Nerem, R.S., Nunn, P.D., Payne, A.J., Pfeffer, W.T. Stammer, D. and Unnikrishnan, A.S. (2013). Sea Level Change. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Stocker, T.F., Qin, D., Plattner, G.-K., Tignor, M., Allen, S.K., Boschung, J., Nauels, A., Xia, Y., Bex, V., and Midgley, P.M. (eds.)). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Jevrejeva, S., Grinsted, A. and Moore, J.C. (2014). Upper limit for sea level projections by 2100. Environmental Research Letters. 9, 104008. DOI:10.1088/1748-9326/9/10/104008

Kaneko, S., and Toyota, T. (2011). Long-term urbanization and land subsidence in Asian megacities: An indicators system approach. In: groundwater and subsurface environments: Human impacts in Asian coastal cities (Taniguchi, M. (ed.)). Springer, Japan.

Kopp, R.E., Kemp, A.C., Bittermann, K., Donnelly, J.P., Gehrels, W.R., Hay, C.C., Mitrovica, J.X., Morrow, R.D., Rahmstorf, S. and Horton, B.P. (2016). Temperature-driven global sea level variability in the Common Era. Proceedings of the National Academy of Sciences of the United States of America. doi: 10.1073/pnas.1517056113.

Mengel, M., Levermann, A., Frieler, K., Robinison, A., Marzeion, B. and Winkelmann, R. (2016). Future sea level rise constrained by observations and long-term commitment. Proceedings of the National Academy of Sciences of the United States of America.

Moore, J.C., Grinsted, A., Zwinger, T. and Jevrejeva, S. (2013). Semiempirical and process-based global sea level projections. Reviews of Geophysics. 51 (3), 484–522. DOI: 10.1002/rog.20015

Neumann, B., Vafeidis, A.T., Zimmermann, J. and Nicholls, R.J. (2015). Future coastal population growth and exposure to sea-level rise and coastal flooding – A global assessment. PLoS ONE 10 (3), e0118571. DOI: 10.1371/journal.pone.0118571

O’Neill, B.C., Kriegler, E, Riahi, K., Ebi, K.L., Hallegatte, S. Carter, T.R., Mathur, R. and van Vuuren, D.P. (2014). A new scenario framework for climate change research: the concept of shared socioeconomic pathways. Climatic Change, 122 (3), 387-400. DOI: 10.1007/s10584-013-0905-2

Peltier, W.R., Argus, D.F. and Drummund, R. (2015). Space geodesy constrains ice age terminal deglaciation: The global ICE-6G_C (VM5a) model. Journal of Geophysical Research – Solid Earth, 120 (1), 450-487. DOI: 10.1002/2014JB011176

Rabus, B., Eineder, M., Roth, A. and Bamler, R. (2003). The shuttle radar topography mission—a new class of digital elevation models acquired by spaceborne radar. ISPRS Journal of Photogrammetry and Remote Sensing, 57 (4), 241-262. DOI: 10.1016/S0924-2716(02)00124-7

Rahmstorf, S. (2007). A semi-empirical approach to projecting future sea-level rise. Science, 215 (5810), 368-370. DOI: 10.1126/science.1135456

United Nations (2014). Adaptation Fund. Accessed August 2015.

177 Responses to “What drives uncertainties in adapting to sea-level rise?”

  1. 1
    Russell says:

    Few factors figure more in the objective formulation , and eventual acceptance , of environmental policy than the candor of the analysts in acknowledging the extent of their ignorance.

  2. 2
    sidd says:

    Thanks for the detail on uncertainties.

    You write:

    “Long-term investment in infrastructure could become a cat-and-mouse game, where monitoring becomes increasingly important leading to reactive adaptation to avoid an unacceptable situation of escalating risk.”

    In my view, long term investment is already a cat-and-mouse game, and i agree entirely that quick, informed and reactive adaptation is absolutely necessary.

