Steve Bloom points out on a thread I had, oddly, hoped would be about Benin, that Tom Fuller is in Fuller bloom over at WUWT(*), accusing me again of being an alarmist, when I am merely alarmed about the state of the world (as described by Schellnhuber and Rockstrom and Foley). I truly wish I weren’t. I truly wish those guys were wrong. I truly wish I were wrong. But Fuller is not pulling together a convincing story, even though he seems to think he is.
Like Fuller, I am eager to find evidence for the incorrectness of my views, but unlike Fuller, I have a more deeply elaborated understanding, and consequently am a bit more skeptical and harder to convince of alternative hypotheses.
The present kerfuffle comes down, apparently, to Fuller’s claims about the Antarctic ice balance. Since I know or am at one degree of separation of some of the more prominent and talented researchers in the field of the mass balance of the great ice sheets, it reasonably falls to me to follow up and try to tell the whole story.
Before I look into it any further, let me state what my current understanding is. We can test out whether it is correct, but this is where I start.
The balance of evidence in mt’s brain
as of early September 2010,
on the subject of
THE MASS BALANCE OF THE ICE SHEETS
1) First of all, the equilibrium response to a 3 C warming is enormous. If we hit the (approximately known and likely by now unavoidable) 3 C threshhold, and at that point civilization has no more capacity to think in the long term as we do today, we are looking at sea level rise in the tens of meters. This means Greenland will substantially be melted down to the rock, the WAIS (**) will totally disappear, and a substantial fringe of
West East Antarctica will probably also be bare. The primary evidence is the geological evidence of seas that deep in the previous interglacial approximately 100kA ago.
2) It is considered nearly certain that the ice sheets will NOT respond quickly enough for the tens of meters of sea level rise which we would eventually expect with a 3 C rise to happen in this century (whew!) or even this millennium. But we would expect that level eventually if CO2 stays elevated high above quaternary (the past 2,000,000 years) values.
3) Rather than having a single time constant, though, the disintegration of ice sheets has recently been determined to be dynamically complex and operating on numerous time scales.
(Understanding the concept of time scales is key to understanding paleoclimate and clymate dynamics. As an example common everyday occurrence in some places I used to live is frozen puddles. Cold climate folk know that a puddle exposed to cold develops a film of ice first, and eventually freezes all the way through. The amount of time for it to gain or lose the thin film of ice at the top is much shorter than the time it takes to freeze through. Whether you are discussing whether the ice is superficial (say because you care about reflected light) or frozen solid (say, for traffic safety) determines a time scale of interest when you look at the weather.)
4) An ice sheet is in mechanical balance between large scale gravitational forces causing it to splay out and various small scale stresses and strains causing the ice to “like to” stay put.
5) On large physical scales, ice is a very viscous fluid, whose viscosity is sensitive to temperature. So different parts of the ice sheet flow at different rates. At the weakest points in the geometry, outlet glaciers form, which amount to areas where there is a steady flow of ice into the sea, which is where icebergs form.
(Icebergs are very different from sea ice.)
6) In a stable climate, the glaciers and the accretion of ice on top of the ice sheets are in rough balance. However, we know that the behavior of individual glaciers can be episodic, and important ones can grind to a complete halt, or conversely, speed up a great deal.
7) Imagine a huge mound of frozen grape jelly on a picnic table in the sun on a hot Texas afternoon. It will take a long time for the jelly to turn completely runny, though we know that will be its ultimate fate. Most of the jelly is a foot thick, but near the edges of the table it slopes off steeply. A tiny bit of the edge of the table is visible.
We know it will eventually run off the table, but consider how it might starts off. As the jelly warms up, it gets a little softer, and it can no longer sustain the steep slope. So it starts to spread. And the bits of spread that fall off the edge of the table no longer offer their viscosity to help hold up the rest of the pile.
The bits that fall off the table are like icebergs.
Near term sea level rise is about the fact that increasing temperature causes a gravitational instability at the steep edges. As long as the temperature increases, the edge of the ice sheets gets further into disequilibrium, and the ice sheet will retreat in much the same way as a beach retreats under rising sea level, where a small change in forcing yields a large response because the system needs to find a new physical slope.
8) It is also the case that the tops of the ice sheets, as they warm and hence receive more moisture, will be accreting. It will take a very long time before that mechanical signal becomes significant at the edges where the action is. Meanwhile, the tops of the ice sheets can somewhat mitigate sea level rise. The tops of the ice sheets constitute a true mitigating feedback to sea level rise, and in the short run this effect may dominate.
9) Both physical reasoning and paleoclimate evidence indicate that warming ice sheets do shrink, though. You were expecting, maybe, the Easter Bunny? So in the long run that effect is swamped by the shrinking edges, which makes sense in a simple model because the size of the accreting area shrinks.
10) A fellow named Christian Schoof appears to have worked out the mechanism for abrupt sea level rise such as the 14 kA event when sea level rose some 15 meters in 400 years. The mechanism has to do with ice sheets that have compressed the land the lie on enough that their bases are below sea level. Only certain geometric configurations of the outlets of such ice sheets are possible. If an ice sheet melts back or surges forward from one of these configurations, it is likely to reconfigure rapidly. There is only one such conditionally configuration on a large scale on earth at present, in the Amundsen Bay off the West Antarctic Ice sheet. If it were to retreat behind a certain ridge, it would become mechanically unstable, and a process would begin whereby it would eventually destabilize an ice basin large enough to cause an abrupt sea level rise of approximately 2 m.
11) The mass balance of Antarctica as a whole swamps the events in this area now, so the GRACE instrument may not pick them up. But nobody knows how quickly the destabilization will occur once the ice sheet lets go of its sill in the Amundsen embayment, which as I understand it, it already has. Once it starts, a one-time and abrupt sea level rise of about 2 or 3 meters in a few decades is plausible.
12) As for the Antarctic ice balance itself, I was coincidentally just looking at this picture in the Copenhagen Diagnosis
Here we see various estimates of the Antarctic mass balance over the past fifteen years. This is strongly suggestive of a significant change over that period.
Here, by the way, are comparable estimates for the Greenland mass balance:
13) A press release
just yesterday (!) amounted to a major correction to GRACE estimates of mass flux. This is apparently a correction for isostatic rebound. It is good news because it means our worst fears that might be gleaned form the above graphs may need reconsideration.
Based on this principle, previous estimates for the Greenland ice cap calculated that the ice was melting at a rate of 230 gigatonnes a year (i.e. 230,000 billion kg). That would result in an average rise in global sea levels of around 0.75 mm a year. For West Antarctica, the estimate was 132 gigatonnes a year. However, it now turns out that these results were not properly corrected for glacial isostatic adjustment, the phenomenon that the Earth’s crust rebounds as a result of the melting of the massive ice caps from the last major Ice Age around 20,000 years ago. These movements of the Earth’s crust have to be incorporated in the calculations, since these vertical movements change the Earth’s mass distribution and therefore also have an influence on the gravitational field.
The corrected figures are reported in a multi-author paper in the Nature Geoscience by Wu et al
. Quoth Wu:
According to our estimates, mass losses between 2002 and 2008 in Greenland, Alaska/Yukon and West Antarctica are 104±23, 101±23 and 64±32 Gt yr−1, respectively. Our estimates of glacial isostatic adjustment indicate a large geocentre velocity of −0.72±0.06 mm yr−1 in the polar direction. We conclude that a significant revision of the present estimates of glacial isostatic adjustments and land–ocean water exchange is required.
This is a significant correction, but it nevertheless remains the case that the mass flux is clearly negative from all major ice sources. Of course, there’s little reason to expect that this won’t eventually be the case. The question at hand is when, and the answer is already, but the GRACE satellites may be weighing in on the low side for the next question, which is how much.
14) There is a geoengineering project
called ice911 which I believe is worth considering that may fix the ice sheet problem.
(*) – WUWT is jargon on both sides of the climo-blogo-fence for “Watts Up With That
“, a blog of the sort that one refers to with a “nofollow
“. Watts has articles of varying degrees of sophistication, with the common thread that most of them are deeply confused. This does not mean everything said on WUWT is false. It means that all points of view are welcome
, which is to say, scientifically informed opinion is vastly outnumbered and openly mocked
. Watts provides a real service by providing a window into what people actually are thinking. How our society sunk to such a gnarled tangle that politically significant numbers of nonscientists see scientists this way is a subject I take up often, but not this time. Suffice it to say that articles on WUWT are often a horrifying mashup of information and disinformation, and that most readers have no serious basis to tell one from the other.
(**) – WAIS: West Antarctic Ice Sheet
ABOUT FULLER’S WUWT PIECE
“It is hard to understand many of those who are convinced that climate change will destroy civilization.”
That is a near-empty class. I consider myself among those who hope that climate change will not destroy civilization, and choose to act on that basis.
And according to some scientists working with GRACE measurements, Antarctica is losing ice. Not just the Western Antarctic Ice Sheet, which has been predicted to melt and succumb to mechanical pressure since the 1930s, but also the vastly larger ice sheet covering East Antarctica.
And sure enough, the ‘apocaholics’ are all over this, using it to reinforce their unrelenting drumbeat of doom-laden predictions of disastrous sea level rises.
But this is actually quite strange. According to climate change theory, ice should be increasing in Antarctica–the (very slight) increase in temperatures and the natural increase in precipitation should result in more snow over Antarctica which gets compressed into higher levels of ice. The same phenomenon is both predicted and observed in Greenland, by the way.
Both phenomena exist. At issue is which one wins. In the end, of course, ice sheets do shrink when the planet warms very much.
“Instead of using this as proof of global warming”
huh??? Sorry, what does that even mean?
” Because this is observed data working against the principles of their theory”
uh, nope, remember, there is a tradeoff, one which Fuller actually described himself
“But they cannot pass up the chance for a quick and easy headline that reinforces the ‘all disaster, only disaster, 24 hours a day’ routine.”
“Certainly all measurements before GRACE showed increasing ice in Antarctica, as they do today.”
There’s Fuller’s hat, providing us with anti-information again.
“My guess (I’m not a scientist and do not claim to know) is that there are still a few bugs to work out in how they are doing this.”
This turns out to be quite true and an amazingly well-timed guess.
“So the paper referred to by scare artists like Michael Tobis of Only In It For The Gold “
a – I am not a “scare artist”
b – It was Fuller who raised this paper
“says the Eastern Antarctic has lost 57 billion tons a year–plus or minus 52 billion tons.”
I only said that – 57 +/- 52 was a decrease. I do not know to which paper Fuller refers, and can’t seem to track down the original where he raises it. Fuller’s name-calling is one thing, to claim that I raised some paper in the conversation after he himself brought the figures to the table is something else. (I looked all over the place and can’t spot the conversation where this even came up, but I’m pretty sure the numbers came from Fuller and completely sure I didn’t come up with them.)
Not all measurements of ice mass balance are via GRACE, as is obvious from the long record of Greenland estimates. John Cook has a nice piece on this on Skeptical Science
It is one thing for Fuller to get the science wrong. On quantitative arguments requiring a little subtlety, one assumes he knows no better. But he is here making misleading statements on events of which he was a part. This can’t be written off just as intellectual hubris.
And then a repeat of the claim that seems to me totally at odds with the facts:
Other measurements, consistent with climate theory, have consistently shown the Antarctic gaining, not losing ice.
No. That is wrong. Say it twice and it’s still wrong.
Fuller seems to believe in making up facts to tell a convenient story. I don’t think this constitutes helping.