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Bolstering Alarm Over Scientists' Warnings, New Study Finds Sea Level Rise Projections 'Are On the Money'

As I stated, it isn’t what you said, it is the manner in which you stated it, and most importantly the understandings and framings that you chose to leave out of your screed, which dramatically alter the impressions of the work you quoted and your manner in dismissing the understandings that these reports portray in their fuller discussion and explanations. (often labelled “cherry-picking,” I believe).

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Climate is warming, climate is an averaging of weather trends over a period of decades. The smallest interval of Climate, is 3 decades. looking at the last 300years there would only be 10 relevant climate points, plot these on a graph and the rise is dramatic and accelerating, without anything resembling respite aside from some “leveling” in the climate periods which include the last half of the '60s and the first half of the '70s, and this is suitably explained by the post WWII global industrial expansion that ejected a lot of sulphur compounds from the combustion of coal into our upper atmosphere, inducing some significant rejection of solar emissions from our upper atmosphere.

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My intention was to make exactly that point about ADV’s comment, by making his or her cherry picking starker. Since it’s almost impossible to satirize today’s Republicans, such explicit clearness as yours is usually necessary and I probably would have gotten to it eventually. Thanks for saving me the trouble.

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I suspected such at first, but it is so difficult to judge this any more now that so many seem so ready to vent their inner crazy, and then vehemently defend their crazy, that I feel compelled to over-explain. Apologies if I stepped a bit over the line, this is the issue that finally drove me back to engaged political discussion and involvement.

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OK, so according to ~https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level, the rise between 1970 and 2020 is 131 mm or a bit over 5". Are you saying you’d be expected to notice this? The tides in FL are around 1.5 ft from low to high - so it is a significant fraction that you might have noticed if you really had been paying attention and had put markers on a fixed object, but otherwise I doubt many people can tell.

By 2100, that won’t be true anymore as the pace in mm/yr rise is going to keep going up.

Al Gore’s 20 ft number (for which I guess he didn’t even give a time span in the predict for: ~https://scienceline.org/2008/12/ask-rettner-sea-level-rise-al-gore-an-inconvenient-truth/) probably didn’t help since I hear conservatives all the time claim how far off he was, but even 1.5 m by 2100 (which would be about 10x the rise you’ve seen in 50 years) is kind of a big deal. None of us will be around much after 2100, but it isn’t inconceivable it gets to 20 ft or more after that. If everything melts it goes up 230 ft (not including expansion). Let’s hope people figure some things out way before it gets that bad.

I’m using a seawall as a reference, and really, it doesn’t look like it has changed at all since 1965; an inch might not be noticeable but 5"? yes. There are drains that come in at about a foot above water level - still the same distance. Actually there are studies that show inital melting of the ice caps may actually result in a DECREASE in sea levels. Counterintuitive yes, but the science seems to make sense. ~https://www.sciencemag.org/news/2016/02/how-melting-ice-sheet-could-actually-lower-sea-level-some-places

@trog @dpearl

That is an amazing link. I trust that source otherwise I would say off the cuff that it is pseudoscience. An ice sheet on Greenland contributes enough gravitational pull so when it’s gone the water level goes down? And by 50m in Scotland? I’d be curious to try some back of the envelope equations because that seems crazy. So does that mean areas in Alaska with huge mountains next to the oceans have much higher sea levels than would be expected if the mountains were way inland instead? By 50 meters?

I’m kind of flabbergasted to say the least.

And as far as ocean levels not equalizing like a bathtub I don’t get that either. I would think they would do that though of course always on top of that equalization would be tides and wind (usually a smaller effect I thought unless it’s a big storm).

And the idea that Greenland is going to pop up a significant amount without the sheet of ice on top - huh?

Somebody help me out here.

I know exactly how you feel. Dealing with planetary-sized gravitational forces might be as simplistic as we think. I thought you would find the concepts interesting.

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Well, I’ll have to wait on that article that is talking about the future Greenland ice sheet melt, but historically it appears that Florida has been about 2mm yr rise according to ~https://www.flseagrant.org/wp-content/uploads/2012/02/SLR-Fact-Sheet_dual-column-letterhead_8.2.13_pdf.pdf. Some places more some less. 2 mm per year in 50 years is about 4”. So maybe Florida doesn’t see the full average rise or maybe I’ve got some round off error, but you should see something. So you think it is less than 3” over this time?