    If we look from the beginning of the current deglaciation from 20Kyr to the present as in Blanchon(2009) doi:10.1038/nature07933 Supplementary fig. 3 we see that sea level rise is episodic coming in bursts of an inch plus per year, interspersed by periods of rise of “only” three times smaller, say 10mm/yr. So I imagine that sea level rise in this anthropocene deglaciation will not be a smooth curve either. And I submit that the risk of something like Thwaites letting go and seeing 30mm/yr for a loong time is one that is underestimated. I am sure that someone must have looked at impacts of episodic rise as opposed to steady rise, amd I would like a pointer if anyone has one.

  3. 3
    Dan Miller says:


    Rather than provide detailed comments on your question, let me provide some high-level tidbits:

    1. It may be (and I would say that it is likely) that the “official” estimates we have been given for SLR are conservative and the actual rise will be significantly higher/sooner. See Jim Hansen’s paper on “Scientific reticent and sea level rise”:

    2. Hansen also notes that Greenland is currently losing ice mass at an exponential rate. Exponentials are not your friend and if the rate continues for a few decades, we will have ~3 feet of SLR by 2050 and much, much more than that by the end of the century.

    3. NASA has said that we have passed a tipping point with the West Antarctic Ice Sheet Sheet (WAIS) and its collapse is now “unstoppable”. This adds about 10 feet of SLR to whatever other SLR we get though the timing is uncertain, but seems to be just hundreds, not thousands of years and maybe sooner.

    4. The last time CO2 levels were what they are today (400ppm), sea levels were about 75 feet higher than they are now. This is where we are heading, though it will take some time. Of course, we are continuing to increase CO2 levels.

    5. As you note, once SLR gets underway, we will never have a stable shoreline again until sea level rise a great amount (perhaps as much as 280 feet if we keep burning fossil fuels and/or natural CO2/methane release processes run away). Therefore, retreat is the only long-term adaption strategy for SLR.

    6. Based on what I have read, I would say it is likely we will see 10~15 feet of SLR by next century (and possibly this century – see (1), (2) and (3) above) and this means the bottom third of Florida (and many other places) will not be on the map next century. I think facing this fact may — just may — help us understand the need to get moving to avoid even more serious and unadaptable impacts.

  4. 4
    Edward Greisch says:

    Local officials will continue to complain that climate scientists are not providing definitive answers.
    What people who live near the ocean should do: Move to higher ground.
    What they will do: Nothing.
    What is really going to happen: Civilization is going to collapse about a century before sea level rise has reached a meter.

  5. 5
    Abi says:

    I wish we could have this bit highlighted whenever we discuss adaptation to climate change:

    “It’s important to remember that climate change is not the only issue and multiple uncertainties exist in other fields that can sometimes be greater than the climate signal alone, leading to deep uncertainty.”

    Other problems on the horizon include:

    Loss of biodiversity
    Resource constraints
    Rising population levels
    Water loss etc

    A full systems analysis of this, the ultimate wicked problem, is what we should be doing, instead of focusing solely on climate change.

  6. 6

    Thanks for an interesting and helpful discussion of the difficulties involved where ‘the rubber meets the road’.

    But there is so much emphasis on those uncertainties, and the intractability thereof, that I can’t help but think of Dr. Curry–though to be fair, she seems rather more complacent than frustrated about them.

    So my questions would be:

    Are there success stories, where the efforts mentioned have resulted in useful policy guidance? Are uncertainties narrowing at all? Or are explorations still more often expanding the ‘problem space?’

    In short, is there a discernible ‘delta’, and iF so, what is it?

  7. 7
    Sally Brown says:

    Abi is absolutely right in that there are lots of problems in coasts, and this is just one part of a wicked problem (see NCC article Brown et al. (2014) doi:10.1038/nclimate2344). The big research challenge is to try and link (or untangle) the problems from different disciplines together (or pull apart). Do we need to invest in and educate scientists who can manage coastal issues who have a multi-disciplinary background, more than those who are specialist in one area?

  8. 8
    Sally Brown says:

    Russell – interesting paper. Have you seen: and This really makes you think how the world could change in the next 100 years.

