New survey on likely slr: up to 3m by 2300 with unmittigated emissions

[wili]

http://www.realclimate.org/index.php/archives/2013/11/sea-level-rise-what-the-experts-expect/comment-page-1/#comment-428150

This is from the RC coverage of the study:

Sea-level rise: What the experts expect

In the long run, sea-level rise will be one of the most serious consequences of global warming. But how fast will sea levels rise? Model simulations are still associated with considerable uncertainty – too complex and varied are the processes that contribute to the increase. A just-published survey of 90 sea-level experts from 18 countries now reveals what amount of sea-level rise the wider expert community expects. With successful, strong mitigation measures, the experts expect a likely rise of 40-60 cm in this century and 60-100 cm by the year 2300. With unmitigated warming, however, the likely range is 70-120 cm by 2100 and two to three meters by the year 2300.

Here's the link to "highlights" from the original--abstract, graphs, and comments on graphs:

http://www.sciencedirect.com/science/article/pii/S0277379113004381

To see what a 3 m rise would mean to various locations, here's a rough, interactive tool (but please post links to any sites that do this better):

http://flood.firetree.net/

To me, the survey misses the point Richard Alley and others have been trying to make wrt slr. Even if it is a remote possibility, it is important to know what the physically possible highest-end possibilities are, just as you wear a seat belt even though chance of being in a crash in any particular car trip are generally rather tiny.

Here’s the relevant Alley lecture, afaics, “Slip Slidin’ Away”:

[Lennart van der Linde]

Hi wili,

Interesting survey: figure 3 in Stefan's post shows 14 (?) out of 90 respondents think there's a 17% chance that 175 cm or more by 2100 is possible, and 4 of them even think there's a 17% chance that 325 cm or more is possible, even if Stefan himself thinks this 17% chance starts at 125 cm at the most and more than 175 cm is implausible. Makes me wonder who those 14 outliers are.

[wili]

"Makes me wonder who those 14 outliers are."

Good question. It gets at another problem with these polls. I would consider the top publishers on the subject as having greater weight than someone relatively new to the field, or someone who has published a lot of stuff that has later been shown to be not well thought out. But that kind of weighting can't come in to such a poll.

[AbruptSLR]

wili/Lennart,

It would be a great thing if society adopted the Precautionary Principle and reduced GHG emissions sufficiently to avoid the SLR risks expressed by the 4 experts expressing their belief of a 17% chance that following RCP 8.5 could result in SLR of over 3.25m by the end of this century.  Nevertheless, I would like to note that unlike global warming, which cannot necessarily be avoided by acting locally; the risk of inundation associated with ASLR can effectively be mitigated by acting locally, as indicated by the fact that almost no one considers the risk that Hurricane Isaac would have posed to New Orleans if their new Hurricane Storm Damage Risk Reduction, HSDRR, system had not been in please when Isaac made landfall. 

Furthermore, I believe that countries such as Holland will soon take serious measures to mitigate the risks of ASLR to their country this century; no matter what the majority of SLR experts believe at the moment.  It takes too long to provide adequate local inundation defenses against ASLR for large cities (such as post-Super-Storm Sandy New York City, let alone countries like Holland) to wait until the majority of researchers (including those in the IPCC WG1) recognize the risks of ASLR, before taking appropriate local adaptive action. 

I am sorry to say that I believe that by the end of this century coastal defense will be the largest industry on Earth, if we continue on our current BAU path.

[wili]

Good points, ASLR. But don't you think that a major part of adapting in many places will just be moving away from the coast? Do you think Bangladesh is going to build a giant wall along their entire coast?

I agree that, in many places that can afford it, people will often try to mitigate slr by building such defenses, partly because, if they think it will be just a foot or two in the next few decades, building a small wall seems easier than moving a city. But all these walls will have to be built higher and higher going forward. It should be clear that if the cost of the full eventual wall was to be figured in now, most places would determine that just moving away from the coast would be cheaper. But, as with most thing, the future costs are mostly hidden from us or can be discounted in various ways.

