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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. 151
    Richard Caldwell says:

    Thomas: What are the fundamental drivers of the Arctic Decadal Oscillation? Are they changing or a constant you think?

    Richard: Yeah, I’m of the opinion that there aren’t any natural cycles anymore, but only unnatural cycles driven by the new normal. Whatever the AMO was, it ain’t that anymore. PDO? Ditto. One glaring example is El Nino. Scientists are pondering that the relative frequency of ENSO states is drifting because of climate change. So, while trying to attribute stuff to that which doesn’t exist in its old form is useful, attributing stuff to the dead-and-gone-old-form is an error.

  2. 152
    Hank Roberts says:

    PPS: Jim Steele has been posting “it’s natural variation” here since 2004.
    Use the search, folks, if you’re wondering.

  3. 153
    Hank Roberts says:

    Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse
    16 March 2016
    Accepted Online: 28 JAN 2016
    Johannes Sutter, Paul Gierz, Klaus Grosfeld, Malte Thoma and Gerrit Lohmann
    Published Online : 29 MAR 2016 07:40PM EST,
    DOI : 10.1002/2016GL067818

  4. 154
  5. 155
    alan2102 says:

    China tosses in a wildcard…
    March 31, 2016
    China proposes $50+ trillion Global UHV grid connecting all power generation including massive wind farm at the North Pole by 2050
    China is proposing a $50+ trillion global energy grid. Global Energy Interconnection (GEI), a vision of a world power grid, was outlined by the State Grid Corporation of China (“State Grid”)
    It would be based upon a global network of Ultra High Voltage power lines connecting global power generation including massive wind farm at the North Pole and solar power from equatorial areas to energy users around the world.
    If renewable generation grows at an annual growth rate of 12.4 percent over the world, then by 2050 renewable energy shall increase to 80 percent of total consumption, realizing clean energy supplement forever and completely solving the dilemmas caused by fossil fuels.
    By 2050, the total CO2 emission will be controlled at about 11.5 billion tons, half of emissions in 1990, holding the temperature rise to within 2 degrees.
    The accumulated investment on the global grid will exceed $50 trillion, tremendously boosting the development of new-emerging strategic industries, renewable energy, new materials and electric vehicle.
    end quote


    NB: the Chinese are big-time long-term PLANNERS, with a history of carrying out their objectives, e.g. the long series of largely-successful 5-year plans. This particular project is enormous, well beyond the usual bigness of their vision, (therefore more than the usual likelihood of failure), but I would hesitate to bet against them.

    More details, google: China Global “UHV grid”

  6. 156
    Edward Greisch says:

    153 Hank Roberts: Do you have a URL for that?

  7. 157
    Lawrence N. Allen says:

    PhD researchers need about three projects per year just to survive. That is why “more studies are needed” is the most universal scientific conclusion. When considering drivers of uncertainty, professional considerations must be taken into account.

  8. 158
    Hank Roberts says:

    for EG:

    DOI : 10.1002/2016GL067818

    Copy that entire line
    (starting with D and ending with 8)
    Paste it into the search box for any web browser.

    “A DOI or Digital Object Identifier … identifies digital content …. It is unique to each piece of digital content and provides a persistent link to that content no matter where it is located on the Internet.”

  9. 159
    Hank Roberts says:

    > Lawrence N. Allen … why “more studies are needed ….”

    Science is inconvenient and annoying.
    It’s only been a feature of life for a couple of centuries
    Humanity did fine without science for, oh, ten thousand years or more.

    Then all of a sudden there’s all this change. Disconcerting, eh?

    People proclaim two contradictory things:

    (1) more studies are NOT needed, and
    (2) the science is NOT settled.

    The way to rationalize believing both is: science is NOT wanted.

  10. 160

    #155–OK, I love me some wind power, but really? A wind farm at the North Pole?

    The first question is, is there seasonal sea ice still at the Pole in 2050? If there is, then we have this little problem called “transport drift,” in which billions of tons of sea ice ‘try’ to flush those turbines into the North Atlantic via the Fram Straight. Better hope the tensile strength of that UHV cable rivals that needed to suspend the hypothetical ‘space lift’.

    If not, then there are two issues. One is stationing turbines in 4,000+ meters of water. OK, floating platforms are the next thing in offshore wind, but that’s one hell of an anchor cable–or are we to imagine a free-floating rig with some kind of station-keeping capability? What does that cost in fuel/energy?

    Then there’s getting the power to users. I know that submarine data cable has become highly reliable, but intuitively at least, UHV carrying some pretty unholy amounts of power might not be quite so amenable. Ultra-high tension terawatts and very high-pressure salt water–what could possibly go wrong?