  9. 9
    Sally Brown says:

    We’re really struggled about explaining uncertainty to policy makers in simple language (particularly when we mention the different percentiles of uncertainty is sea-level rise). Some nice papers are: DOI: 10.1002/wcc.253 and doi:10.1038/nclimate2505. At the end of the day, it depends of users’ needs and the level of acceptable risk they are willing to take when building on the coast (e.g. building a nuclear power plant v. a community centre). I guess as scientists it is up to us to explore the uncertainty space, and this is something that we are still trying to do at different spatial and temporal scales. As impact scientists, we tend to lag behind physical scientists in our understanding of this (as we are the next step along in the scientific process of drivers – impacts – adaptation): It’s not complacency, more trying to understand exactly what the uncertainties are, how big they could be, and then understanding their interactions.

  10. 10
    Hank Roberts says:

    So shallow salt water is very productive habitat biologically.

    All we need to do is remove all the crap concrete asphalt oil paint heavy metals etc. covering coastal Texas, North Carolina and Bangladesh, and be ready to seed the areas with oyster shell and eelgrass for fish spawning areas, right?

    Oh, yeah, high-rise cities along the northern border too, for the displaced people.

  11. 11
    Geoff Beacon says:

    Sally Brown’s article has

    what are we adapting to, and when could this occur? Is it about 1m of rise by 2100? Or 1.4m?

    Dan Miller #3 said

    4. The last time CO2 levels were what they are today (400ppm), sea levels were about 75 feet higher than they are now. This is where we are heading, though it will take some time. Of course, we are continuing to increase CO2 levels.

    I will be revisiting these comments to see if the discussion here can give me a few key points when bothering policy makers- a few key points without me doing a PhD first.

    In the blue corner we have a minimum of 1.0m by 2100. In the red corner something much larger – probably a bit less than 25m – with more as time goes by.

  12. 12

    thanks RC and Dan Miller #3

    We might want to ponder how sea level rise itself will trigger and amplify exponential warming. (Heat, melt, repeat) Two or 3 feet by 2050 means considerable flooding of the fairly extensive permafrost zones surrounding the Arctic Ocean. I see that permafrost holds 3 times the carbon that is in our atmosphere now – a nice new video overviews the science:

    One can only imagine the extent and efficiency of ocean flood waters melting permafrost. With open waters, storm surges should be a factor in the extent of flooding. We have to guesstimate because it’s so difficult to find a map plotting of a sea level change area – such as the interactive map on geology map or Google Earth map for the Arctic region. (why do the altitude maps stop at the polar circles? How difficult is it to measure polar region land altitudes? Why is that kind of interactive map missing from general circulation? Is that something any data enthusiast could accomplish?)

    I read here that more carbon released from permafrost – especially as methane, causes faster heating of the Northern Hemisphere. Heat drives faster melts, deluge rains instead of snow, and more feedback.

    Also with significant sea level rise – say 2 or 3 feet, Antarctic ocean rise will lift up the ice sheet boundary where it meets the ice caps. And sea level rise will affect the glaciers that have grounding lines upstream and under the ice – the grounding line moves further upstream… would this touch some of the deeper lakes under the ice cap? As higher sea levels lifting the glacier, then the tides would constantly flex the ice tongues breaking and releasing the ice opening up the ice flow “cork in the bottle”. More exponential destabilization.

    Reading about all this here in RC articles and comments, really, now all we are discussing is the timeline for these events. I wish there were more scenarios posted on this — but from the confluence of these factors, it seems plausible that the the 2030’s – twenty years hence – will be quite dynamic – and beyond (the 2050’s??) could be the decades of cryo+carbon cataclysms.

    Perhaps RC could post an annual prognostication scenario discussion – say maybe every June 21 solstice seems apropos. Everything is changing so fast, time for setting down predictions.

