# Sea level rise

I’m getting a bit annoyed with people pushing over-inflated estimates of SRL in the near future. Richard Alley apparently said There is no consensus on how much Greenland’s ice will melt in the near future, Dr. Alley said, and no computer model that can accurately predict the future of the ice sheet. Yet given the acceleration of tidewater-glacier melting, a sea-level rise of a foot or two in the coming decades is entirely possible, he said (though in his defence its not in literal quotes).

But the current rate is 3 mm/yr. If that doubles to 6 mm/yr, then over two decades that would be 120 mm. Which is well short of even 1 foot. So… anyone want to bet on at least 1 foot in 20 years (or could we say 6 inches in 10 years?).

1. #1 Garethti
2007/01/18

I’ll take Meltwater Pulse 1A-type rates of SLR (50mm per annum) sometime this century. The real bet’s about when it starts…. ;-)

[Ah. Sometime this century is a bit vague for a bet, though -W]

2. #2 Steve Bloom
2007/01/19

The foot in 20 years seems not unreasonable, but I’m not sure what sort of odds to put on it. Even? Of course, such a long wait takes all the fun out of it.

[Would you really consider even odds? How about 6 inches in 10 years? -W]

3. #3 Steve Bloom
2007/01/21

Looking into a bit more, I see that the high end of Stefan Rahmstorf’s recent synthesis effort was about five feet in the next century (probably what I was vaguely remembering), and given the “known unknowns” of ice sheet dynamics I would be prepared to stick with that. OTOH, it seems impossible that the rise would be anything like linear, so a foot in twenty years is out and six inches in ten years even more out. My semi-informed lay guess would be that something like three inches would be about the most one could expect in the next ten years. That’s probably still a little high, but I’d be willing to make an extremely nominal even odds bet on it.

[Ah well, 3″ is about 7.5 mm/yr so its rather unlikely. We can consider ourselves to have a nominal bet on it, but I doubt either of us will remember -W]

4. #4 Gareth
2007/01/22

OK. I’ll suggest “post 2050” and make a provision in my will. £10? I guess you’d offer 100-1 to my legatees…

The serious point is that whatever the perception of alarmism inherent in the wilder predictions, you do need to define a “sensible”* upper limit, particularly when considering infrastructure investment. If I were in the market for a seaside home, I think I might make sure that I didn’t buy on the beach. A 10 metre descent every morning is both bracing and healthy, if a little irksome in the evening.

* You obviously need to define “sensible” as well.

5. #5 James Annan
2007/01/22

Steve, 3 inches is a long way short of a foot or two. I thought you were the sort “intelligent lay person” who could look at a range of estimates from scientists and then claim that the high end was more likely :-)

2007/01/22

“You obviously need to define “sensible” as well.”

I guess that you’d mainly need to take into account the effect of a small rise on a storm surge – eg would a 10cm rise have a big effect on the outcome of an “average” swell, or “rare” swell etc.?

But other things to take into account are future affects on house prices – eg if a flat having less than 80 years leasehold remaining can lose value, what would an estimated lifetime of 80 years have on the value of a sea-side house you wish to sell?

7. #7 Steve Bloom
2007/01/22

James, I am indeed but a humble lay person, but now I see in yesterday’s Observer that a meter per century (more or less Stefan’s mid-point) has become canonical for this blog. :) But on the main point, how is 3″ in the next decade inconsistent with Alley’s remark? Is it unreasonable to assume a slow start to the process?

(On your other point, I think my response at Inkstain clarified things, but what I was trying to say is that “known unknowns” will tend to push the sensitivity range up.)

8. #8 Mike
2007/01/23

I suspect that “Entirely possible” means that current understanding can’t rule it out completely. But that doesn’t make quite as good a media scare story.

9. #9 Eli Rabett
2007/01/23

I think a lot of this revolves around the dichotomy between the rise to be observed by date x, the rise committed to (in the sense of there is no way of stopping it) by date y, and the ultimate rise z. There are three different shells and you have to be careful of which one you are turning over.

For example, in AIT, Gore is clearly speaking about z. Hansen talks about y in his PNAS papers and Wm is talking about x.