Tuesday, September 20, 2016

Try reading the next sentence in the article, Professor Rotunda

Comments at Eli's previous post led me to Chris Mooney's fun and games at WaPo, reporting on some law professor talking about how a Harvard researcher showed that melting Greenland will lower regional sea level for places like the Netherlands and therefore it's all great. When pressed skeptically by physicist/Congressman Bill Foster who says the overall effect must be to raise sea level, Prof Rotunda says, "Read his article, that's what he says".

Okay, let's do that! Here is Harvard's Jerry Mitrovica:

When an ice sheet melts, that gravitational influence diminishes, and water moves away from the ice sheet, causing sea levels to drop as far as 2,000 kilometers away. (The drop is most pronounced close to the glacier, because gravity’s effects dissipate with distance.)
Vindication! Unless of course the very next sentences tell us something additional:

But because the sea level has fallen where the ice sheet melted, it rises everywhere else beyond that 2,000-kilometer boundary, and on distant shores this rise is far greater than the global average. The effect amplifies the rise in average global sea level attributable to the addition of the meltwater itself to the oceans. 

Either Prof. Rotunda had failed to read more than two and one-half paragraphs of an article he discusses in Congressional testimony at some length, or he's being deceptive.

On top of that, three other points. First it's not clear that the 2000 km range is a net effect after considering the effect of increased ocean volume from melt, or just the range of discernible gravitational effect. If the latter, then Rotunda's claim that Netherlands gets a benefit is misplaced in yet another way. The quote is in a mainstream magazine, not peer reviewed. I thought I was being lazy by not finding the original publication, but besides not knowing where it is, I'm not testifying to Congress right now.

Second, Greenland is big. Rotunda seems to think a magical gravity shield protects any place in Europe that's within 2000 km of any place in Greenland from all Greenlandish impacts. If most of the mass loss in Greenland is more than 2k away, it doesn't matter if some of it's closer - the net effect is worse than not considering gravitational effect.

Third, Rotunda needs to pull out a ruler and a map. Google Earth says no part of Netherlands is within 2000km of any part of Greenland's ice cap. I wonder if he did the miles/kilometer mixup, but maybe I'm just giving him too much credit. He says Europe doesn't need to worry about Greenland, but except for Northern UK, Ireland, and part of Scandinavia, no part of Greenland is with the magic distance Rotunda is discussing.

11 comments:

Entropic man said...

Professor Rotunda failed to mention Antarctic gravity and melt.

Greenland ice sheet melt will produce the maximum sea level rise in the Southern Hemisphere.

Antarctic ice sheet melt will have maximum effect on Northern Hemisphere sea level.

I suspect that the crossover between sea level decrease and sea level rise will not be 2000km from the ice sheets. Once the effect of melting in the Antarctic is taken into account, the crossover will be a lot closer to Greenland.

With different geography in Arctic and Antarctic and no reason for melt to be smooth, we may even get sloshing. Scotland may see rapid changes in sea level, up and down.

Kevin O'Neill said...

You might expect more than simple quote-mining from someone appearing before a congressional committee. You might. You'd be disappointed.

jrkrideau said...

@ Kevin O'Neill

One must remember Ed Wegman and Lork Monction both have testified before Congressional committees.

The standard of witness before Congress is not high. Prof. Rotunda is maintaining that demanding stanard

Rotunda is a real name? Between his name and his appearance I thought he was a Walt Disney creation which would probably match Republican scientific knowledge.

Fernando Leanme said...

The Greenland ice isnt going to melt. A portion is likely to melt at the edges. We will have to see what happens to snowfall over the next 100 years to understand whether the Dutch need to panic. I'm a few meters above sea level, so I think I should be ok.

BBD said...

The Greenland ice isnt going to melt.

Don't be painfully stupid, Fernando. It's already melting now. More will melt as temperatures rise.

A portion is likely to melt at the edges.

Just like it did during the Eemian, when the GrIS seems to have contributed about 2m to the ~6m sea level highstand (NEEM Community Members, 2013).

We will have to see what happens to snowfall over the next 100 years

Greenland is experiencing annual ice mass *loss*. This includes snowfall.

At least try, Fernando.



Bryson said...

Nothing original here, but the Republican Party has clearly given up on arguing facts-- it's all grift, all the time. They pose a clear and present danger to the US, and to the wider world.

Wombat said...

Tamino has a good post on this at https://tamino.wordpress.com/2016/09/17/two-fools-and-a-scientist/.

"First it's not clear that the 2000 km range is a net effect after considering the effect of increased ocean volume from melt, or just the range of discernible gravitational effect."

In fact it is the former. The line where sea level remains constant if only Greenland melts runs through Scotland. There is a discernible effect for most, if not all, of Europe, which has a lower rate of sea level rise than the global average for precisely this reason.

This will not save Holland - and certainly not New York.

The bright spot is that as the ice sheets melts the oceans retreat from them reducing the ability of warm water to melt the ice.

BBD said...

The bright spot is that as the ice sheets melts the oceans retreat from them reducing the ability of warm water to melt the ice.

My understanding is that melt from the GrIS raises sea level around the Antarctic, destabilising the drainage glaciers from the WAIS (and sectors of the EAIS) and increasing ice mass loss from those ice sheets.

There is an overlooked element of positive feedback.

Wombat said...

"My understanding is that melt from the GrIS raises sea level around the Antarctic, destabilising the drainage glaciers from the WAIS (and sectors of the EAIS) and increasing ice mass loss from those ice sheets.

There is an overlooked element of positive feedback."


True but the melting of the WAIS reduces local sea level which is negative feedback. Local melting lowers local sea levels, distant melting raises local sea levels. My understanding is that on balance gravitational effects are going to lower sea levels around the WAIS. That does not, of course, mean that the WAIS is safe.

Aaron said...

GrIS will not "melt", it will undergo a progressive structural collapse. Let me rephrase that:It is undergoing a progressive structural collapse. see for example: (https://worldview.earthdata.nasa.gov/?p=arctic&l=VIIRS_SNPP_CorrectedReflectance_BandsM3-I3-M11(opacity=0.75),VIIRS_SNPP_CorrectedReflectance_BandsM11-I2-I1(opacity=0.58),VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Reference_Labels(hidden),Reference_Features(hidden),Coastlines(hidden)&t=2016-09-09&v=-550400,-3257856,104960,-2805248) for 2016 sep 9

The result will be a slurry resulting from calving off of ice faces greater than ~100 meters high. The slurries can flow down any grade greater than 2%. In the fjords/water, the ice will roll, causing cavitation that can erode basalt at rates of meters per day. Our hope is that the crystalline rocks in the SW side of GrlS will erode more slowly than the Colombian Basalt below Lake Missoula.

The outflows of Lake Missoula were also progressive structural collapse. The wave benches resulted from shallow supraglacial lakes.(Do the math. The rock boys that wrote the books, did not do much math.)

Ice dams can only withstand a head of a little more than 6 meters, due to pressure reduced melting points. More than 6 meters of head from from liquid water, and they "hydrofracture". Sometimes it takes a while for the cold ice to come into thermal equilibrium with the water, but that is a matter of years, and not generations.

BBD said...

Whilst unwilling to get all pedantic about the process that turns an ice sheet into sea water, there's this, just off the press:

Greenland ice is melting seven percent faster than previously thought.