The above image from NOAA via The Oil Drum shows us that the temperature of the Eemian interglacial about 125,000 years ago was persistently above that of our times for several thousand years (oldest data is on the right). Hansen tells us that when the temperature was 1-2C higher than now during the Eemian the sea level was 4-6 meters higher. The frightening bit is that CO2 levels apparently did not go above 300ppm.
At 386ppm we should worry.
This is what a moulin in Greenland looks like.
James Hansen reports a field glaciologist saying, “the whole damned ice sheet is going to go down that hole!”
That image has become iconic.
A moulin looks like a waterfall, but it’s a hole down which meltwater falls to the bottom of the ice sheet where it lubricates the base of the ice sheet helping to destabilise it. Moulins also speed glacier flow. Diagrammatically they look like this.
The following image shows the increase in meltwater in the decade to 2002.
This one from Columbia University shows the ‘progress’ by 2005.
Note that the melt in 2005 advanced well above the 2000 meter line. This brings up another problem illustrated by the banner on this image (inferior in quality to the similar one further up, but it makes the point.)
The ice sheet, up to three kilometers thick, is losing altitude. Over the years this brings the surface down into warmer air where the melt increases.
The more meltwater, the more moulins. Here is a dramatic witness about moulins, ice-quakes, and glaciers from the Guardian last year:
Dr Corell, director of the global change programme at the Heinz Centre in Washington, … had flown over the Ilulissat glacier [said to have spawned the iceberg that sank the Titanic] and seen gigantic holes in it through which swirling masses of melt water were falling. “I first looked at this glacier in the 1960s and there were no holes. These so-called moulins, 10 to 15 metres across, have opened up all over the place. There are hundreds of them.”
This melt water was pouring through to the bottom of the glacier creating a lake 500 metres deep which was causing the glacier “to float on land. These melt-water rivers are lubricating the glacier, like applying oil to a surface and causing it to slide into the sea. It is causing a massive acceleration which could be catastrophic.”
The glacier is now moving at 15km a year into the sea although in surges it moves even faster. He measured one surge at 5km in 90 minutes – an extraordinary event.
He had a 40-year subjective view, but not all scientists doing short-term measurements are so gloomy.
Though how they can contemplate with equanimity an ice sheet half a mile thick and 50 miles from the sea moving 100 yards in a year while there is a net melt of 5 feet, I’m not sure.
Speaking of moving, the movement of the heavy ice sheet causes seismic activity termed ice-quakes. This histogram from the Earth Institute at Columbia University shows a disturbing trend in ‘ice-quakes’.
The pattern in Greenland, then, is one of increasing meltwater, faster ice flows in glaciers, thinning of the ice-sheet, more frequent “ice-quakes” indicating movement in the ice-sheet and increased net ice loss of ice volume as shown by satellite telemetry.
The internet abounds with stories of Greenland’s glaciers speeding up by two and three times in relatively short spaces of time. The bottom line, though, is whether the ice sheet is losing mass.
Here again stories are easy to find. The National Geographic reported in 2006 that the “rate of ice-mass loss … increased by 250 percent during a period spanning May 2004 to April 2006 relative to the period from April 2002 to April 2004.” A post at The Oil Drum draws attention to a comment at RealClimate indicating the following mass loss in cubic kilometers:
1996 -93
2000 -119
2005 -215
This was represented graphically at The Oil Drum as follows:
Hansen tells us that if the ice loss from Greenland and Antarctica doubles every decade, which is probably the worst case scenario but possible, 5 meters sea level rise will be the score by 2100. Hansen thinks that with 2-3C of warming we can expect the whole ice sheet to be bathed in summer meltwater. His best estimate is two meters of sea level rise by 2100, which will cause all manner of grief.
Turning to Antarctica, while it was cleared away by the IPCC as not a concern, it’s a worry still. According to Gavin Schmidt at RealClimate a recent paper shows that “the melting of the Greenlandic ice cap can only have caused a sea level rise of about 2 meters” during the Eemian 125kya. Most of the rest, 1-4 metres depending on which figures you use, is likely to have come from Antarctica.
Antarctica differs from Greenland in five main ways. First, it is higher latitude, colder and remote from land masses subject to more intense warming. Second, the ice is in contact with the sea around the whole perimeter. Third, the bedrock of West Antarctica is below sea level. Fourth, Antarctica has a lot more ice shelves. As floating ice they don’t increase sea level as such if they melt, but they buttress the ice sheet on land. Finally, topographically under the ice Greenland is shaped like a saucer, whereas the ice on Antarctica is more likely to slide if the buttressing ice shelves go and the rock under the ice sheet is appropriately lubricated.
