GIS contribution to SLR doubling every 5 years or so

[wili]

This from sidd at RC. Apologies if it's already been posted elsewhere:

New paper on DEM and mass waste for Greenland and Antarctica from Cryosat-2

http://www.the-cryosphere-discuss.net/8/1673/2014/tcd-8-1673-2014.html

Greenland: Mass loss doubled in between the periods 2003-2008 and 2011-2012
The latter period saw rates of 353 +/- 29 Km^3/yr or approx 1mm/yr sea level rise

My rough estimation is that this rate (or a bit worse) of increase would lead to more than a meter of sea level rise by about mid century. Should we expect then the rate to keep accelerating till it's all gone? Or will the rate rise then fall again in a Gaussian bell curve?

[icefest]

I'd expect it to be relatively negatively skewed, as when the height of the sheet drops, melting will speed up.

I'd also expect some ice to be left over on the higher mountains even when the sheet collapses.

[wili]

"when the height of the sheet drops, melting will speed up"

That's what I would assume, too. I can't think of many negative, damping feedbacks that would act to slow down the rate of ice melt till it was all (or almost all, as you say) gone.

[crandles]

I have no idea how powerful a feedback an open Arctic Ocean in autumn would be. Lots of extra snowfall? Hasn't stabilised things so far but perhaps small extra bits of open ocean aren't near enough to Greenland?

If that isn't enough to slow things down, then I would tend to assume we are still a long way from the inflection point where rate of mass loss switches to decelerating (for the last time?).

But if Hanson has seen a doubling in 5 years but then proceeds to talk projections of doubling every 10 years then should I believe Hanson rather than assuming we are still a long way from that inflection point?

[sidd]

" ... when the height of the sheet drops, melting will speed up."


Indeed: see Gregoire(2012)  doi:10.1038/nature11257
I attach Fig 2d) and 3

[sidd]

I should add that I expect the mechanism of saddle collapse in Gregoire to apply to the saddle in Greenland at 67N separating the North and South Domes.

sidd

[Shared Humanity]

I should add that I expect the mechanism of saddle collapse in Gregoire to apply to the saddle in Greenland at 67N separating the North and South Domes.

sidd

Thank you.

This is why I come here.

[TerryM]

Sidd
The Greenland saddle will exacerbate an already bad situation. Winter storms this year in England played havoc with some of the coastal rock formations & I expect rapid melt and outflow to do the same to Greenland's coasts. The thousand year estimates I believe have been made with the assumption that the fjords will remain approximately as they now are and that the glacial grounding lines are grounded on solid rock as opposed to gravel.
If either of these assumptions proves unfounded SLR could be higher than even Hansen's worst case scenario.
Terry

[tombond]

Using NASA data taken from their graph at http://climate.nasa.gov/key_indicators also calculates as a doubling time of about 5 years for the combined Antarctica and Greenland ice sheets.

Hansen has calculated a 1 metre sea level rise (SLR) by 2045 for a 5 year polar ice melt doubling period, 2055 for a 7 year doubling period and 2067 for a 10 year doubling period.  See www.columbia.edu/~jeh1/.../20121226_GreenlandIceSheetUpdate.pdf‎

These predictions are much earlier than the IPCC AR5 BAU ‘extreme’ SLR prediction of 0.98m by 2100.

As ice melt rates are the biggest risk for coastal planning policy makers it makes good sense to continually monitor the ice melt acceleration rates as the priority input into sea level rise predictions. 

If the current polar ice melt acceleration rates are maintained, the government/community will have some ‘early warning’ of abrupt sea level rise and hopefully some lead time to better plan and manage a staged retreat from the existing coastline.

Conversely if the current melt acceleration rates slow then government/community will have the certainty of more lead time to plan and act. 

Either way, all coastal planning decision making would be informed and based on real scientific observations with no ‘surprises’. 

[Shared Humanity]

The most frightening aspect of doubling is what it means for the 2nd half of the century. Even if we take the most conservative of these predictions, a ten year doubling rate, this suggests we have a steady growth rate of 7% per year in melt.

This ten year doubling results in 1 meter sea level rise in  40 years or by 2067. A similar steady growth rate for the remainder of the century would mean a sea level rise of an additional 2 meters by the first decade of the next century.