  13. 13
    Andy says:

    I’m sometimes disheartened when I hear that planning for sea levels expected beyond 2100 probably isn’t relevant; not that the author makes this mistake. I’m mean really, how old is Westminster Abbey and what’s its elevation? The idea that somehow humanity will be free of geography in 100 years is ludicrous in my opinion.

    At any rate, as a biologist who sometimes helps set up nature conservation areas, often near sea level, I’m fully aware that there isn’t going to be any open land left in the near future. What we’re setting aside today for nature is essentially in perpetuity and all we’ll ever be able to do.

    Add on the uncertainties associated with shoreline retreat along a coastline dominated by barrier islands and a 1,500 to 15,000 to 1 slope and things get really dicey. The simple maps that project inundated areas given a certain amount of sea level rise are not entirely worthless for the prediction of real consequences on such a coast, but I look forward to reading Dr. Brown’s publication which sounds like it might take a much more comprehensive approach.

    Unfortunately, many of my colleagues have taken on a philosophy that future sea level rise is too scary and complicated to contemplate beyond 2100 and so have stuck their head in a sack.

    It would be very helpful to see more projections that go out to 1,000 years or even more. And if some engineers think humanity will find a way out of the sometimes projected sea level rises of 70 feet in a couple thousand years, then I’d like some idea of what shape these miracles of science will take.

  14. 14
    Titus says:

    There have been no cases of any unprecedented sea level rise here in New Zealand. The rise is at the historic average with some places showing a decline.
    Check out –

    We, at least, can sleep easy.

  15. 15
    Rolan O. Clark says:

    If the diameter of the earth is 80000 miles what are the factors of the earth’s rotation speed, weight of water, mantle shifting (earthquakes) and other factors that may modify how much earth protrudes from the water, known as sea level?

  16. 16
    Chris Pratt says:

    From reading the first few paragraphs of this, I was inclined to conclude that an accelerating sea level rise from the previous century could be gradual enough to allow for a natural adaptation to occur. In contrast to other articles I have read, SLR in comes across as no more alarming then the myriad of other uncertainties that exist in the future that may or may not become a major problem that may or may not requires immediate action or public policy changes.
    A climate denier may look at this and say here is a scientist who saying that we may be looking at SLR of between .025-.25 meters in the next century. These seemingly small numbers albeit completely made up, fit the criteria for the only certainty we have, an accelerating SLR over the next century.

  17. 17
    Andy Revkin says:

    Excellent piece and the conundrum is even worse because the politics of dealing with sea-level rise — whatever the rate — is awful. Mayor Bloomberg, strongly pushing for action on climate change, couldn’t incorporate the sea-rise reality in his final big climate speech before leaving office, proclaimed the city would not retreat.

    This piece explores that end of the issue: Can Cities Adjust to a Retreating Coastline? via @dotearth

  18. 18
    Randall W. Parkinson says:

    Actually, the past is the key to the future.

    And based upon late Quaternary stratigraphic data from peninsular Florida’s shelf and coastal zone, historic wetland accumulation rates, and residence time of coastal construction projects (i.e. beach ‘nourishment’, dune ‘restoration’), by mid-century the rate of predicted sea level rise will result in erosional shoreface retreat and ultimately overstep of both the natural and built environment.

    The ‘Business as Usual’ strategies of protect and defend and even accommodation will provide temporary relief (say perhaps another decade or two), but ultimately the only effective adaptation action to ensure resilience of either environment is managed (aka strategic) withdrawal (aka retreat).

    This will require an approach to coastal zone management that is 180 degrees from what we have done for the past 150+ years. Thankfully, despite the politics of climate change, a few regions in Florida (i.e., SE FL Climate Compact, Satellite Beach) are beginning to consider and plan for the future in a realistic way. The larger question is…how long will it take for others to follow and will it be too late by then to successfully adapt with minimal calamity?

  19. 19
    Chris Brown says:

    Can we learn from the stromatolites, or are we just another passing phase in the planets history, and possibly the quickest? What is the asymptote of change, not only sea level but atmospheric composition? How much pollution and leaching wiill occur from all our coastal dumps? Here I am in Kiribati looking to help with adaptation and I meet a sailor who has just come 5000miles from Panama single handed. He says he sailed 1000 miles before he was clear of the trash.