[Lennart van der Linde]

ASLR, wili,
At RealClimate Perwis pointed out that the worst case, according to one expert (was it Hansen?), now seems to be about 15 meter of SLR by 2300. This would imply a maximum rate of SLR of at least 50-70 cm/decade for at least several decades at some point during the coming centuries.

Most experts apparently think this is implausible, but on what grounds, and with what confidence, considering the unprecedented magnitude of a BAU-forcing? And is adaptation, other than retreat, to such rates of SLR really possible even in rich countries?

[Lennart van der Linde]

Also: 15 meter of SLR by 2300 would maybe imply say a 7 meter/century rise for the rest of the millennium, so maybe about 64 meter by the year 3000. Hansen thinks this would be possible under BAU.

What low-lying city/country could defend itself for more than a century against such SLR?

[wili]

Geoff, good set of links.

It is unfortunate that the NS article has no link to the article it seems to be reporting on. I have had no luck finding it with searches either. Perhaps the article has not yet been published?

[Neven]

What low-lying city/country could defend itself for more than a century against such SLR?

Atlantis? 

[wili]

[AbruptSLR]

Lennart/wili,

All that I can say is that the USACE invested about $17 Billion to build the new HSDRRS about much of Greater New Orleans that is designed to resist a combined storm surge and SLR, by 2057, of just under 7m.  Furthermore, analyses for such storm surge systems normally demonstrate a cost/benefit ratio of between 4 to 6 times investment.  Thus in the future cities that can afford such systems will likely pay to buy a century's worth of safety.  When you consider that the global insurance industry has assets of over $30 trillion, you begin to understand how much modern society is willing to pay for safety.  Also, economic development is currently accelerating in coastal areas, so instead of retreating, many people are advancing into high inundation risk areas.  Finally, I believe that if society does not learn to limit carbon emissions by 2100, then the economic destruction from climate change with reduce the carbon emissions by default.

[bligh8]

Neven, Apparently your not alone in your thinking...

http://www.nytimes.com/2013/06/12/nyregion/bloomberg-outlines-20-billion-plan-to-protect-city-from-future-storms.html?_r=0

Mayor Bloomberg of NYC has allocated 20 billion to harden and raise the vertical protection of NYC. he also repeatedly said that this was an opening salvo in GW issue and likely cost much more in the future. His argument about the economic balance sheet was as you suggested.

[Lennart van der Linde]

ASLR,

For the coming century you may well be right, as also suggested in this paper by Nicholls et al (2010):
http://rsta.royalsocietypublishing.org/content/369/1934/161.full

They speak about adaptation 'pessimists' and 'optimists':
"The ‘pessimists’ seem to take it as read that adaptation will either fail or people will not even try to adapt. In contrast, the ‘optimists’ appear overly confident that benefit–cost approaches describe human behaviour in response to threats such as sea-level rise."

Beyond 2100 it seems less clear to me that adaptation will be the preferred option, or even technically or economically possible, if SLR by that time is so fast that cities/countries will need to adapt almost continuously (and not only to SLR of course). Miami/Florida for example seems almost impossible to defend, even in this century, due to its porous geological foundation:
http://thinkprogress.org/climate/2013/06/23/2199031/scientist-miami-as-we-know-it-today-is-doomed-its-not-a-question-of-if-its-a-question-of-when/

Meanwhile probably some cities/countries will adapt in time to prevent big disasters from happening, but others will likely be too late, so disasters wil probably be bigger and more frequent.

Also protection costs will rise disproportionately with higher sea level, according to Nicholls et al:
"[A] dike required in response to a 2m rise in sea level is assumed to be four times the cost of that required for a 1m rise in sea level."

Since we can't simply assume the world will become richer and richer, due to both climate change and resource depletion, these rising adaptation costs will at some point become an unbearable burden on public budgets. The less we invest in mitigation the sooner we will probably reach this point.

But at the same time: the less we invest in adaptation, the more and bigger disasters will happen. So we need to invest more now, in both mitigation and adaptation, to prevent costs from becoming unbearable further into the future.