    That’s just for starters. But really, wouldn’t it be a whole lot easier, cheaper and safer to put the thing on Ellesmere Island instead? A quick search suggested that wind speeds aren’t that different.

    One hopes the rest of the concept is a bit better thought out–or at least that’s my initial reaction. Maybe I’m being guilty of vicarious NIMBYISM on Sanata’s behalf here, but sheesh!

  11. 161
    Edward Greisch says:

    158 Hank Roberts: Thanks. Got it. So they made a model that is sort of like a GCM.

  12. 162
    Ray Ladbury says:

    Lawrence Allen: “PhD researchers need about three projects per year just to survive. That is why “more studies are needed” is the most universal scientific conclusion.”

    Utter complete horsecrap. Did you ever even take a science class? More studies are always needed. Every study raises new questions. Do yourself a favor and don’t pontificate on subjects where you are ignorant.

  13. 163
    Hank Roberts says:

    Yusuke Yokoyama et al. Widespread collapse of the Ross Ice Shelf during the late Holocene, Proceedings of the National Academy of Sciences (2016).

    DOI: 10.1073/pnas.1516908113

  14. 164

    My last–“trans*polar* drift, of course. Damn spellchecker anyway.

  15. 165
    alan2102 says:

    Kevin #160:

    I don’t have specific answers to your questions. The best resource for those answers (or info on work toward answers) might be Zhenya Liu’s book, published last year:
    Global Energy Interconnection, 1st Edition,
    Author: Zhenya Liu
    Imprint: Academic Press
    eBook ISBN : 9780128044063
    Print Book ISBN : 9780128044056
    Pages: 396
    Proposes a broad concept: global energy interconnection, filling the gap between, discrete technology development and global interconnection, proposing the interdependency of energy systems [end quote]

    Keep in mind also that the arctic stations and connections are in “phase 3” of the plan — in the 2030-2050 area. In other words, quite a bit of time for the engineering. “Phase 1”, domestic phase, is underway already. See links below for details.


    more background, fwiw (these are not in reply to Kevin’s specific questions):
    China Rolls Out Proposal for Worldwide Grid
    China is building 7 ultra high voltage (UHV) projects
    A $100 Trillion Global Energy Internet by 2050?
    January 18, 2016
    It’s about Time to Construct Global “Electricity High-speed Network”
    Released on: 2015-10-13

  16. 166
    Toni Massari says:

    I am no climate scientist, though I read Environmental Management, and my question is this:

    We warn about the PHYSICAL impacts of Sea Level Rise, but I don’t see any info or concern about the early effects of inundations into the lowlands, where these include Contaminated Land, Landfills, Cemeteries, Toxic/Radioactive waste, Repositories, Ammunition dumps, Underground fuel stores, Plague/ Ebola / Foot & Mouth / Anthrax pits or those harbouring other virulent pathogens with pandemic potential.

    SLR will begin from below, not like a tsunami or a standard flood caused by meteorological conditions.
    It will begin by infiltrating soils, porous rocks and sits, inundate lava tubes, animal warrens etc…
    It will saturate contaminated land, dissolving toxics and pathogens.
    It will be global and so simultaneous

    This means that we will see chemical, biochemical, pathogenic, mutagenic and teratogenic impacts long before the physical impacts even appear.

    FIRST though, the oceans have to fill every underground cave and tube, saturate all props rocks and soils, so the increase in freshwater contribution to the Oceans will not be immediately obvious… but the moment these processes are complete, SLR will be sudden and catastrophic.

    Longshore drift and ocean currents would distribute the leachates first along the coasts and then gradually out to sea.

    … but I may be wrong of course.

    I hope so!

  17. 167
    patrick says:

    #166 Tony Massari:

    If I understand your first thoughts correctly, I think about this often when there’s flooding. Floods used to be mainly water disasters but now they’re becoming toxicity emergencies too. I hear the same thing, first-person, from people affected, in news reports. For instance, I heard it from someone innundated in the historic Houston floods from rains that peaked Monday.

    On background, meteorologist Eric Holthaus references the warming climate:

  18. 168
    Hank Roberts says:

    > early effects of inundations into … Contaminated Land

    Really, really important.

    The new intertidal and shallow water — formerly coastline property — is (in the US, at least) going to become public land (as defined by the high tide line). Are we going to wait until that happens and have the public do the cleanup?

    Or is there an economic motive for coastal property owners to do the cleanup because the new shallow/tidal water will be a food source and nursery for fisheries, toxic or not — so we could make it a safe clean part of the ocean.

