Al Gore talked about some scary stuff with respect to sea level rise, but didn’t in fact put a time limit on it. James Hansen has suggested that multimetre sea level rise by 2100 is highly probable. At least twice in recent times he has nominated two metres by 2100. In the Huffington Post he said:
West Antarctic and Greenland ice sheets are vulnerable to even small additional warming. These two-mile-thick behemoths respond slowly at first, but if disintegration gets well under way, it will become unstoppable. Debate among scientists is only about how much sea level would rise by a given date. In my opinion, if emissions follow a business-as-usual scenario, sea level rise of at least two meters is likely within a century. (Emphasis added)
He said the same thing in his 2008 testimony to Congress.
Now scientists at Colorado, Montana and Scripps (Pfeffer et al) have suggested that two metres, while possible, is extremely unlikely. 80 centimetres is “more plausible”. More than 2 metres would be physically impossible.
There have been reports of this research all over the world, but the simplest explanation I’ve found is (would you believe) from the Zimbabwe Star:
A new Colorado University study has pegged rise in sea levels to six feet by 2100, rather than the 20 feet feared by some scientists.
Calculations were made using conservative, medium and extreme glaciological assumptions for sea rise expected from Greenland, Antarctica and smaller glaciers, the three primary contributors to sea rise. [Actually they include a fourth - thermal expansion - which at 30cm is the largest factor in their preferred scenario.]
The survey team concluded the most plausible scenario, when factoring in thermal expansion due to warming waters, will lead to a total sea level rise of roughly three to to six feet by 2100.
The team found that some of the very large predictions of sea level rise are unlikely, because there is simply no way to move the ice or the water into the ocean that quickly.
They began the study by postulating future sea level rise at about two metres by 2100 produced only by Greenland.
For Greenland alone to raise sea level by two metres by 2100, they said, all of the outlet glaciers involved would need to move more than three times faster than the fastest outlet glaciers ever observed, or more than 70 times faster than they presently move.
The study concluded the outlet glaciers would have to start moving that fast today, not 10 years from now.
Pfeffer et al do a pretty good job at analysing the ice dynamics of Greenland. Essentially their contention is that given the bedrock topography, which is like a saucer, ice that melts or is destabilised by moulins needs to pass through gateways where it comes in contact with the sea. The problem is illustrated as follows:
Greenland glacier gates
I gather the marine gates, marked in dark green, are the important ones.
While we’re at it here is an image showing the shape of the rock as such:
Rock under Greenland ice
This is the corresponding image loaded with ice:
Greenland loaded with ice
Those images are from here.
You can also see the bare bedrock image spinning.
Pfeffer et al begin by calculating the glacier speeded etc you’d need for 2m and 5m from Greenland alone. If we assume that there would be a corresponding melt in Antarctica, which is reasonable, and taking into account the the other main sources – thermal expansion and other glaciers and ice caps (GIC) – we’d be looking at 5m and perhaps 11m. No-one is seriously suggesting sea level rise of this kind by 2100.
Then they work out three scenarios, two low at about 80cm and one high at 2m. The second low one makes most sense. They simply take “presently observed rates of change” and project them forward. This gives the following values:
Greenland – 16.5cm
Antarctica – 12.8cm
GIC – 24cm
Thermal expansion – 30cm
Total – 83.3cm
This is less than the midpoint of the range (50cm to 140cm) Rahmstorf came up with when he did a similar linear projection of historic trends.
Nowhere do they give their assumptions about how much warming there is going to be. It’s a fair bet that they are taking IPCC estimates of a midpoint of 3C with BAU (business as usual).
But when we looked at Hansen et al we found that he believes that the temperature increase for doubling CO2 (about 550ppm) will be 6C when long-term feedbacks are taken into account, such as the loss of albedo as ice melts. Certainly his ideas would seem to explain what is happening in the real world, especially in the Arctic.
The problem is that if you get to 6C you’ll almost certainly get more, because along the way you’ll trigger various tipping points, such as the release of methane clathrates from the sea, methane from land-based bogs, destruction of the Amazon etc.
Their high scenario is divides like this:
Greenland – 53.8cm
Antarctica – 61.9cm
GIC – 55.1cm
Thermal expansion – 30cm
Total – 200.8cm
I understand that 55.1cm for GIC implies that all glaciers and ice caps other than those in the ice sheets will melt completely by 2100. I believe this is plausible and likely. That already gives us 85cm with thermal expansion. Two metres doesn’t seem a big stretch.
