Reading a quora debate on the effects of sea level rise, I found three statements that I thought QI in different ways:

1. A claim that if the Greenland Ice Sheet entirely melted this would not raise sea levels around Scotland because the increase in water volume would be offset by the reduction in gravitational attraction of all that ice, so sea levels would rise more near the Equator, and not at all at Scotland. I’m skeptical about this one. Obviously the effect is real, but would it really have such a large effect? Anyone have any numbers on this?

2. Sea levels are not affected by melting sea ice, they are affected by ice moving from land to water. Sea levels could therefore rise much more quickly than calculations based on rate of melting would suggest. If for instance a glacier moved from an equilibrium situation to one where ice flowing down was moved out to sea by currents. Do current estimates take this sort of mechanism into account?

3. A suggestion that the Piri Reis map of 1513 accurately shows the Antarctic coast in the location of the actual land, free of ice. This proves that Antarctica has been free of ice within recent human history, so all this talk of melting ice causing sea levels to rise is just nonsense. It would be nice to think that the guy who posted this one was trying to be funny, but I suspect he was absolutely serious. He really thinks that an ancient map that is known to be wildly inaccurate is more reliable than careful scientific investigation.

I suppose I should post the link as well:

https://www.quora.com/If-all-the-ice-in-the-Antarctica-melts-which-countries-in-the-world-will-be-entirely-covered-in-water

wiki

“A more sober analysis of these claims was published by Gregory McIntosh, a historian of cartography, who examined the map in depth in his book The Piri Reis Map of 1513 (Athens and London: University of Georgia Press, 2000). He was able to find sources for much of the map in Columbus’s writings. Certain peculiarities (such as the appearance of the Virgin Islands in two locations) he attributed to the use of multiple maps as sources; others (such as the errors in North American geography) he traced to the continued confusion of the area with East Asia. As far as the accuracy of depiction of the supposed Antarctic coast is concerned, there are two conspicuous errors. First, it is shown hundreds of kilometres north of its proper location; second, the Drake Passage is completely missing, with the Antarctic Peninsula presumably conflated with the Argentine coast. The identification of this area of the map with the frigid Antarctic coast is also difficult to reconcile with the notes on the map which describe the region as having a warm climate.”

The Rev Dodgson said:

Reading a quora debate on the effects of sea level rise, I found three statements that I thought QI in different ways:

1. A claim that if the Greenland Ice Sheet entirely melted this would not raise sea levels around Scotland because the increase in water volume would be offset by the reduction in gravitational attraction of all that ice, so sea levels would rise more near the Equator, and not at all at Scotland. I’m skeptical about this one. Obviously the effect is real, but would it really have such a large effect? Anyone have any numbers on this?

2. Sea levels are not affected by melting sea ice, they are affected by ice moving from land to water. Sea levels could therefore rise much more quickly than calculations based on rate of melting would suggest. If for instance a glacier moved from an equilibrium situation to one where ice flowing down was moved out to sea by currents. Do current estimates take this sort of mechanism into account?

3. A suggestion that the Piri Reis map of 1513 accurately shows the Antarctic coast in the location of the actual land, free of ice. This proves that Antarctica has been free of ice within recent human history, so all this talk of melting ice causing sea levels to rise is just nonsense. It would be nice to think that the guy who posted this one was trying to be funny, but I suspect he was absolutely serious. He really thinks that an ancient map that is known to be wildly inaccurate is more reliable than careful scientific investigation.

All three are total bull, as you are no doubt aware.

However, sea level rise will be less in Scotland because of isostatic rebound. The area of Scotland is still rising following the loss of ice at the end of the last ice age. Here’s a world map of isostatic rebound, from Wikipedia. Scotland is rising at a rate of about 1 mm per year, Finland at up to 6 mm per year, and parts of Canada at higher rates.

I don’t think that No. 2 is total bull at all. I think it is quite likely a significant factor in ice-melting that is under-accounted for.

And 3 is a totally different league of total bull to 1.

The Rev Dodgson said:

I don’t think that No. 2 is total bull at all. I think it is quite likely a significant factor in ice-melting that is under-accounted for.

