0 Lake Erie Ice

My friends at the Great Lakes Environmental Research Lab sent me word of their nice video of ice on Lake Erie. There was an unusually long cloud-free (or at least little cloud) period, so you can actually see some ice and its motion.

http://www.youtube.com/watch?v=IwW56v1Jt0U for the video.

Something for you to look at while I'm off-net for a few days.

When I'm back on line, I'll be answering some of the questions that are still outstanding. New questions and comments can still come in, just be aware that the moderation delay will be longer than usual. questions here. I'll also be looking in to adding a widget that will let you see the most recent comments. Since the blog is conversational, if a slow conversation, I do take them as an important part of what goes on here. (Or you can subscribe to the comment feed, icon over on the right hand column.)

Detail: Lake Erie Ice

0 Antarctic Snow and Ice

The Antarctic has long been a favorite area of mine, going back to graduate school days.  This particular note, however, is prompted by a question over in the question place -- regarding Antarctic mass balance and snow.

The question at hand turns on just what is going on with Antarctic mass balance.  The apparent 'conflict' is between a study showing a recent decline in snow melt, and other studies that Antarctic ice mass is decreasing.  This is a particularly simple conflict to resolve, so I'll note that it really is taken as a serious conflict (per the questioner's link) over at WUWT (haven't we heard that name recently?)

The simple reality that the authors of the snowmelt paper are perfectly aware of, but WUWT ignored, is that there is more than one way for the Antarctic to lose mass.  I grant that melting the snow is the most obvious one.  But, when you're dealing with a continent as incredibly dry as the Antarctic is (the driest, and probably largest, desert in the world), you have to pay attention to more subtle processes.  One of them is not at all subtle -- huge icebergs break off of the Antarctic from time to time.  In these cases, you're talking about chunks of ice several hundred meters (call it 1000 feet for simplicity if you're non-metric) thick, and 50-100 km (30-60 miles) on a side.  Chunks large enough to be the size of entire US states and some countries.  (I have an ancient listing of some iceberg sizes and country, state, lake sizes for your comparisons -- additions welcome.)  There's also the very subtle process of evaporation straight from the surface of the ice sheet (sublimation) into the atmosphere.  And there's the not subtle but easy to forget about fact that Antarctica has ice shelves -- ice floating on the ocean that's fed by the continental (sitting on land) ice sheet -- and the bottoms of those ice shelves can and do melt.

Finally, there is the rather bizarre fact that ice is not a solid.  Once you build up to having an ice sheet, the pressure of the ice above a point near the ground is so enormous that the ice flows.  Ok, it's a really, really, thick fluid (think very cold molasses).  But it flows.  This means that the ice sheet move mass out to the edges -- out to the ice shelves where there can be snow melt, ice evaporation, or ice shelf melting, or massive icebergs can break off.

So, just on a fairly cursory consideration -- there's more than one way to skin a cat, or, rather, there's more than one way for an ice sheet to lose mass -- we already know there's a problem with the WUWT article.  In the science, no real conflict.  More below the fold.
The scientific papers involved are ...

First -- a hearty thank you to Jesus for providing the links!  As you can see from my link policy I appreciate substantive links being provided.  That's really the only way I can be sure that I know what science you mean, and only way for you to show what good science (or bad, alas) it is that you've found.  And not only me, since I'm only one reader of the blog, but all my readers (all '6'* of you).  We can all go straight to where the good, substantial, material is, and learn something!

The first paper shows that Antarctica has been losing mass -- Increasing rates of ice mass from the Greenland and Antarctic ice sheets revealed by GRACE (also available from thingsbreak -- I hope he's gotten appropriate permissions.) -- and that the rate of mass loss has been increasing in recent years.  It's not just a simple linear decline.  Rather, the mass loss is not only getting more negative (losing more mass year by year), but the rate it's going more negative is getting even bigger (the increase in mass loss from year to year is getting bigger too).

The second paper shows that in the last couple of years, snowmelt -- only one of the several ways that the Antarctic can lose mass -- has been lower than usual, with the most recent year being the lowest snowmelt year of the last 30.  An updated Antarctic melt record through 2009 and its linkages to high-latitude and tropical climate variability, also at thingsbreak.

So what do we have?  Well, in all seriousness, it's a couple of interesting papers on the science (yay!) and not a whole lot of conflict today.  But we may take a sign of something to keep reading the scientific literature for.  We have on one hand, observations that the total mass lost by the Antarctic ice sheet is going up (over the 6 years that this data source is available).   On the other hand, we have observations that the summer 2008-2009 was a low point for surface melting (of the 30 years this has data for).  But we know that's just one of the many ways the ice sheet can lose mass. 