Pfeffer et al point out that little is known about the dynamics of ice movement in Antarctica and GIC, but they seem to assume that they are constrained in a manner similar to Greenland. But we know that Antarctica is very different.
Again they set up straw men by pointing out that while the Pine Island/Thwaites Glacier area in West Antarctica contains enough ice to push up sea levels 1.5m this would require the ice discharge to increase from 2km/year at present to 53.6km/yr.
Pfeffer et al also assume that the vast Ross and Filchner-Ronne ice sheets will last the century. Yet the Kiwis think that the Ross ice shelf has “collapsed in the past and had probably done so suddenly.” If it does then the melting of Antarctica could proceed much more rapidly.
As we saw in a post Greenland and Antarctica a lot of Antarctica is below sea level and the ice is in contact with the sea around the entire continent.
The ice shelves can be seen in the following image:
Antarctica ice shelves
This NASA image shows melt areas creeping inland.
NASA Antarctica melt
Particularly concerning is the matching of melting with the ice shelves. These shelves are being attacked from meltwater above and warmer ocean water from below.
This is a topographic map of Antarctica bedrock. I gather that it shows the levels in terms of current sea levels. The line between blue and green is zero. Purple is -5-10,000 feet. Note that parts of east Antarctica are also shown as being below sea level.
Antarctic bedrock
My feeling is that the Pfeffer et al make a legitimate point about constraints on melting of Greenland during the next century. If the blow torch of heating is applied, however, their top estimate of about 54cm by 2100 could be exceeded.
The bigger uncertainty applies to Antarctica, which, once it ‘tips’ or is seriously in play, could initially melt quite fast, up to a point. That point may be defined by what happened about 3 million years ago, when total sea level rose by about 25 metres (plus or minus 10) with temperatures 2-3C above now and CO2 levels much the same as now. At that point, given the elevation of the ice sheet on East Antarctica, its then separation from the sea, it’s isolation and micro-climate, there could be some stability in the face of further temperature rise of a degree or two.
It seems clear that if we do nothing about greenhouse gases then the 22nd century will be very ugly in terms of sea level change. The question is how rapidly will things proceed this century. In this comment climate scientist Roger Jones after studying the literature on Greenland for three weeks said that while it seems that Greenland has tipped “we should get at least one more generation out of shorefront properties on most unprotected coastal dunes.”
After that there would be no guarantees.
Prof Barry Brook’s comments at 23 and 24 on the same thread are worth noting beginning with:
my view, shared by many colleagues, is that there is already large and rapidly accumulating body of empirical and direct observational evidence for accelerated melting of the Greenland and west Antarctic ice sheets, occurring now.
He also said on this thread:
425-450 ppm CO2 does not necessarily guarantee an ice free world. It will almost certainly wipe out the Greenland Ice Sheet (GIS) and West Antarctica Ice Sheet (WAIS) at some future point (I’d bet sooner rather than later – anywhere between a few decades to a few centuries and we are likely to be committed to this already at 385 ppm). But not necessarily the East Antarctic Ice Sheet (EAIS), or at least not all of it.
My feeling is that sea level rise is going to turn non-linear at some point and that point could easily be before the century is out. I’d tentatively suggest that Hansen’s notion of two metres by 2100 is more likely than 80cm which seems to me the minimum.
There were other reports of the research at:
There are posts at:
The Netherlands are planning their future:
Sea levels are expected to rise by over a metre before the year 2100, and up to four metres in 200 years time.
If memory serves, I think they settled on an 80cm to 1.3m forecast for 2100 (from the long comments thread at RealClimate.)
This is the last in a series I’ve done on sea level change:
Trouble at the top of the world
Scientific caution or climate change politics? the IPCC and sea level change
Sea level rise: some real world implications
Greenland, Antarctica and sea level change
Peterc collected some good stuff at Greenlivingpedia
If I were approaching the series the one on “Sea level rise: some real world implications” would be a good place to start.
On the local scene this 7.30 Report item has more than passing relevance:
Victoria’s Civil and Administrative Tribunal have moved to prevent the building on six blocks of land on the state’s Gippsland coast, which has sent a shock wave of uncertainty through local councils across the country. The tribunal overturned planning permission for the six blocks in part because of the threat of flooding from climate change.