    Nearly every civilisation before us has died of it’s own ordure [Wilf Radcliffe, Epsom 1958]. Our ordure is not only CO2 and othe,new, gases, but trash, polluted groundwater and salt in the fields. What a legacy. And Kiribati has joined that consumer society – at least in South Tarawa it has.

  20. 20
    Richard Caldwell says:

    Edward Greisch: Civilization is going to collapse about a century before sea level rise has reached a meter.

    Richard: So you’re on the “side” which says that sea level rise will be ever so slow, eh? Myself, I’m thinking that one meter will happen by 2080 or so. (though with extremely large error bars)

  21. 21
    Robin Johnson says:

    Barring a sainthood’s worth of major miracles, I don’t see how we avoid several meters (5 to 10+) of sea level rise by 2200. That seems clear given the science and evidence. How much before 2100 is less clear although I’m willing to bet on Hansen rather than the optimists – and so I think we’re getting 2-4m instead of just 1-2m.

    Admittedly, entire cities can be built almost from scratch in 10 to 30 years [see China and the US South]. Entire cities can be rebuilt from rubble in just 10 to 20 years, see post-war Europe and Japan. Ironically, if the sea level rose by several meters in a decade, the suffering would be epic – but the recovery would be relatively quick as the ports were rebuilt and coastal communities reshaped. Many cities would simply vanish and new ones would appear. But it would be like recovering from a world war or the like.

    But this is a slow motion catastrophe. We know that New Orleans, Venice, Miami, Mumbai and many other cities and regions will have to be abandoned sooner or later. It is impossible to save them from 5 or 10 meters of sea level rise. Other cities would require epic dikes and storm defenses to remain viable. Should we plan a fighting withdrawal from Norfolk? Baltimore? Houston? Mobile? Tampa?

    What about New York? It is going to need some mighty defenses.

    Do we even spend a dime on New Orleans? Or Venice? Do we start moving what we can out now?

    We need to design our dikes so that they can be raised as we need them. And in the US and East Asia – they have got to be able to withstand 5+ meter storm surges as the major cyclones plow into the dikes. Port facilities will benefit from being “floating” cities that can be inched up as the waters rise.

    Of course, some areas will collapse creating war and refugees. And suffering.

    Sad to say, we have let our children and grandchildren down so far. I apologize on behalf of those who were ignorant and foolish and those of us who understand but couldn’t convince the others soon enough.

  22. 22
  23. 23
    Omega Centauri says:

    Richard Pauli@12. SLR from ice melt is unlike SLR from the thermal expansion of seawater. Because the bulk of the icemelt is localized to a few areas, Greenland, West Antarctica probably, we need to treat the effect of the gravitational attraction of (land) ice for water. It turns out that within about two thousand miles of the site of iceloss, the effect on sealevel is negative. Maximum rise is counterintuitively on the other side of the planet. So near GIS and WAIS sea levels might actually drop rather than rise. At least this one driver of ice sheet instability isn’t operative.

  24. 24
    wili says:

    Good points, Robin. But all of these major construction projects (and some that have been considered would be the largest projects undertaken by humans) will take enormous amounts of materials and energy and concrete, all of which will have to be carbon neutral. But there will lots of other projects demanding those very limited resources.

  25. 25
    Sally Brown says:

    Andy, I once heard that Westminster Abbey (or a predecessor) was built on a muddy island / mudflat on the Thames, as that was the place of highest elevation (and therefore closest to God). The streets around it were river channels. During the summer 2007 English flooding (albeit it inland) many towns were flooded, including Tewkesbury in Gloucestershire. However, in Tewkesbury the Church was not flooded. They really knew what they were doing!