[ggelsrinc]

Hansen and Alley talk about tipping points, but let me paint a different picture. We all live around areas where tipping points can be proven. Sadly, the first thing that comes to my mind is a cemetery. We may think we stand on solid ground, but the soil beneath our feet creeps due to gravity. If you have ever looked at old glass, you will notice it's thicker on the bottom than the top. If you look at old structures built on a slope, you will notice their foundation is changed over time. Getting back to the concept of tipping point and cemeteries, find a cemetery near you on sloping ground and notice the position of the tombstones/gravestones. I've seen well constructed barns made of timbers more than a foot thick laid on solid foundations moved by soil creep and many other things to give an example. It just takes time.

How many ice shelves are left in the Northern Hemisphere, compared to the historical record of what their areas once were? When ice shelves stop buttressing a glacier, that glacier will speed up no matter what the temperature is, because of gravity. The nature of ice is many times more plastic than soil.

I'm not a Doomsdayer and I don't believe Hansen or Alley is, because I think we still have time. The gravity of this situation is we have a big problem on our planet and we need to get off our asses to fix it. (Sorry about the French, Neven)

 

[Lennart van der Linde]

Quoted from RealClimate in relation to the difference in amounts of ice in the Northern Hemisphere during the last deglaciation and now:
“[T]here was about 10 times the amount of ice on the Northern hemisphere during the multimeter sea level rise intervals of the deglaciation”.

My response: on the other hand, globally there was only about 3 times more ice on the planet then as compared to now. And then the planet was warming on average about 0.005 degrees C per decade as compared to about 0.15 degrees per decade now. So this is about 30 times faster and will likely accelerate, as more and more positive feedback kick in.

If it would warm 5 degrees this century, which seem quite possible, that would be about 100 times faster than the average rate during the last deglaciation, although I suppose ocean heat content rises somewhat slower.

The warming then was instigated by higher insolation in the Northern hemisphere, where most of the ice was. The warming today is caused by higher CO2, which works globally, including in the Southern Hemisphere, where most of the ice is now.

The total forcing back then was about 6-7 W/m2, including slow positive feedbacks, while the initial orbital forcing was about 20 times smaller, according to Hansen. The initial CO2/GHG-forcing now is already about 3 W/m2, so about 10 times higher then 20.000 years ago, and growing rapidly, if I understand correctly.

This has been partly masked by a negative human aerosol forcing so far, but that masking will likely become smaller as more people will demand cleaner air. And slower positive feedbacks may already be starting to have an additional forcing now and a growing one during this century.

All in all it seems quite possible that the forcing this century and after will be substantially stronger than during the last deglaciation. So less ice to melt now does not necessarily mean SLR will be slower than in the past, it seems, once it gets up to speed, and if we fail to reduce our emissions sufficiently.

[AbruptSLR]

Lennart & ggelsrinc,

All very good points; and I must add that I am genuinely concerned that methane from: hydrofracking, permafrost, and marine hydrates, could get out of control if we stay on a BAU pathway.  Specific examples of my concerns include:

(a) China has the largest shale gas reserves in the world and western old companies are transferring technology as fast as they can; but I am believe that methane leaks during both drilling and transport will be difficult to control in China (note that with leaks hydrofracking is as bad or worse than coal).  Plus if China converts their coal fired power plant from coal to methane the will likely be able to reduce their CO₂ emissions while maintaining the same global warming potential (GWP); and as the methane fired power plant will have less air pollution, the decrease in local albedo will increase radiative forcing further.

(b) The RCP pathways (particularly RCP 8.5) do not include the 2% methane emissions from permafrost degradation; and furthermore most current models use a GWP of no more than 25 for methane while due to atmospheric chemistry its actual GWP is at least 35.  This means that the radiative forcing from permafrost degradation will be at least 70% higher than most GCM projections consider.