Finally here is the link to an interactive flood map so you can check what could happen anywhere you are likey to buy real estate.
Great post, Brian. Thanks for much for all this clear-headed, lucid analysis and explanation you’ve been doing, I really appreciate it, though it depresses the hell out of me.
Thanks, Brian. That’s a pretty impressive post. There are so many things that I would never even think to consider (like the rate at which glaciers can move given the topography they face). I hope there are some smart people out there thinking about this stuff.
Excellent but worrying post Brian. Minor editorial quibble… “given the elevation of the ice sheet on East Antarctica, it’s then separation from the sea, it’s isolation and micro-climate, there could be…” your apostrophes in “it’s” don’t belong there, unless you mean “it is” rather than the possessive of “it”.
Excellent post Brian, congratulations.
Has any-one yet performed a study to show at what point the positive feedback from the liberation of Methane from the Methane Hydrate (Clathrate) deposits starts to become significant?
It is also worth noting that the melt rate from large glaciers can be astonishingly fast. I remember reading reports of a perched lake on a glacier formation that totally destroyed the formation within weeks. There is an interesting report here : http://www.st-andrews.ac.uk/~dib2/research/ngozumpa.htm
Huggy
Well, thank Gaia!
No need to relocate the jetty or build a new sae wall along the beach.
One problem with the 2100 timeline is that we might get a snapshot of where sea levels could be then, but where are they heading to?
Deeply concerning – thanks for doing the research Brian.
Reassuring to learn the science is so accurate – all based on measurable data with accurate modelling that fits past data. . . Not!!!
And we are going to hobble our economy based onthis type of uncertainty combined with the uncertainties of ever getting a global co-operative arrangement in place.
This is economic vandalism at best and madness at worst.
Thanks for the informative post, Brian.
However this debate plays out, I don’t think it alters the case for strong action much.
The complete devastation of land-based ecosystems, the elimination of coral reefs, the disruption of economically vital rainfall patterns, and so on is quite sufficient to justify massive action.
Furthermore, of course, even a one metre sea level rise is potentially devastating to lots of low-lying areas.
I suppose this is trivial in the wider context of the post, but I actually know several people who moved up to Armidale to live because its high up on the Northern Tablelands and protected by the gorges from rising sea levels.
Sorry Razor, which economy hobbling/vandalism are you alluding to? News to me…
The economic vandals are those sitting on their hands; and those who expect the global public to pay the cost of their free emissions.
Major emitters who dont pay their way are therefore welfare bludgers. Why are some sections of the right so afraid of economic innovation? Dirty industry is so retro dude.
Hal9000, thanks for sorting the apostrophe. Fixed now along with another error you didn’t mention. At my age there are a few standard errors I’m prone to and I don’t seem to be capable of learning the correct automatic response.
Huggybunny, I recently read an article saying there was twice as much methane in the bogs than previously thought. Didn’t bookmark it. Methane levels have been prety stable recently. This article suggests that there has been an uptick and wetlands are thought to be the problem. If so we could starting to get into trouble as of now.
As to clathrates under the sea, I don’t think anyone knows, but generally that’s the concern with the 2C guardrail. Remembering that Hansen says the guard rail should be 1.7C and he reckons we’ve got 2C in the pipeline (ie about 0.7 plus 2C) whereas the standard line is that he have 0.8C now and 0.5C in the pipeline. Time to get serious.
Mark Lynas in Six Degrees puts the methane clathrates problem a bit further up the scale, something about 4C plus above now. That’s going on the best research when he wrote the book late in 2006.
Razor, what Robert said.
On the thread at RealClimate they were asking seriously what the best advise would be if you were renewing low-lying infrastructure, given risk and a 50 year life-time of the infrastructure. The answer seemed to be that you’d count on a metre by 2050 or else you were irresponsible and certifiable.
The Dutch must (and I read, are) contemplating scenarios where they might have to abandon part of the country. I wonder about the Coorong, which is already half a metre below the sea now and has been unnaturally turned into a freshwater system in the lower lakes. I can’t see us ever getting ‘sustainable’ environmental flows since the system, I understand, started to deteriorate when we first took water out of it in the 19th century.