    For long term sea-level rise projections, see: (Table 13.8)

  26. 26
    Sally Brown says:

    Andy – good statement about how to deal with the politics of sea-level rise! Robin Johnson also makes a good point about how fast cities grow. I was in the Maldives last year – to lowest lying country on Earth – which is largely dependent on tourism for its income and development. We heard that the tourist operators were less concerned regarding long-term flooding than short-term erosion as infrastructure has a limited lifetime due to the standard of which tourists expect (say 20 years). With flooding they can simply build upwards at the next infrastructure renewal. With cities, could we do the same? Do will have the political will to admit defeat to sea-level rise and build a new city, or are we too attached to our present surrounds, history and culture? Maybe we need floating cities…..?

  27. 27

    Roland at 15,

    Earth’s diameter is closer to 8,000 miles.

  28. 28
    Titus says:

    I mentioned New Zealand earlier. I know our land development consultants and engineers take all the available scientific knowledge and actual data into account.
    The problem we have to deal with is local authorities trying to find ways to get needed projects funded by central government and the like. Or cover up past failure. The whole exercise gets politicized using scary unfounded hypothesis usually associated with current global climate change propaganda.
    All falls on our taxes and Joe public is on to this of course, but very hard for us to get a voice. Often I hear folks who raise questions put down as “deniers” a word I often see used here.
    As Joe public will ultimately foot the bill I always call for a more open and transparent discussion and stop this “denier” name calling and break through the alarmism and politics.

  29. 29
    Eli Rabett says:

    It’s not the average sea level rise it’s the combination of average sea level rise, king tides and storm surge. If NYC loses the road and rr tunnels, etc

  30. 30
    Robin Johnson says:

    @Wili – I’m hoping we’re carbon neutral sooner rather than later. If we don’t ratchet down the CO2 – the climate crisis will be dire for our descendants. A 4 to 6C rise would be a PETM-like event – a real horrorshow.

    Even if we do the right thing and get the carbon under control in time to avoid a PETM (I’m actually optimistic we will…), we are going to have to adapt to the damage already done and in progress which is going to be a lot of GIS and WAIS melting. The collision between climate change and excessive population growth is going to generate a series of refugee crises not seen since like ever.

    A significant fraction of the global economy and hence population is dependent on the coastal regions and the ocean. We are going to need to adapt our ports and coastal cities to the continually rising seas. Hence my questions – do we defend Norfolk VA? Can we successfully defend New York? Ironically, Europe has a lot of rocky coastline and sufficient elevation – adaptation will be relatively painless by comparison – except the Netherlands. Boston MA, rocky, no big deal. Tampa FL? Big problem. New Orleans? Doomed. Estuaries will be adversely affected – no doubt.

    As Sally Brown makes clear in the article though, seawater infiltration, subsidence and a bunch of gritty geologic details associated with sea level rise are going to make civil engineering a nightmare. Plus, we have to deal with potential changes in rainfall (lower and higher) that’ll make things harder to figure out. The Climate Scientists know rainfall is going to change and can even make some decent guesses on those changes – but they are far from certain as yet.

    But we can’t just throw up our hands and hope for miracles or pretend its not happening. We owe it to our descendants to start planning now.

  31. 31
    Ray Ladbury says:

    We’ll be happy to stop calling you a denier as soon as you stop denying the science.

  32. 32
    Hank Roberts says:

    ‘Titus’ doesn’t bother to deny the science.
    He ignores the science.

  33. 33
    Titus says:

    Ray Ladbury:
    Land development engineers do not deny the science. Construction requires long term risk assessment and planning. The companies they work for depend on their future reputation.
    Questioning the wild claims of sea level rise when our local topographical studies say otherwise is at least worthy of discussion.
    Your reply indicates to me that you could be part of the problem.

  34. 34

    #9, Sally Brown–

    Dr. Brown, thanks for your response. Look forward to having a look at those cites!

  35. 35
    Edward Greisch says:

    20 Richard Caldwell: I mean that civilization will collapse “ever so soon.” Sea level rise need not be slow. I read somewhere recently that some people in Florida now wade across their front yards at high tide, but they still say sea level is not rising. Civilization has already collapsed in Syria, South Sudan, Libya, Somalia, …. So if 1 meter of sea level rise happens by 2080, it is more than half a century after civilizations started collapsing. Collapse is spread out in time. When do you call it?