And 3 is a totally different league of total bull to 1.

I haven’t bothered to think it right through, but no 2 got me thinking in terms of ice having more volume than liquid water – by a reasonable amount, given that you always were told when I was a child to leave an inch of air in your flask before putting it in the freezer. And this would matter in a melting sea ice scenario.

The Rev Dodgson said:

Reading a quora debate on the effects of sea level rise, I found three statements that I thought QI in different ways:

1. A claim that if the Greenland Ice Sheet entirely melted this would not raise sea levels around Scotland because the increase in water volume would be offset by the reduction in gravitational attraction of all that ice, so sea levels would rise more near the Equator, and not at all at Scotland. I’m skeptical about this one. Obviously the effect is real, but would it really have such a large effect? Anyone have any numbers on this?

2. Sea levels are not affected by melting sea ice, they are affected by ice moving from land to water. Sea levels could therefore rise much more quickly than calculations based on rate of melting would suggest. If for instance a glacier moved from an equilibrium situation to one where ice flowing down was moved out to sea by currents. Do current estimates take this sort of mechanism into account?

3. A suggestion that the Piri Reis map of 1513 accurately shows the Antarctic coast in the location of the actual land, free of ice. This proves that Antarctica has been free of ice within recent human history, so all this talk of melting ice causing sea levels to rise is just nonsense. It would be nice to think that the guy who posted this one was trying to be funny, but I suspect he was absolutely serious. He really thinks that an ancient map that is known to be wildly inaccurate is more reliable than careful scientific investigation.

I haven’t read the whole thread so I am sorry if I am answering already answered questions but

1/ The Greenland ice sheet’s mass is a bit less than a millionth that of the Earth. Its melting will not significantly affect the gravitational potential or field strength in Scotland…

2/ The IPCC reports certainly mention and account for changed rates of glaciation.

3/ Antarctica was first sighted by humans in 1820, and was not significantly mapped until late in the 19th century.

dv said:

I haven’t read the whole thread so I am sorry if I am answering already answered questions but

1/ The Greenland ice sheet’s mass is a bit less than a millionth that of the Earth. Its melting will not significantly affect the gravitational potential or field strength in Scotland…

I think moll has this one right. The guy has just got the rebound effect mixed up with direct gravitational effects between Greenland and Scotland.

dv said:

2/ The IPCC reports certainly mention and account for changed rates of glaciation.

But have they got them right? The mechanisms would be very complex, and I’m skeptical that they have been modelled reliably.

dv said:

3/ Antarctica was first sighted by humans in 1820, and was not significantly mapped until late in the 19th century.

Yes, the Wiki-link gives a reasonable history of the particular map, and the exploration of Antarctica.

The Rev Dodgson said:

dv said:

I haven’t read the whole thread so I am sorry if I am answering already answered questions but

1/ The Greenland ice sheet’s mass is a bit less than a millionth that of the Earth. Its melting will not significantly affect the gravitational potential or field strength in Scotland…

I think moll has this one right. The guy has just got the rebound effect mixed up with direct gravitational effects between Greenland and Scotland.

Good.
Note that isostatic rebound takes thousands of years so it won’t help us for time scales in the tens or hundreds of years.

dv said:

2/ The IPCC reports certainly mention and account for changed rates of glaciation.

But have they got them right? The mechanisms would be very complex, and I’m skeptical that they have been modelled reliably.

Well there are uncertainties in all of this stuff. You should see the error bars on the clathrate inventory.

dv said:

3/ Antarctica was first sighted by humans in 1820, and was not significantly mapped until late in the 19th century.

Yes, the Wiki-link gives a reasonable history of the particular map, and the exploration of Antarctica.

Jolly good.

The Rev Dodgson said:

I don’t think that No. 2 is total bull at all. I think it is quite likely a significant factor in ice-melting that is under-accounted for.

And 3 is a totally different league of total bull to 1.

Oh, I should have added. No. 2 as a mechanism is perfectly valid. But doesn’t need stating because it’s already been included in every sea level rise calculation since the year dot. It’s at least 15 years since I first saw it explicitly stated in a scientific paper about sea level rise, and it would have been very well known even back in the 1980s.