Long as it rises high enough to drown Ackerman,Bolt,Blair ect
Brian, atmospheric methane rose by 1/2% in 2007 after remaining steady for the previous 10 years. There is accumulating evidence that significant tundra melt is underway now. I also read an article, that I did not mark, claiming Skandanavian scientists have measured increasing levels of methane in Arctic coastal waters. If this is confirmed it may be that shallow coastal waters have warmed sufficiently to destabilise seabed clathrates with some consequential release of methane.
Do you know if methane released from tundra and clathrates will have significant or total decay of the isotope carbon 14 and can therefore be distinguished from methane released in agriculture and landclearing?
wilful, I think the best answer is the paleoclimate record, which from Hansen’s stuff I set out in this post as follows:
The last one is problematic, because it refers to a situation about 35mya, when India hadn’t smacked into Asia, hence the Himalayas weren’t there, nor were the Andes, the Americas hadn’t joined, Antarctica was less isolated, the ocean currents were bound to be different and even the shape of the ocean basins would have been different. The second last, however, refers to a time 3mya when things were pretty much as they are now.
Even if the ice sheets take 6000 years to melt, a figure that has been mentioned, that still gives an average of 1.25m per century. The effect of even this leisurely melt would be that you never have stable coastlines, and once the golden sands disappear they won’t reappear until there is greater stability.
Another way of looking at it is that if all the ice goes with a 6C rise, which it almost surely would, that gives you an average commitment of about 13m for every 1C. Remember during the last glacial maximum when the temp was about 6C lower than now you had a sea level 120m lower.
So the commitment involved in even small temperature changes is likely to be quite large, the main question is how long it takes to come to be. We need to find a way back to the paradise of the Holocene or what’s left of it.
Also many thanks for this and your previous research – riveting reads to say the least!
Great post, Brian, as have been all your others on this fundamentally important aspect of our planet’s future.
If “perception managers” world-wide could galvanise eathlings into fighting a Global War on Greenhouse Gases we might stand a chance of preventing some of the apocalytic consequences of rising sea-levels. Unfortunately, such initiatives compromise Big Carbon’s bottom line, therefore the corporate psychopaths who dictate BC’s policy are incapable of considering them.
Meantime, as our orb twirls effortlessly upon its axis, each day that “nothing is being done” draws us closer to the truth.
On the upside, at least there’s a place in cyberspace where can bone-up on our pending downfall:)
Great post. I note the statement “More than 2 metres would be physically impossible.” but don’t see anything to back it up. Why is it physically impossible?
The unknown in all of this is the performance of the methyl hydrates tucked away in many places around the sea floor and in permafrost.
BilB, it is a really scary scenario if they start to go off. It’s what they mean by “runaway” warming.
Steve D I think it has some force, especially in Greenland. Apparently the ice dynamics far outweigh the ‘surface mass balance’ thing, which is the difference between straight melting and snow precipitation. But if the heat’s really on you’d expect the meltwater to find a way. It’s just that it would need a hell of a lot of heat to make a big difference in a short time. I think they’ve got a reasonable handle on that one for Greenland, but are probably on the low side because of underestimating the amount of warming.
Good update Brian. The latest information from NASA indicates that sea ice at the Artic Arctic sea ice at second-lowest level on record. [link]
Brian, it’s a pity the flood map google maps hack only goes to 16 metres!
I hope and anticipate that even us humans will over a full century or more be able to stabilise atmospheric carbon at a satisfactory level below the previous maxima – even if all the tundra methane belches out, it’s not very persistent.
Steve D, I should leave it to Brian to explain, but my take away understanding was that the glaciers haven’t ever been known to move remotely fast enough for enough water to be carried to the ocean. This constraint is probably in large part inherent in the geography, the fact that Greenland has a ring of mountains, so there’s a big lens of ice sitting in the middle that’s not keen to just slide off anywhere.
Which is a good thing.
wilful, that’s the story as I understand it. Where you have ice sitting on rock below sea level in contact with the ocean, as you do pretty much all the way around Antarctica (with ice shelves over the sea in many places, you have the potential for things to move quickly when they start to go.
Here’s a post card from the deep north. Asheville’s temperature above Atlanta’s by 2099, sea level rise certain, hurricanes and wildfires maybe.
Here’s another worrier.
Thanks for the thanks, everyone. I’m off on the first decent holiday since 1999. I’ll be back blogging maybe by about November.
I’d like to acknowledge Peter Wood’s help and thank him in preparing the post.
Seeya.