    The problems are: Local officials have not studied statistics while the scientists have not been local officials.
    Local politicians cannot accept that their town will no longer exist.

  36. 36
    Edward Greisch says:

    “Native American Tribe Gets Federal Funds to Flee Rising Seas”

    It turns out the government is offering $2 million per trailer-on-stilts and is trying to keep this “tribe” together as a unit. The comments have disappeared. The comments were very negative. A linked map showed many hamlets and towns in similar shape in Louisiana. New Orleans is there and should be moved, but New Orleans is not included. I don’t see the same linked map now.

    “The funding stems from Louisiana being named one of 13 winners in HUD’s National Disaster Resilience Competition.” Because the government can’t spend that much for so little very many times. Some of the remaining 100 people still do not want to leave, even given such a generous offer.

    The lesson for end users: Give up. People will move soon after rising sea level kills them.
    The lesson for scientists: Forget about them. People will move soon after rising sea level kills them.

    Sally Brown, are you frustrated enough yet?

  37. 37
    Edward Greisch says:

    See: “Ice Melt, Sea Level Rise and Superstorms: The Threat of Irreparable Harm” by James Hansen et al

    They are talking about much faster sea level rise. “Consequences include sea level rise of several meters, which we estimate would occur this century or at latest next century, “

  38. 38
    Dan Miller says:

    James Hansen in a video discussing his paper “Ice Melt, Sea Level Rise and Superstorms: The Threat of Irreparable Harm”:

  39. 39
    Ann F. Kah says:

    We have too much of the “I’m going to be OK, so why worry” attitude in the developed countries. We are neglecting the global effects of, say, unpredictable weather patterns causing crop failure and famine, and coastal displaced people who must flee inland to already-overcrowded countries. The inevitable effect, and our greatest danger, is the war that results. That will affect most of us long before the ocean laps at our doorsteps. We can’t afford to neglect the effects just because they’re on the other side of the globe.

  40. 40
    Mal Adapted says:


    The problem we have to deal with is local authorities trying to find ways to get needed projects funded by central government and the like. Or cover up past failure. The whole exercise gets politicized using scary unfounded hypothesis usually associated with current global climate change propaganda.All falls on our taxes and Joe public is on to this of course, but very hard for us to get a voice. Often I hear folks who raise questions put down as “deniers” a word I often see used here.

    Titus, there is a lopsided consensus of working climate scientists that the Earth’s climate is warming and that humans are largely or entirely responsible. In the context of anthropogenic global warming, a denier is someone who dismisses the scientific consensus. If your information about AGW comes from politicians, TV news presenters and politically-motivated bloggers, you are much more likely to deny AGW than if you get your information from primary scientific sources. is a blog for working climate scientists, and interested non-scientists who prefer to get their information from “the horse’s mouth”. For newcomers, the “Start Here” tab at the top of the page and links on the right-hand side under “Science Links” are excellent places to start.

    One thing you should know is that arguments from consequences are not valid in scientific debate. When climate scientists discuss the evidence with each other, the questions that matter to them are “Does the evidence show that the Earth’s climate is warming, or not?” and “Does the evidence show that burning fossil carbon for energy causes warming, or not?” They do not ask “will my taxes go up if I accept these findings?” If you don’t want to be called a denier on RealClimate, don’t make arguments from consequences.

  41. 41
    Jim Eager says:

    Robin (@21), China built its ‘instant’ fiat cities during an unprecedented era of rapid economic growth. Europe was rebuilt thanks to the Marshall Plan, which was funded by the US during its own postwar economic boom. Both contributed greatly to the rapid rise of CO2 in the second half of the 20th century and early 21st. Building sea walls and moving ports and cities on a global scale will do the same this century, even as the sea literally swallows trillions of dollars of investment in existing infrastructure.

  42. 42
    nigelj says:

    Titus, I’m also from NZ. I dispute your comments.

    We have had sea level rise above historical norms. In other words sea level rise since 1900 has been greater than previous centuries and is similar to other countries, as below.

    However the general sea level rise trend has a lot of local variation. The reasons are there is quite a lot of geological uplift in NZ, leading to less sea level rise in some places. There are other regional factors.

    However there remains a generally rising trend, and this is likely to accelerate about the middle of this century according to the IPCC. So don’t be so complacent.

  43. 43
    Edward Greisch says:

    “This uncertainty is illustrated by Pollard et al. (2015), who found that addition of hydro-fracturing and cliff failure into their ice sheet model increased simulated sea level rise from 2 m to 17 m, in response to only 2°C ocean warming and accelerated the time for substantial change from several centuries to several decades.”

    Yikes! Tell me it isn’t so.

  44. 44
    Paul Segal says:

    Robin, if this research is correct then the PETM is not a completely valid comparison. Nature Geoscience (2016) doi:10.1038/ngeo2681 It seems the issue is whether or not there is a lag between increase in CO2 levels and temperature increase. Relatively speaking they report the PETM did not have lag. CO2 was released at a somewhat slower rate during the PETM.

  45. 45
    Jim Steele says:

    @Ray Ladbury.

    I am not sure who is denying the science, you are Titus?

    I followed Titus’s sea level links for New Zealand and sea level rise is certainly not accelerating there. How is that science denial???

  46. 46
    Don Barber says:

    Titus from NZ states: “There have been no cases of any unprecedented sea level rise here in New Zealand. The rise is at the historic average with some places showing a decline.” Titus cites four 20th century tide gauge records for which NOAA has calculated long-term SLR rates ranging from 1.3-2.4 mm/year.

    As is often the case, understanding the implication of the tide-gauge data requires longer-term context.

    Fortunately, in a 2008 GRL paper, Roland Gehrels and colleagues published some of the key information for coastal New Zealand. At their southeastern NZ study site:

    “Sea level was rising slowly (0.3 ± 0.3 mm/yr) from AD 1500 to AD 1900, but during the 20th century the rate increased to 2.8 ± 0.5 mm/yr, in agreement with instrumental measurements commencing in 1924.” [and in agreement with the tide gauge rates referenced by Titus.

    Gehrels and others (2008) comment that this is “a significantly higher rate of sea-level rise during the 20th century as compared with preceding centuries.”

    Gehrels, W. R., B. W. Hayward, R. M. Newnham, and K. E. Southall (2008), A 20th century acceleration of sea-level rise in New Zealand, Geophys. Res. Lett., 35, L02717.

  47. 47
    Titus says:

    Hank @32 says:
    ‘Titus’ doesn’t bother to deny the science.
    He ignores the science.

    Really Hank? I’m familiar with the document and question whether you have actual read it.

    Here’s a quote from the conclusion:
    “Firstly, it continues to indicate that in New Zealand, at least, there has been neither a significant change in the rate of sea level rise nor any detectable acceleration.”

    Appears to me from your comment that you to could also part of the problem.

  48. 48
    Titus says:

    Nigelj @42 says:

    “Titus, I’m also from NZ. I dispute your comments.”

    See my reply to Hank Roberts. From the comments section of the paper he highlighted:
    “Firstly, it continues to indicate that in New Zealand, at least, there has been neither a significant change in the rate of sea level rise nor any detectable acceleration.”
    Hmm. Looks like we have a genuine “scientific” discussion. Now please don’t call me a denier.

  49. 49
    Titus says:

    Mal Adapted @40
    When alarmist language is used about our sea levels and local topographic data says otherwise and anybody who disputes it is called a denier then something has gone terribly wrong.
    What’s that got to do with “arguments from consequences”?

  50. 50
    Ray Ladbury says:

    Jim Steele,
    Titus has a long record of denying the science of climate change–as do you. It is disingenuous to look at a small, isolated area when the question concerns global trends. If you want to look at localities, look at what the science predicts for those localities.

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