(c) I am concerned that this winter we saw in increase in CDW (Circumpolar Deep Water) and AABW (Antarctic Bottom Water) temperatures contribute to new emissions of methane from marine hydrates in portions of the Southern Ocean (which I believe results in the atmospheric methane concentration increasing over Antarctica, during the austral winter, when the very cold atmospheric temperatures decrease the rate of chemical reactions that breakdown the methane).  Furthermore, I am concerned that such an increase in atmospheric methane concentration over Antarctica, will increase the speed of circumpolar Westerly winds, which will increase coastal up-welling of CDW (circumpolar deep water), which increase the melting rates of both ice shelves and ice melting along the grounding lines of key marine glaciers (both in the WAIS and the EAIS).

(d) I will not talk about the Kraken of potential methane release from Arctic marine hydrates; which has been extensively covered by others.

I will keep my fingers crossed that we get off the BAU path sooner rather than later because if we do not then we could be on track for a 8^oC mean global temperature rise by 2100.

[AbruptSLR]

Further to my concerns about methane, please see the following linked reference:


http://www.pnas.org/content/early/2013/11/20/1314392110.abstract



Scot M. Miller, Steven C. Wofsy, Anna M. Michalak, Eric A. Kort, Arlyn E. Andrews, Sebastien C. Biraud, Edward J. Dlugokencky, Janusz Eluszkiewicz, Marc L. Fischer, Greet Janssens-Maenhout, Ben R. Miller, John B. Miller, Stephen A. Montzka, Thomas Nehrkorn, and Colm Sweeney, 2013, "Anthropogenic emissions of methane in the United States"; PNAS, November 25, doi: 10.1073/pnas.1314392110

"Abstract
This study quantitatively estimates the spatial distribution of anthropogenic methane sources in the United States by combining comprehensive atmospheric methane observations, extensive spatial datasets, and a high-resolution atmospheric transport model. Results show that current inventories from the US Environmental Protection Agency (EPA) and the Emissions Database for Global Atmospheric Research underestimate methane emissions nationally by a factor of ∼1.5 and ∼1.7, respectively. Our study indicates that emissions due to ruminants and manure are up to twice the magnitude of existing inventories. In addition, the discrepancy in methane source estimates is particularly pronounced in the south-central United States, where we find total emissions are ∼2.7 times greater than in most inventories and account for 24 ± 3% of national emissions. The spatial patterns of our emission fluxes and observed methane–propane correlations indicate that fossil fuel extraction and refining are major contributors (45 ± 13%) in the south-central United States. This result suggests that regional methane emissions due to fossil fuel extraction and processing could be 4.9 ± 2.6 times larger than in EDGAR, the most comprehensive global methane inventory. These results cast doubt on the US EPA’s recent decision to downscale its estimate of national natural gas emissions by 25–30%. Overall, we conclude that methane emissions associated with both the animal husbandry and fossil fuel industries have larger greenhouse gas impacts than indicated by existing inventories."

[AbruptSLR]

Also,

The following link cites that the ESAS is emitting 17 millions tons of methane into the atmosphere each year, twice the amount of methane previously estimated.

http://www.scienceagogo.com/news/20131025184929.shtml

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2007.html


Ebullition and storm-induced methane release from the East Siberian Arctic Shelf; Natalia Shakhova, Igor Semiletov, Ira Leifer, Valentin Sergienko, Anatoly Salyuk, Denis Kosmach, Denis Chernykh, Chris Stubbs, Dmitry Nicolsky, Vladimir Tumskoy & Örjan Gustafsson; Nature Geoscience, (2013), doi:10.1038/ngeo2007

Abstract
"Vast quantities of carbon are stored in shallow Arctic reservoirs, such as submarine and terrestrial permafrost. Submarine permafrost on the East Siberian Arctic Shelf started warming in the early Holocene, several thousand years ago. However, the present state of the permafrost in this region is uncertain. Here, we present data on the temperature of submarine permafrost on the East Siberian Arctic Shelf using measurements collected from a sediment core, together with sonar-derived observations of bubble flux and measurements of seawater methane levels taken from the same region. The temperature of the sediment core ranged from −1.8 to 0 °C. Although the surface layer exhibited the lowest temperatures, it was entirely unfrozen, owing to significant concentrations of salt. On the basis of the sonar data, we estimate that bubbles escaping the partially thawed permafrost inject 100–630 mg methane m−2 d−1 into the overlying water column. We further show that water-column methane levels had dropped significantly following the passage of two storms. We suggest that significant quantities of methane are escaping the East Siberian Shelf as a result of the degradation of submarine permafrost over thousands of years. We suggest that bubbles and storms facilitate the flux of this methane to the overlying ocean and atmosphere, respectively."

