Experts have a say on sea level rise

The recent IPCC report estimated sea level rise (SLR) thus:

SLR by 2100_cropped

For the scenario RCP8.5 (the most likely) the rise by the year 2100 is 0.52 to 0.98m, with medium confidence.

A new study (Horton, Engelhart and Kemp) asked experts in the subject for their view. For the RCP8.5 scenario they came up with 0.7 to 1.2m, as shown here:


Fully 65% of experts expect SLR greater than the IPCC forecasts.

The dotted lines on that graph represent NOAA projections of December 2012.

Meanwhile if, against the odds, we can hold temperature rise to about 2°C, then what happened during the last interglacial, the Eemian, has some relevance. This from the IPCC report:

There is very high confidence that maximum global mean sea level during the last interglacial period (129,000 to 116,000 years ago) was, for several thousand years, at least 5m higher than present, and high confidence that it did not exceed 10 m above present. During the last interglacial period, the Greenland ice sheet very likely contributed between 1.4 and 4.3 m to the higher global mean sea level, implying with medium confidence an additional contribution from the Antarctic ice sheet. This change in sea level occurred in the context of different orbital forcing and with high-latitude surface temperature, averaged over several thousand years, at least 2°C warmer than present (high confidence).

It’s counter-intuitive, but sea level rise is not uniform over the globe. The NOAA study gives us this interesting image:

Global SLR_cropped_580

Our part of the globe does not fare well. There is a real pile up to the north of us, where the Philippines cops heightened SLR as well as (probably) an increased incidence of strong typhoons.

It’s not very noticeable, but the north-eastern seaboard of the United States is also a hotspot, from North Carolina northwards. Fascinating, then, that while New York is preparing for sea level rise North Carolina has legislated that it won’t.

Preparations for SLR are for the time being verboten. Only socialists and cowards prepare for the worst. They prefer to place their faith in God rather than science.

In Climate clippings 89 (Item 6) we noted Queensland’s latest effort in pushing responsibility onto local governments for SLR. This article sees this as a national trend and suggests we, the taxpayers, will pay.

Meanwhile expect more scenes like we had in Surfers Paradise in May 2013:


The Horton and NOAA studies would have been to late to be considered in the IPCC review. Yet another paper, by Anders Levermann et al of the Potsdam Institute would also have been too late. He looked the long term commitment, over thousands of years, implied in each degree of temperature rise. The graphs shows the 2000 year commitment form various sources:

levermann2013_300Sea level rise over 2000 years from: (a) ocean warming, (b) mountain glaciers, (c) Greenland, (d) and Antarctic ice sheets. The total sea level commitment (e) is about 2.3m per degree of warming above pre-industrial.

This paper took into account paleo-climate information and surprises me with its conservatism.

Take for example this 2009 study:

The new record reveals a systematic equilibrium relationship between global temperature and CO2 concentrations and sea-level changes over the last five glacial cycles. Projection of this relationship to today’s CO2 concentrations results in a sea-level at 25 (±5) metres above the present. This is in close agreement with independent sea-level data from the Middle Pliocene epoch, 3-3.5 million years ago, when atmospheric CO2 concentrations were similar to the present-day value. This suggests that the identified relationship accurately records the fundamental long-term equilibrium behaviour of the climate system over the last 3.5 Million years.(Emphasis added)

That makes sense with this graph from Archer (about 2006):


It makes sense if the large continental ice sheets melted with about 5-6C warming at the rate of about 20m per degree that the remaing ice may go at the lower rate, averaged over the whole of about 15m per degree.

It is possible that the East Antarctica ice sheet worth about 59m of SLR has become very stable with a pile of ice 4km high and an average temperature of -39°C. Yet it is vulnerable around the fringes.

Much depends on what happens when the ice sheet melting starts to go critical. The climate has never been pushed as it is now, outside perhaps major asteroid strikes. I wouldn’t be surprised if estimates of ice sheet decay move around a bit over the years. Meanwhile we have plenty to worry about with homes, commercial buildings, major infrastructure and fertile river deltas in the world vulnerable to centimetres rather than metres of SLR.

Yes, and once again we are moving on from the IPCC report before the ink is dry. Nevertheless it will be quoted as holy writ rather than a reference point for the next seven years.

Here’s an image of Asian cities threatened by SLR, from a 2009 UNEP report:

UNEP Asian cities

10 thoughts on “Experts have a say on sea level rise”

  1. That, Terangeree, is what all of the panic over refugees is about, global warming producing flotillas of millions.

  2. Read an interesting article, “High and Dry” in the print version of New Scientist (4 May 2013). It predicts that, if the Greenland ice sheet melts, sea levels along the Greenland coast will fall by something like 100 metres. (Yes, fall.)
    The explanation is that

    any large mass on the earth’s surface exerts a significant gravitational pull on any water surrounding it.

    Even the the north of Scotland would see a 3 meter drop.
    Changing wind and current patterns will also have an effect on relative sea level rise around the world.
    Ongoing rebound after the last ice age will also have an effect. Keep in mind that places like New York that was outside of the ice sheet actually rose during the ice age (and are now sinking) because the weight of the ice pushed ground out and up from the area covered by the ice sheet.
    Buy water front property with title down to the water’s edge in Northern Scotland. Sell inNY.

  3. I would prefer,when I am conservation minded to dwell on engineering works like Abbot’s Point or whatever it is called.To be just opposed to it is a stuck in the mud reality means,one couldn’t get round to deciding that drenching should be a no-no,and some other simpler,proposals could in fact be cheaper.One of the contributors here talks about May and Scotland,whereas,Palmer is here now and approved,and I can tell you this.Even if I agreed with you here a 100%,as someone who has outlined design engineering before and had it taken up,I suffer a lot of angst hurt,depression about that because of outcome.I feel,only enlightened by the meerest of details,that Palmer has got it through too easy.That is both the mining matter,and the dredging matter,whereas the rail becomes a permanent thing for a long time,that does nothing but move coal ! Whereas a port doesn’t need to be dredged when concrete blocks can settle onto the port sea level.Hydraulics can lift up ships and lower them,swing them round to adjust to very harsh conditions .Concrete blocks themselves could be on definable and real sea rails..And there is no prospect that the ocean and seas are going to get less active. So why do these designers,just commit design to dredging!?If there is no way to penalise such designing because it is jointly owned by business and government,then, the equal of a penalty to the professional groups allowing this garbage design needs enacting.

  4. Emotional state lent itself to drenching rather than dredging.I am not doing well fighting against the senility that government and media decide is positive.There maybe other errors.

  5. John D, now you mention it I do recall that New Scientist article.

    BTW the Wikipedia map shows New York just within the range of the ice sheet and this article confirms that it reached that far.

    The diametre of the earth is about 12,700 km so sea level variations need to be seen in that context.

  6. The differential patterns of sea level rise in the Pacific over the last 20 years (the period covered by the map) are largely a product of the cluster of La Nina events since 2007 (during La Nina years, easterly winds are stronger through the tropical Pacific, and water tends to “pile up” against the ocean’s western side). There’s no particular reason to expect that pattern to persist into the future.

  7. Makes sense, Blair.

    OTOH I think the increased SLR on the NE coast of the US may be related to Greenland melting, but it’s a long while since I read about that.

  8. Correct me if I am wrong but aren’t the gravitational effects of large masses of (impounded) water well understood from studies on large dams? Thanks for the heads-up on falling sea-levels, John D.

    Mention has been made a few times about adverse changes in sea-water pH – but what will be the likely effects on weather and on marine ecology from the diluted salinity of sea-water?

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