The ice shelves can be seen in the following image:
This NASA image shows melt areas creeping inland.
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. One of the factors in Antarctica is that ice flows can move at different speeds, creating cracks which cause chunks of ice to crack off. This image gives a general view of where the ice is moving and how fast (purple is fastest).
Given that much of the bedrock of West Antarctica is below sea level, the above images show that this whole area is relatively vulnerable. Clearly, though, there are areas of concern around the perimeter of east Antarctica.
Once again the bottom line is net ice loss. A recent study found 196 gigatonnes loss of ice in 2006, compared with 112 in 1996.
West Antarctica has ice to raise the sea level about 5 metres and East Antarctica is worth about 57. Greenland is worth about 7.
One of the effects of the dramatic warming in the Arctic is that it will promote warming in the Greenland area. This is a map I made up from this NASA site showing 1990-2007 temperatures compared to 1880-1900 (grey means no data available).
It’s easy to see that Greenland is very much in the front line of global warming.
Climate Code Red citing research gives the “critical melt temperature”, whatever that means, of Greenland as 2.7C. They cite this as though they mean in context 2.7C above preindustrial, although their standard is to quote all temperatures referenced to the present temperature (this sort of thing drives me nuts). But local temperature rises in Greenland run at about 2.2 times the global. Also 2.7 is one estimate, I think Stern says 2-3C. However you cut the figures, bearing in mind the momentum in the system, (0.6C traditionally, but 2C according to Hansen) we are as good as there.
Although we can’t call a trend from the short periods of accelerated melting, what’s happening is a very good fit with what appears to be inevitable, given time. It’s looking very much like the Greenland ice sheet is in play and there are worrying signs relating to West Antarctica as well. East Antarctica is not exempt.
There is some hope, though. Greenland suffered a part melt 125kya and it turned around with nothing more than the relatively weak influence of orbital changes. Although Hansen says you can’t sling a rope around an ice sheet, I suspect that if we got CO2 levels down the whole thing would turn around quite nicely, given time, probably heaps of time.
Secondly, there is evidence that the interior of east Antarctica has been cooling.
Two reasons are suggested. First, Antarctica is very dry. Gore’s book says that precipitation is less than 25mm per annum. Warmer surrounding waters may increase precipitation. Second, the ozone hole, which is far from fixed, is thought to have tightened the circulation patterns over the South Pole.
Antarctica is more isolated now than it was when last ice-free 35-40mya. So the central mass may be somewhat resistant to melting under temperatures that prevailed then. We should recall, though, that around 3 million years ago when the temperature was 2-3 degrees higher than now the sea level was 25 meters higher, plus or minus 10. Mark Lynas in Six Degrees (2007) tells of a 1996 paper recording the discovery of fossil leaves from a stunted, ground hugging beech which grew just 500k from the South Pole at that time.
Indeed, at 386ppm we should worry.
Update: I’ve added an image of a topographic map of Antarctica after removing the ice sheet and accounting for both isostatic rebound and sea level rise. It’s from Wikipedia and is intended to show how Antarctica may have looked 35mya when ice free.
I assume that this one is without isostatic rebound.
Update 2: I’ve added a resized version of the second 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.
Update 3: Roger Jones’ comment on another thread and subsequent comments by Barry Brook are worth a look.
Interesting Brian, thanks.
David, it always good to get some feedback, so thanks.
Some of my colleagues say they read these posts, have a bit of a cry and then have a Bex and a lie down, in a manner of speaking.
This is the last of five on sea level change as such. I’m hoping to do three more on related subjects. One on declining ocean sinks and implications for targets. This brings up the issue of ocean acidity, where I’m less confident about the information, but we’ll see how we go.
Then one on extreme weather events, because heightened sea level makes them more dangerous.
Finally, a summary post.
Then I’ll be either going away on a planned trip, or I’ll attempt to rejoin the human race in some way and pretend that life is ‘normal’.
Thanks Brian. Very interesting and just a little scary. Puts all the political bickering, with regard to petrol pricing etc, into better context. How great would it be if we could see our pollies work together for the good of us all. (am I asking too much?)
No Debbieanne, you are not asking too much. I’ve been thinking dark thoughts about Brendan Nelson and the Opposition. Is there any way we can have him for treason or crimes against humanity?
Feel free to use any of this stuff to assail pollies. I’m hoping that the summary post will facilitate this.
Thank you Brian. Your posts on this issue have been outstanding. I’d like to add most of the media to the crimes against humanity charges, but in the end it’ll come down to each and every one of us.
Maybe someone should start a post about what sacrifices each one of us would be prepared to make because we’ve done most of the easy stuff, and soon we are all going to have to face some hard choices. Or maybe the choices will be forced upon us.
Brendan is an opportunist and he’s desperate. He probably never really cared much about climate change or the environment, and he knows that petrol prices and ETS scare campaign are his ticket to survival.
The guy who has really sold his soul is Greg Hunt. Climate change (AFAIK) is a lifetime passion for him, and its almost as sad to see him pushing Brendan’s populist nonsense, as it is to see Peter Garrett promoting voluntary energy labels for plasma TVs.
BTW, great post Brian, but didn’t you know the world stopped warming in 1998? And great to see you reading (and linking to) The Oil Drum.
Thanks for the posts Brian. Those moulins are pretty spectacular. Have you ever seen any subglacial maps of west Antarctica and Greenland that show depth, all the maps that i have seen have simply shown the shapes of the land masses above the water line.
This was so interesting, thank you for making the effort to share, clearly there’s some work involved.
Brian,
good post and summary.
For a feel on how moulins may operate in a land-based ice sheet, think of a karst (limestone) landscape. The moulins are equivalent to sinkholes. The landscape opens up along fractures between weak points as stresses caused by altered loads due to melting have an influence. Underground rivers link sinkholes. Then the landscape becomes canyoned with occasional mesas before breaking up completely. Except, with ice, it’s much faster, taking years instead of millions of years.
A grounded ice-sheet below sea level (e.g. West Antarctica) will behave somewhat differently, because of the possibility of it becoming afloat and melting from above and below. Breaking up in sections similar to recent ice sheet collapses (Larsen B) is the MO in that case.
Partial melting of Greenland is an option if we miss the melting threshold but can moderate subsequent warming:
Unfortunately the full article is only available to subscribers
Andrew Macintosh and Oliver Woldring have released what looks like a very good paper on climate carbon cycle feedbacks and their policy implications today. Needless to say, 60% by 2050 is a bit of a joke…
Thanks everyone.
Peter W I heard about that paper on the radio today so thanks for the link.
dylwah, I’ve seen both but unfortunately didn’t bookmark them and when I tried to find them again I couldn’t. The Greenland one was reconstructed by a blogger.
I have read recently that the middle of Greenland is about 300m below sea level, but is some of that is due to the weight of 3 kilometers of ice. Antarctica has 4 kilometers of ice, so there is plenty there.
Hey, I’ve just found one for Antarctica. Still can’t find one for Greenland.
200,000 years ago the first homo sapiens walked the earth. 58,000 years ago there was a land bridge between Tasmania and Australia and Australia still had it’s magafauna. The Persian Gulf reflooded 12,000 years ago, and last year the northern passage didn’t open for the first time ever, it opened for the first time since the vikings. And yes it looks very much as if Greenland is going to be green again.
Things are going to change, they always have. The crazy people are the ones who believed they wouldn’t, and I suspect the real crazy ones are the ones that believe we can stop it. Perhaps the monkeys that built freeways will survive, perhaps they won’t. Time will tell.
A third reason why central Antarctica is suspected to be cooling is because an increase in the speed of the circumpolar winds, which prevents penetration of warmer air from the mid-latitudes. This increase in wind speed is driven by two things: (1) loss of polar stratospheric ozone [another effect, other than the direct cooling Brian mentioned], and (2) [and this is potentially the MOST disturbing recent observation of accelerating global warming] a latitudinal expansion of the tropical zone weather systems (Hadley cells, Walker circulation etc.), which is pushing mid-westerly and circumpolar weather systems further polewards (north and south).
A recent meta-analysis and some comments on this can be found linked here:
http://www.aussmc.org/Tropics_expand.php
Regarding trees in Antarctica, a palaeobotanist colleague of mine at the University of Adelaide was one of the first to show clear fossil evidence of conifers (pines) growing along the Transantarctic Mountains during the mid-Pliocene about 3-2.5 million years ago.
http://palaios.sepmonline.org/cgi/content/abstract/11/4/389
At that time global temperatures were 2-3 degrees warming than present (a low-range projection for the 21st century). Sea levels were 25 m (give or take 10) higher than present – no prizes for guessing where most of that sea level contribution came from – Greenland, West Antarctica, thermal ocean expansion and a partial melt of East Antarctica.
Note that for Brian’s first slide, those temperatures are derived from polar ice core proxies (oxygen isotopes) and so are ~twice global temperatures. Globally averaged, the different between the depth of an ice and and a warm interglacial such as the Eemian was about 6C.
Here http://www.independent.co.uk/environment/climate-change/expanding-tropics-a-threat-to-millions-761326.html is the link to The Independent news story on the expansion of the tropics – Brian, perhaps you should do a story about this!
The implications Australian rainfall are particularly grim. This expansion is predicted by the current crop of Global Climate Models (GCMs), but they forecast a ~2 degree latitudinal expansion during the entire 21st century. Turns out, based on a analysis of a number of different meteorological features, that there has been closer to a 3 degree north and south expansion within just the last 30 years.
This tropical expansion is one of the principal drivers of the GCM-predicted decreased rainfall, of 10 to 40%, for southern Australia, western USA, southern Mediterranean Europe and South Africa. Unfortunately, it seems somewhat more likely now that tomorrow decided to make a house call today instead…
charles, if you can’t work out that there’s a relationship between CO2 levels and temperature with implications for sea level and that there has been something very unusual going on with CO2 and temperature in the last century or so, and that we have options in relation to CO2 emissions, then there’s nothing much I can do for you.
So the interesting information you contribute is simply irrelevant, as far as I can see.
Roger and Barry, special thanks for contributing your expertise to our little blog.
Barry, the study Lynas mentions on fossil plants in the Transantarctic Mountains is by Francis and Hill, the very one you link to.
Barry, at 14, I’ll take it on board. It’s something to worry about.
Today in the Fin Review there was a story of the enormous wheat plantings this year. I worry that it’s going to come to grief.
BTW I’ve added an update to the post showing this image of Antarctica, meant to show how it was 35mya with isostatic rebound when it was ice free, with adjustment for sea level. Not quite the same as now, but it indicates where the problem is with West Antarctica.
I’ve added a second update to the post showing a resized image of the topography of the subglacial bedrock of Antarctica in relation to the present sea level.
Hey this may be of interest: Greenland meltwater will take slow wave around globe. Short version – Florida is f*cked quicker than the rest of us.
That’s amazing, wilful. I’d say it isn’t good news for New York.
Today I heard a program on the Carteret Islands. Generally speaking the water is piling up a bit, or rather it is warming more and hence expanding more in the Western Pacific. They were suspecting El Nino, but amazingly that caused the water to go down considerably, from memory about 20cm. But they thought the El Nino might still be a problem, because of the effect it had on sediment transport.
I guess it goes to show how complicated things are.
Looks like we’re in for a reprieve. Both Arctic and Antarctic sea ice have expanded recently. Check out http://igloo.atmos.uiuc.edu/cgi-bin/test/print.sh?fm=07&fd=10&fy=2007&sm=07&sd=10&sy=2008 for latest Arctic sea ice. Looks similar to 10 years ago. Antarctic sea ice is at record highs since measurements began, see http://motls.blogspot.com/2007/09/antarctic-sea-ice-at-record-high.html (Someone is going to have to help me with internet links). I guess that can be expected from a 18-month worldwide cold spell.
How can Antarctica be cooling and yet melting at the same time. Or have I over looked some key point or fact in my haste?
Jack, the centre of Antarctica is cooling a bit, while the perimeter is warming. See the third last image in the post.
Dan, it’s my impression that what happens in winter is as may be, but what happens in summer is more significant. Also there have been constant reports on the BBC in the past day or so that the Wilkins ice shelf is hanging by a thread. So we’ll see how it all develops.
On the Arctic, it was generally expected that 2008 might pull back a bit from the big melt in 2007, just as 2006 was better than the record melt of 2005. But have a look at the third image in this post. That was a month ago.
Also the image in this article which I think was taken about a month later in the season seems to show a lot less ice in 2007 than the image you linked too. I think it’s a bit early to tell what the outcome for 2008 will be.
Meanwhile, in the corridors of power:
http://www.telegraph.co.uk/news/worldnews/2277298/President-George-Bush-%27Goodbye-from-the-world%27s-biggest-polluter%27.html?funny=not
This man has a red button on his desk.
Dan, here’s another item on the Wilkins ice shelf from The World Today. There was even a short article in the Courier Mail about it today.
What has the scientists scratching their heads is why this appears about to happen in the middle of winter. When the last Larsen ice shelf collapsed it was at the end of summer. The thought is that the warmer waters are chewing it up from underneath. This would highlight that what happens on the surface in winter is not the most important thing.
Katz, that’s gross!
Yet another article the Arctic melt. There is a link that shows how things are going.