    Who’s working on this? Coastal management people?
    Oyster farm mega-magnates?

  19. 169
    Hank Roberts says:

    Well, a sad reminder that most of the people on the planet are still grinding away at life (from today’s NPR interview with people from the Cornell Ornithology lab):

    — in Asia coastlines are being built out with seawalls and fill. Sixty percent of the total intertidal already buried. Devastating to migratory birds and many other species.

    Plenty published, though we in the West rarely hear it.
    Just one bit, you know how to find more:

    Impacts of tidal land reclamation in Bohai Bay, China: ongoing losses of critical Yellow Sea waterbird staging and wintering sites

    This is exactly the kind of area we — humanity — should be pulling back from and cleaning up to increase the available intertidal as sea level rises.

    Life on Earth: we’re doing it wrong.

  20. 170
    Nemesis says:

    @Hank Roberts, #169

    Did you know, that Doctor Faustus was a dike warden? Anyway, I am more into Mephistopheles.

  21. 171
    Hank Roberts says:

    “… The EU’s Sentinel satellite system has begun monitoring six mighty polar glaciers in near real-time….
    … “The next step is to expand the service. Future sea-level projections really only allow for imbalance in places we know about today. There are ice streams that may not have activated yet, and that’s why we’d like to routinely monitor perhaps 20 to 30 other sectors of Antarctica and Greenland.

    “That’s our intention, together with Esa as part of their climate change initiative.”

    An Austrian team is developing a similar service, and here at the European Geosciences Union General Assembly this group, known as ENVEO, showcased some of its own ice velocity maps. It has some very impressive static (averaged over time) renderings of Antarctica and Greenland.

  22. 172

    “Life On Earth–We’re Doing It Wrong”

    Deserves to be a shirt/mug/bumper sticker, even if that would be an irony of its own.

  23. 173
    Richard Caldwell says:

    Hank: formerly coastline property

    Richard: Great point. One problem is that the coastline doesn’t go quietly or on a schedule. A hurricane here, a superstorm there…

    So we’re faced with things like Fishbowl New Orleans with, best case, all the former residents flopping about the perimeter.


    Hank: Sixty percent of the total intertidal already buried.

    Richard: Sigmoid? Hopefully that represents nearly all of the built-up areas so it will level off. (pure speculation)
    Of course, all those other intertidals will have to move upwards. Hope the slope doesn’t change…

  24. 174
  25. 175
    Hank Roberts says:

    P.S., details on the data problems with sea ice satellites at

    So, to our stories of woe. All of these instruments are designed for 5 years’ operation. F-15 giving (mostly) good data after 17 years is spectacular for this type of satellite. Notice that most of these potential data sources are already past their design life. Since February 2016:

    F-16: the sounding channels quit working early February
    F-17: April 5th data quality impaired on one of the surface imaging channels, data volumes sent are greatly reduced.
    F-18: Mostly ok, but reduced volume of data. Many orbits’ data not making it through.
    F-19: Data ceased flowing February 2
    AMSR2: Data outage afternoon of April 15th through morning of April 16th.

    F-15, the oldest of the crowd, is still sending basically normal data volumes at basically normal volumes.

    So, hiccups all around the sea ice analysis world. The NSIDC was using only the F-17 SSMI-S, so has to rebuild their system to work with another instrument. The AMSR2 temporary outage affected some centers seriously as they relied only on that instrument. The US NWS uses both F-15 and F-17, and so far seems to be ok. I haven’t checked the operating status of the OSI-SAF sea ice (European analysis). If I remember correctly, they also use more than one instrument, so should also be ok.

    More gory details below the fold …

  26. 176
    Brendan P Dulohery says:

    Thanks for this article. In my climate change course we have often discussed the lack of planning and especially implementation in coastal cities in terms of preparation for sea level rise. It seems like most presidential candidates this cycle refuse to adopt any policies that reflect awareness of climate change, let alone catastrophic sea level rise in less than 100 years. As we have seen in Flint, it seems like many people will start having to be seriously harmed by sea levels rising in coastal cities (e.g. major power plants in California being submerged) in order for change to be implemented.

  27. 177
    Cody Nichols says:

    You are spot on! It’s extraordinarily difficult to make plans for the future with so much speculation as to what the future may hold. I guess, I have to ask, why can’t we just build up hard barriers in anticipation of the coming change with the intention of them lasting for the next 100 years? I understand that from a financial perspective it might be overkill. But, if the change is coming, even if we don’t know exactly what to expect, it would seem to me that planning for the worst would cover all of the potential outcomes. Would it not?