What we keep reading the science for are:
1) Do either data analysis continue to get support from later observations?  When we're looking at relatively new approaches, which both are, one of the things we have to keep in mind is that the method might be wrong somewhere.  Both look plausible to my non-expert (in these methods) self.  But the real story will be told over the next couple of years as people seriously expert in these methods start doing their own work, and the original authors keep after the issue.  Keep your eyes peeled for more.
2) Only one of the mass sinks for the Antarctic has been examined directly.  Look for (some articles may exist already) or keep your eye out for new articles to come on those other mass loss mechanisms.  It might be that when we add up the individual mass loss mechanisms we don't match what people observe from GRACE.  Such a thing happened in the early 1990s regarding the sinks for CO2 -- the observable amount taken up by the ocean was much too small.  That told us something else (land uptake) was going on.  (In this case, maybe we discover that GRACE isn't accurate about the total mass loss.  Or maybe it's that snowmelt isn't accurately inferred, or iceberg loss, or ....  If we've got many things involved, and we do, then any of them could be the cause of a discrepancy.)

Either way, the serious resolution of a conflict, if there is one, will take place in the scientific literature.  At the moment though, there's no conflict.  Just some interesting science that suggests we have more to be looking for (as the GRACE and the snowmelt methods get more data) and other interesting science to look for, or keep our eyes out for.

* I realize, and appreciate, that I have more than 6 readers.  I'm minded, though, of a local radio person I listen to, who talks of his '13' listeners.  Probably more like 130,000.  (I just wish I were understating as thoroughly as him!).  The thing being, I do realize that this is not one of the higher-traffic blogs around, or even around and on topics somewhat like mine.  I therefore appreciate those of who who read, and who contribute substantive comments. 

Detail: Antarctic Snow and Ice

0 Catching up on sea level

Bit of a place holder while I finish two other sea level things -- faq update, and comments on the Nature paper.

One important bit, which I was reminded of in email:
A good decade before the Noerdlinger and Brouwer paper, Phil Hays had mentioned to me that the ice shelves were a good 10 times the sea level effect of sea ice.

The sea level FAQ of mine I mentioned is quite old. What you see at the moment is the 1997 version, which is only minorly different from the 1991 version. I leave the 1997 available because as it's been cited in the professional literature, I do want that exact version available. Still, a fair amount has changed in the last 15 years. Not the main emphasis, which is largely time-independant. But many details are now in need of revision. Among them are: glaciers are more significant than my casual writing there suggested, Greenland is much less stable than indicated (recent discoveries), West Antarctica may be rather more stable.

Vernon: Maybe you could do some rewriting of your note(s)? I still can't figure out why you think my FAQ is misleading. My main point is that the sea level effect of sea ice is not zero, though it is a small number. Your conclusion is that the effect is not zero, though it's a small number. Note that the faq predates the Rothrock paper you mention. Also note that a) sea water's density dependance on temperature is somewhat different than fresh -- enough to matter for this situation b) global mean ocean water temperature is 3.5 C, not 20 (and at colder temperatures, the density depends less on temperature) c) you've assumed that all energy to melt the ice comes from the ocean, which is physically unlikely. As, to be sure, is it unlikely to be entirely from the atmosphere (which was effectively my take). The reason for my taking it all from the atmosphere was to isolate the haline effects of melting the ice from the thermal effects. Plus, the sea ice is usually in water colder than global average, i.e., very near freezing (by which time, the density dependance of sea water on temperature is very much smaller, about 16x if I remember right, than on salinity).

One feature of the sea level business is that once you try to attain accuracy, it gets very messy very quickly. c.f. Jay Alt's comment:

Even the 'simplest' calculations of sea level rise from earlier decades contain at least 10 components that influence the result. Tides, temps, winds, . . .

Here is a very nice resource from James Titus, who examined these issues in depth for EPA.
http://users.rcn.com/jtitus/
http://www.climatesciencewatch.org/index.php/csw/details/epa-titus/

I've looked at the links and they're nice -- readable by nonprofessionals without losing the science.

The Nature paper http://www.nature.com/nature/journal/v458/n7240/full/nature07933.html is indeed interesting. It's also just far enough from my areas that it's difficult for me to be sure that something was missed, as opposed to being too obvious to mention in a professional setting. In short, though, it looks good and interesting, but may not mean quite what some of the press stories are suggesting. More to come.

Detail: Catching up on sea level

0 Ice and sea level

Melting sea ice or ice shelves can indeed change sea level. It turns out that I was probably the first person to compute by how much the sea ice can do so, and there's a story for tomorrow about why I wasn't the person to publish this in the scientific literature even though I had the answer more than a decade before the next person to look at the problem.

The first peer-reviewed investigation was published by Peter D. Noerdlinger and Kay R. Brower, in The Geophysical Journal International, 170, pp. 145-150, 2007 The melting of floating ice raises the ocean level. The DOI is 10.1111/j.1365-246X.2007.03472.x You can get the authors' copy at the linked title. They included a simple experimental demonstration as well, which I hadn't done. I also didn't think about the ice shelf contribution, which turns out to be 10 times larger than sea ice's. Oh well.

The wrong answer on this question is to say that a floating body displaces its own mass, so when it melts, the water level is unchanged. Now, as this is partly quoting Archimedes and he was an awfully bright guy, there's at least good company.

The reason it fails (and, by the way, it isn't clear that Archimedes didn't know about this) is that what is melting when we melt sea ice or ice shelves is not the same stuff as what it is floating in -- sea water. Sea water is salty, about 3.5% salt. Sea ice is fairly fresh, about 0.5% salt. And ice shelves are completely fresh. If we were melting ice shelf in to fresh water, the level would indeed not change. You can test this with a glass of water and some ice cubes. To find just what happens when you melt frozen stuff that's floating in a liquid, you have to do the math. I've got it in my Sea Level Change FAQ. The result is, sea level rises slightly. I found a few millimeters (about 4) for sea ice. Noerdlinger and Brower found a few centimeters (also about 4) for ice shelves. It isn't much, but it isn't exactly zero.

A way to think about what happens, minus most of the math, is to envision a block of ice floating in the ocean. The density of ice is lower than ocean water -- about 917 kg per cubic meter for ice, versus 1028 kg per cubic meter for ocean water. The difference is why '90'% of an ice berg is below the surface. Conversely, 10% is above the surface. It's actually (1028-917)/1028 above the surface, 10.8%. Now melt the fresh ice, but don't let it spread out or mix with the ocean. That gives us a material with density near 1000 kg per cubic meter. That blob, for the same reason that the ice was floating in the first place, sits (1028 - 1000)/1028 of itself above the water level -- 2.7%. That bit sticking above water level means that melting such ice does contribute to sea level change. If the density of the stuff you melt is different than the stuff it is floating in, you can indeed have a rise (or fall, if the melt is denser than what it floats in) in fluid level.

This example is also why I, in particular, and scientists more generally, want you to 'show me the math'. The thing is, when I first wrote the sea level FAQ, I made the same error as everybody else was making. It was an early commentator (Rick Chappell) who told me I was wrong (he didn't have the math, but did have the above principle) that prompted me to work out the math in detail. I was doing show just to show him in detail that he was wrong. In fact, at the end of my calculation, I'd shown myself that I was wrong. So updated the FAQ and my thanks to Rick. Merely asserting principles would not have changed anybody's mind. The problem being that, although a principle might be true (if I jump, the earth moves the other way), the effect might be too tiny to worry about. It's only when we do the math, get quantitative, that we can decide whether something is too tiny or not.

A slightly different example, prompted by this point going back to ancient Greece. There is an Aristotelean (or at least his time) principle that "Nature abhors a vacuum." Now, for many purposes in daily life, this is not a bad principle. If you try making a vacuum, you'll need to do things to shield it against nature trying to fill it back up. On the other hand, it was also an argument that there were no such things as atoms. The argument being, if there were atoms (discrete bits of matter) then there would be gaps between the atoms. But those gaps would be vaccum -- and 'nature abhors vacuum'. Now that we know that there are indeed atoms, the principle applies, but it is directed to how nature responds, and in which cases.

Detail: Ice and sea level

0 Another one bites the dust

Another ice shelf bites the dust, to little surprise in the polar community. In this case, it's the Wordie ice shelf, and you can see a photo and a short write up at:
http://www.reuters.com/article/environmentNews/idUSTRE5332BU20090404

The reason I'm not surprised, and anybody who has been reading the science is not surprised, is that we knew years ago that warming was going to lead to the breakup of ice shelves. See, for example:

Rapid disintegration of the Wordie Ice Shelf in response to atmospheric warming, by C. S. M. Doake & D. G. Vaughan. That was 1991. You do have to remember that glaciologists are used to things that move at glacial speeds.

The breakup was more specifically tied to atmospheric warming in a more recent (1996) paper by D. G. Vaughan & C. S. M. Doake Recent atmospheric warming and retreat of ice shelves on the Antarctic Peninsula. The authors cite the earliest suggestions of problems for Antarctic ice shelves in a warming world as Mercer's 1978 paper
West Antarctic ice sheet and CO2 greenhouse effect: a threat of disaster. Rather drastic title. But it serves to both establish that the collapse of these ice shelves due to CO2-induced climate change is an old issue, and to provide yet another example of a scientist in the 1970s who was not expecting 'another ice age' any time soon.

The scientific question left on ice shelf collapses on the Antarctic peninsula is not whether, but which one is going to go next, and how soon. For the ice shelves farther to the pole -- which are the big ones and of the greatest concern (the reason for the 'threat of disaster' in Mercer's title) for the future, we still have several scientific questions about whether, and what happens how fast if they do go.

Some folks are making comments which mix up sea ice and ice shelves. Please don't do that! See my note about ice types for the simple differences between the sorts of ice.

It's also been mentioned that the breakup of ice shelves can't change sea level. This isn't actually true. I'll take up the details in two notes to come. First, why it isn't true (you can get ahead by reading the Sea Level Change FAQ -- same process that means sea ice can change sea level applies to ice shelf ice). Second, why it is someone else published it first, even though I had the answer 10 years earlier. A bit of how science is done, and reminder that scientists are fallible.

Detail: Another one bites the dust