What impact will a 3 meter sea level rise have?

[sidd]

For impact of SLR here are some references I found useful. I dont agree with a bunch, but there is data in these. I know I have more, but i am on the road, and not easy access to my full reference lists.

"Hypsographic demography: The distribution of human population by altitude"
Cohen(1998) Proc. Natl. Acad. Sci. USA Vol. 95, pp. 14009–14014, November 1998

"A significant percentage of the low-elevation population lived at moderate population densities rather than at the highest densities of central large cities. Assessments of coastal hazards that focus only on large cities may substantially underestimate the number of people who could be affected."

"Sea-Level Rise and Its Impact on Coastal Zones," Robert J. Nicholls, et al., Science 328, 1517 (2010)
DOI: 10.1126/science.1185782

This is a review article. Points out that subsidence is a huge problem due primarily to groundwater depletion and drainage; that in Tokyo, Shanghai and Bangkok have seen subsidence of 5,3 and 2 meters. Says that in many cases coastal populations can be successfully defended (not my view) and concludes with call for adaptation. Quite optimistic.

"Uncertainties in Measuring Populations Potentially Impacted by Sea Level Rise and Coastal Flooding"
Mondal et al. (2012) doi:10.1371/journal.pone.0048191

This is open access. Supplementary material is very useful, has a list of major city population by elevation. The main paper has detailed maps for many areas.

"Sea-level rise and its possible impacts given a 'beyond 4°C world' in the twenty-first century"
Robert J. Nicholls et al., Phil. Trans. R. Soc. A 2011 369, doi: 10.1098/rsta.2010.0291, (2010)

open access i think.
Tol is a author, and Nicholls thinks adaptation can work more effectively than in my view. Nevertheless,  is forced to admit:

" ... with the real risk of the forced displacement of up to 187 million people over the century (up to 2.4% of global population). "

goes on to sugarcoat:

"This is potentially avoidable by widespread upgrade of protection, albeit rather costly with up to 0.02 per cent of global domestic product needed, and much higher in certain nations. The likelihood of protection being successfully implemented varies between regions, and is lowest in small islands, Africa and parts of Asia, and hence these regions are the most likely to see coastal abandonment."

In short, Bangladeshis will drown first, as the richer nations build dikes higher, and higher and higher, before giving up.

uses the DIVA model, which is too close for my liking to the FUND model that Tol misuses, cuts off high end at 2m, ignores dike maintenance, but has useful info.

sidd

[sidd]

An additional paper

Hallegate(2013)

DOI: 10.1038/NCLIMATE1979

"Future flood losses in major coastal cities"

uses the DIVA model, but i trust em more than Tol, Nicholls is an author, but seems to have recanted a bit.

"Even if adaptation investments maintain constant flood probability, subsidence and sea-level rise will increase global flood losses to US$60–63 billion per year in 2050. To maintain present flood risk, adaptation will need to reduce flood probabilities below present values. In this case, the magnitude of losses when floods do occur would increase, often by more than 50%, making it critical to also prepare for larger disasters than we experience today."

Giant numbers for average annual loss. nice data in supplementaries.

sidd

[Lynn Shwadchuck]

It seems this thread is dormant even though there's a major development. (I see that idunno posted a Physorg article on the paper under a Greenland topography topic that isn't getting much attention.)

The supplements (all the visuals!) to the paper: http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf

Until this new data set was released, like yesterday, it was widely thought by many professional glacier scientists, that once all Greenland's glaciers which have been accelerating their speed of retreat as the warming ocean lapped at their edges, they would halt on solid ground. The vastly improved mapping of the topography of Greenland's bedrock now proves that the channels – extensions of the fiords where the glaciers flow – are very deep under the glaciers, far inland. This means the effect of sea water on the glaciers will continue through this century. Dr. Richard Alley, who specializes in the West Antarctic Ice Sheet, has shown that its collapse is now 'unstoppable', indicating that we really can't afford not to make an all out effort to roll back greenhouse gases and stop Greenland's melt. In general, it means the difference between being committed to 10 feet of sea level rise this century (hard to adapt to) and 33 feet (impossible to adapt to).

Dr. Jason Box is interviewed by Peter Sinclair: