The invisible modifier and another fine mess in the West Antarctic Ice Sheet collapse
There's a philosophical significance to the recent papers suggesting WAIS collapse is now unstoppable over the course of 200-900 years. The documentary video below depicting global climate change policy management since we became aware of the issue in 1896 gives the context:
Now we've really done it. Many of the other large-scale harms caused by climate change are reversible. On a human scale, the loss of life isn't, but this type of planetary modification takes it to a different level. I've been noncommittal on whether tipping-point arguments are convincing, but if these studies are correct, then we need to acknowledge that we've tipped into a fine mess.
As Eli discusses below, Andy Revkin completely misses this and instead makes what I call the "invisible modifier" argument that when somebody says X, the invisible modifier turns it into Y. This invisible modifier could be a shield, so when I say A and you point out that A is grossly exaggerated, I say that A only refers to certain situations I hadn't actually said it was limited to. Invisible modifier to the rescue! Here, Andy uses it as a sword:
Some headlines are completely overwrought — as with this NBC offering: “West Antarctic Ice Sheet’s Collapse Triggers Sea Level Warning.” This kind of coverage could be interpreted to mean there’s an imminent crisis. It’s hard to justify that conclusion given the core findings in the studies.Here, Andy says the invisible modifier added the words "of an Imminent Crisis" to the end of the headline. That modifier was so powerful it even covered up the article's first sentence, "Two teams of scientists say the long-feared collapse of the West Antarctic Ice Sheet has begun, kicking off what they say will be a centuries-long, 'unstoppable' process that could raise sea levels by as much as 15 feet."
Like the slippery slope and many other bad arguments, what makes it worse is that it is on occasion a valid argument - not everything is always stated, so there could be an unstated qualifier that could reasonably limit or unreasonably overextend an argument. Here, it's pretty clear that Revkin is wrong.
The key issue is the near-permanence and this tipping point demonstration of climate change.
Posts
14 comments:
In an e-mail string including Eric Steig (whose contribution was posted here earlier), Richard Alley of Penn State wrote this:
~~
Just to chime in as well… IPCC, or NAS/NRC, or other authoritative assessments, do prefer to use results shown by multiple models, from many groups, before making definitive statements. But, I think we would say that the most likely outcome now is that Ian is correct on the changes having started, even while calling for more work to raise confidence. And if we were Bayesian rather than Frequentist, we would start from that result. Furthermore, because Joughin et al are very clear that they have not simulated a worst-case scenario, nor necessarily have they come very close to doing so, it is worth remembering that the rapid changes once triggered may be notably faster than simulated, potentially relevant for reassurances about long time scales.
Reposting of R Alley's comment which Revkin posted.
"rapid changes once triggered may be notably faster than simulated, potentially relevant for reassurances about long time scales"
To date we have not ever been surprised by the speed at which sea ice can disappear. Therefore we don't have to worry about no silly old glaciers.
It's an ice sheet. The glaciers and ice shelves are just the corks to the bottle of carbonated water.
Go ahead, shake it some more, lol.
Let me reiterate, 'we' is 'you'.
So this has been validated, has it?
Yuurs, the philosophical thingyo, was wondering about that at P3. The first confirmation of a tipping point - that we've committed future generations to something this severe - is a. Thing. Of some sort.
While I'm here, I'll ask the same question I did there about the NYT article. It says: "scientists said the ice sheet was not melting because of warmer air temperatures, but rather because of the relatively warm water, which is naturally occurring, from the ocean depths"...
Naturally occurring? I seem to recall something about lots of heat going into the oceans. Why is the article saying it's naturally occurring?
I don't think Revkin is wrong - the issue he raises is an important one that should be discussed. I do think he is overly aggressive. The irrebersibility of the ice sheet collapse, and the centuries long time scale are both important issues that need to be communicated clearly. I remember my early impressions of sea level rise (from the 90s) were that multi-meter level rises were expected within a few decades. I'd suspect this impression was due to a combination of sensational headlines, and careless reading on my part.
I quite like the Jeff Masters headline of 'slow motion collapse'. And if I didn't know the detailed context, I'd probably interpret the NBC headline that Revkin singles out as a small ice sheet in west Antarctica has just collapsed.
In the comments at Revkin's blog he posts this:
Ian Joughin, the lead author of the Science paper, sent these valuable thoughts:
In defense of collapse, if I say "The collapse of the Roman Empire" you all pretty much understand what I mean and am talking about about a timescale similar to that for WAIS. And I think most members of the public would too. If collapse can't refer to extended periods such as decades to centuries, someone should contact Jared Diamond and ask him to change the title of his best seller.
And someone should also talk to the Astronomers "The collapse to a white dwarf takes place over tens of thousands of years, (Wiki page on gravitational collapse)".
....
The next blog post then discusses the consequences, starting with this quote from a paleontologist:
The extra sea level rise due to the collapse of West Antarctic ice masses will play out over several centuries. ...
When such changes are so slow, it’s hard for people to notice or even believe in them...
This is not the scenario Joughin et al. paints:
“All of our simulations show it will retreat at less than a millimeter of sea level rise per year for a couple of hundred years, and then, boom, it just starts to really go,” Joughin said.
Researchers did not model the more chaotic rapid collapse, but the remaining ice is expected to disappear within a few decades.
I'm not so sure "aggressive" quite covers it.
No guarantee it's 200 years away. Other glaciers in Greenland might go "boom" much sooner. Pretty hard to model catastrophic ice events. Is this a replay of the unformitarianism versus catastrophism debate among geologists? Sea level rise might become a series of step increases as we suddenly lose various glaciers.
Bill W.
Lest anyone has forgotten how ice melt can catch even the best professionals off-guard, here's a reminder.
And on tipping points... In many situations, whether biological, geological, chemical or physical, tipping points are described by a sigmoid curve. Think titration. And recall that not much seems to hapen for a while, and then there's a rush toward a new equilibrium.
We've primed the planet for many tipping points, some recognised, many not. Many have the capacity to synergise, mutually or commensally. The collapse of WA ice might take several centuries amd perhaps even a good handful of them, but that doesn't mean that there won't be a concurrent broader, faster collapse of other systems.
Pedantic semanticists need to stand aside and let the real message find its way out.
It's not a nice message.
There is a "aquifer" the size of Ireland sitting on top of the ice and in the firn. ( http://www.nasa.gov/content/goddard/enormous-aquifer-discovered-under-greenland-ice-sheet/#.U3RVdvldWtI )
Water on top of ice is not stable. When that water goes, it will take the firn with it. It will make quite a splash. It is only 0.4 mm sle but it is a long fall to sea level. There are other things out there to think about.
However, Anders Levermann agrees that there are mechanisms by which the ice can collapse much faster than the time frames discussed in the paper. The question of the time frame is not settled.
As we watch Greenland melt & aquifers are pumped dry it might be worth asking if rising sea levels don't act as an accelerant in the Antarctic.
Terry
Terry
Of course they do. Ice floats, and the WAIS is a marine ice sheet. All significant increase in MSL, whether primarily driven by the GrIS or the WAIS or both will float the glaciers draining the WAIS off their grounding lines and so increase their flow rates. Water will also be able to penetrated ever-further beneath the WAIS, which is on a retrograde grounding slope, so destabilising the whole ice sheet still further.
Positive feedback if there ever was.
The name is Bond, Gerard Bond.
Dan: natural change? maybe not
http://www.realclimate.org/index.php/archives/2014/04/unforced-varaitions-apr-2014/comment-page-6/#comment-529982
Post a Comment