[wili]

Thanks for these links, ASLR. Note that the Shakhova article is now a subject of a thread over at the blog: http://neven1.typepad.com/blog/2013/11/and-the-wind-cries-methane.html

(Though I'm currently having some trouble signing in there. Anyone else having similar difficulty?)

[AbruptSLR]

wili,

Thanks for the link to the ASIblog.  I do check that thread regularly, but I do not post there due to lack of time.  Certainly, methane from Arctic marine hydrates (most significantly from the East Siberian Arctic Shelf) is one of the largest wild cards about methane.  Nevertheless, the following links confirms that atmospheric methane concentration is currently increase (see NOAA Mauna Loa data), that even the conservative IPCC WG1 AR5 report aknowledges that the 100-year GWP for methane is currently 34 (not 25 as previously thought), and that the USA is currently leaking methane at about a 3% rate while if methane leaks at a rate of 2.7% it is equivalent to coal (imagine what the leakage rate for methane will be in the future when the rest of the world, including China, gear up for the hydrofracking boom):

http://www.esrl.noaa.gov/gmd/dv/iadv/graph.php?code=MLO&program=ccgg&type=ts

http://thinkprogress.org/climate/2013/11/25/2988801/study-methane-emissions-natural-gas-production/

http://thinkprogress.org/climate/2013/10/02/2708911/fracking-ipcc-methane/

[AbruptSLR]

The information at the following links give an idea that global warming will accelerate when the current ENSO hiatus period ends:

http://www.skepticalscience.com/pacific-ocean-global-warming-puzzle-Kosaka-Xie.html

http://www.theguardian.com/environment/climate-consensus-97-per-cent/2013/sep/03/global-warming-pacific-ocean-puzzle-piece

[Lennart van der Linde]

To return to Horton et al: in the conclusion it says that 13 experts (out of 82) think there's about a 17% chance that SLR by 2100 could be more than 2 meters in the RCP 8.5 scenario, with about 6 meters as highest estimate. So it seems about 16% of the experts think there's a substantial risk of 2 meters or more in the worst-case.

Figure 2 of the paper shows that 5 out of 82 experts think there's about a 5% chance that SLR by 2100 could be 3 meters or more in this BAU scenario, with the highest estimate about 7 meters. So it seems about 6% of the experts think there's some risk of more than 3 meters of SLR by 2100 in the worst-case.

But even in the strong mitigation scenario of RCP 3 three experts out of 84 think there's about a 5% chance of more than about 1.5 meters of SLR by 2100., with the highest estimate around 2 meters. So it seems almost 4% of the experts think that even in the best case there's some risk of more than 1.5 meters of SLR by 2100.

About 50% of the experts think that in this best case there's about a 17% chance of more than 0.6 meters of SLR by 2100 and about a 5% chance of more than 0.7 meters. So even in the best case there seems to be a significant risk of more than 60 cm of SLR around 2100.

Some more results from figure 2:

- 7 out 72 experts think there's about a 5% chance of 7 meters or more by 2300 under BAU, with the highest estimate about 15 meters.

- 5 out of 72 experts think there's about a 17% chance of 6 meters or more by 2300 under BAU, with a highest estimate of almost 10 meters.

- 3 out 74 experts think there's about a 17% chance of 3 meters or more by 2300 even in the best case, with 3.5 meters as highest estimate.

- 3 out of 74 experts think there's about a 5% chance of 4 meters or more by 2300 in the best case, with almost 8 meters as the highest estimate.