Ballad of broken seas

by Gareth on August 3, 2008

CRW_3037.jpg The Ministry for the Environment released an updated Coastal Hazards and Climate Change manual for local government last week, based on work done by NIWA. It incorporates the latest NZ thinking on where sea-levels are heading. If you’re planning to build something that has to last until the end of the century (and that covers a lot of coastal infrastructure), you should allow for half a metre of sea-level rise, and consider the consequences of an increase of up to 80cm. The report says:

For planning and decision timeframes out to the 2090s (2090–2099):

a. a base value sea-level rise of 0.5 m relative to the 1980–1999 average should be used, along with

b. an assessment of the potential consequences from a range of possible higher sea-level rises (particularly where impacts are likely to have high consequence or where additional future adaptation options are limited). At the very least, all assessments should consider the consequences of a mean sea-level rise of at least 0.8 m relative to the 1980–1999 average.

For planning and decision timeframes beyond 2100 where, as a result of the particular decision, future adaptation options will be limited, an allowance for sea-level rise of 10 mm per year beyond 2100 is recommended (in addition to the above recommendation).

Local authorities have a duty to understand this stuff (under the RMA and other legislation), so the report is highly detailed. If you’ve ever hankered after an in-depth understanding the processes that underlie storm surges, beach (and bach) erosion, tidal ranges and tsunamis, there’s no better place to start. If you want to see what impact that sort of rise might have on your area, try Global Warming Art’s excellent Google Maps mashup Sea Level Rise Explorer, or check NASA JPL’s new climate change site for the global sea level picture [Flash required].

Also released last week: the edited highlights (with pretty pictures) version of the Preparing For Climate Change guidance manual published last May which incorporates NIWA’s latest climate projections for NZ. Essential. And free.

{ 11 comments… read them below or add one }

John Key August 3, 2008 at 9:42 pm

I just checked that Google map thingo – Its a close one, but looks like Rodney Power station will narrowly escape becoming submerged under the ocean… phew!!

See yous after the election

John

gareth August 3, 2008 at 10:31 pm

That would where you plan to burn Mr Hide?

Before the tide comes in, obviously…

Carol August 3, 2008 at 10:50 pm

Thanks, Gareth, the Guidance Manual is an excellent thing indeed.
I went to a workshop on this last week. My understanding is that the projected sea level rises used for the planning timeframes that you mention above are based on the IPCC’s best estimates, adapted for local conditions. Some subsequent science since the 4th assessment report cut-off suggests that considerably more sea level rise is a distinct possibility – the range quoted by Rahmstorf is 0.5-1.4 metres by 2100 above the 1990 level.
Rahmstorf, S., 2007, A semi-empirical approach to projecting sea level rise. Science, 315, 368-370.
Rahmstorf, S., et al., 2007, Recent climate observations compared to projections. Science, 316, 709.

gareth August 3, 2008 at 10:58 pm

Rahmstorf’s paper is cited in the manual. For what it’s worth, I think just under a metre by the 2090s is a reasonable position for planners to take at the moment. Over the next few years, that might change. Personally, I fear Meltwater Pulse 1a rates if Arctic warming speeds up (see HT passim)

CobblyWorlds August 4, 2008 at 5:54 am

The Rahmstorf papers Carol cites are available without paywall from Rahmstorf’s page here. Top 3 bullet points.

From a quick Google; Rodney Power station is a fossil fuel installation. The lifetime of such infrastructure measured against likely timescales for sea level rise (SLR) should not mean coastal siting is problematic.

However here in the UK we’re on the verge of a resurgence of our nuclear industry, and from what I can see they’re using the IPCC SLR range plus planned reactor lifetime as a guide to siting. Historically virtually all of our nuclear plants have been coastal.

In respect of nuclear power I really think plants should be sited assuming possible millenial scale SLR (10 metres or so?). We may plan to decomission and leave as green-field, but we should consider the risk that in the future entombment may be the only economically viable option.

Just up the coast from where I live is Heysham, here is a photo. There are 4 reactors, 2 in each unit, and it’s being suggested another could be built there in the coming tranche of nuclear expansion. You can get some idea of the sea level rise issue if you look at the water in the above photo – that water is the sea.

Carol August 4, 2008 at 10:00 am

Rahmstorf, in the first of the papers cited above, says that ‘.. the uncertainty in future sea-level rise is probably larger than previously estimated.’
As if it wasn’t already challenging enough being a planner..

CobblyWorlds August 4, 2008 at 10:12 pm

Carol,

These things can be bounded. I couldn’t find it this morning but I have read a pretty convincing rebuttal of Hansen’s 5 metre SLR at least with regards Greenland. Basically the topography of Greenland means that glacier flow is restricted by the coastal mountain ranges so they act as a bottleneck. Then the mass of the ice is up on top, where it’s colder. So overall whilst Greenland will probably not last millenia (as indicated in earlier IPCC reports) on policy/planning timescales it’s possible to reason an upper bound that implies less than metres of SLR by 2100.

The West Antarctic Ice Sheet is a whole different matter. That said, I live just 10 metres above sea level, and would not be worried even if I was going to live till 2200.

cindy August 4, 2008 at 10:48 pm

Interesting that NIWA hasn’t taken into account what the IPCC finally concluded on sea level rise.

The AR4 Synthesis Summary for Policymakers actually removed the upper limit to sea level rise because of the many uncertainties in various projections.

“Because understanding of some important effects driving sea level rise is too limited, this report does not assess the likelihood, nor provide a best estimate or an upper bound for sea level rise.”

“The projections do not include uncertainties in climate-carbon cycle feedbacks nor the full effects of changes in ice sheet flow, therefore the upper values of the ranges are not to be considered upper bounds for sea level rise. They include a contribution from increased Greenland and Antarctic ice flow at the rates gobserved for 1993-2003, but this could increase or decrease in the future.”

Steve Bloom August 5, 2008 at 11:22 pm

These results from the Eemian indicate that in the range of 2 meters/century is possible. See also this interview with the lead author. “I think that ultimately we will find that we best prepare for rates of 1.5 to 2 m per century, or more, to be on the safe side. Nature is telling us something: sea-level rise can be very rapid indeed, and we underestimate it at our own peril…”

HarryTheHat August 6, 2008 at 1:31 am

Jeez! Why don’t you people worry about something that is likely within your lifetime, or that of your children’s (assuming you have any), rather than unlikely for 100s or 1000s of years? Worry about the world population in just 10 years, worry about mid-east war, worry about religious fundamentalism, worry about the likelihood of global cooling – at the same time as massive population growth! Why don’t you get real, rather than scrubbing around in things that either aren’t happening, or are unlikely to for many, many years to come?

…and please try and come up with constructive arguments, rather than just abusing me (or calling me a troll, Cobblers) if you can’t just avoid me :)

CobblyWorlds August 6, 2008 at 7:32 am

Steve,

I agree “metres” (i.e. 2m or more) of SLR by 2100 are possible. My last sentence above should have read: “it’s possible to reason an upper bound that implies less than 5 metres of SLR by 2100.”

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