I could be wrong; I’m just saying it looks about the same to me -

@trog @Senior_Citizen_71

Seems to me that the key point about climate change that the public does not appreciate is the latitudinal gradient in how things affect us - and this is another example of that. However, I agree with you that I need a back of the envelope calculation that helps me understand the magnitude of the effect near a place like Scotland (50m or 50cm?). Since this article is from 2016 - I’ll try to explore this more.

The 50 meter fall number near Scotland is the correct numerical value - but was just under a pretend scenario where only the Greenland ice sheet melts (and global averages go up by about 7 meters). Similarly, they show that if only the Western Antarctic ice sheet melts the local fall in sea level will be on the order of a hundred meters. A quick look at the literature shows a whole bunch of interesting articles from Jerry Mitrovica and/or Natalya Gomez on the importance of gravitational effects of ice sheets melting over the next 100 years - and the resulting differences between local effects and global average effects in sea level changes. They also discuss the interconnectedness of the changes in the ice sheets and in no way are predicting that just a single giant ice sheet will collapse in an instant while others stay basically unchanged.

@trog @Senior_Citizen_71

I’ve been reading about the Geoid (~https://en.wikipedia.org/wiki/Geoid, ~https://oceanservice.noaa.gov/education/tutorial_geodesy/geo03_figure.html, ~https://oceanservice.noaa.gov/facts/earth-round.html, ~https://oceanservice.noaa.gov/facts/geoid.html, ~https://oceanservice.noaa.gov/facts/earth-round.html) and I think I understand the general concept better now. From the last link:

If one were to remove the tides and currents from the ocean, it would settle onto a smoothly undulating shape (rising where gravity is high, sinking where gravity is low).

And then this shape is extended across land too based on gravity measurements. I was first confused, thinking areas of higher gravity would have a lower sea level - thinking of at as “flattening” what was above it. But the described dynamic is that areas of high gravity steal water from areas of low gravity and thus the ocean level is higher. So far I haven’t come across any quantitative comparison of contributions to gravity change from mass above to mass below the geoid. In fact, I was surprised to read from ~https://oceanservice.noaa.gov/education/tutorial_geodesy/geo07_gravity.html

Imagine if all of the Earth topography, mountains and valleys were scoured off leaving a continuous world’s ocean completely at rest, without the effects of currents, weather and tides. The effect of the Earth’s gravity on this hypothetical world mean sea level is represented by the geoid. However, because the Earth’s gravity is not equal in all places, this hypothetical ocean is not perfectly smooth. The strength of the Earths’ gravity, and consequent effect on the shape of the geoid is represented by color variations in this image.

actually that’s a bit off according to Wikipedia as it doesn’t take into account variations of density in sea water - but close enough - I like the precise definition given on Wikipedia better:

All points on a geoid surface have the same effective potential (the sum of gravitational potential energy and centrifugal potential energy).

That NOAA link makes it sound like the effect of gravity from mass above the ocean is insignificant (though I realize that may not be the intention of this paragraph). I’ve heard that with very accurate gravimeter you can tell the difference between being next to a mountain and moving away from it, but I always assumed this was such a small effect as to not effect the oceans (or now I would say affect the geoid).

But I do see the Wikipedia article mentions mass above the earth (I’m still quite impressed with Wikipedia - I found their article better than the ones at NOAA) - I need to donate to those guys some more.

a smooth but irregular surface whose shape results from the uneven distribution of mass within and on the surface of Earth

So when I look at the Geoid at (~https://upload.wikimedia.org/wikipedia/commons/4/4a/Geoid_undulation_10k_scale.jpg), I see a variation of around +/- 100m (the exact min and max are given in the article as -106 and +85) which is measured against the closest fitting ellipsoid to the geoid. But when you look at these maps - they aren’t so obviously affected by mountain ranges (maybe a few m, but I don’t see a 50m effect) and given the total range and the fact that way way more mass is involved under the surface of the earth, it still doesn’t make sense that loss of a Greenland glacier could cause a 50m change in the Geoid.

I’m now trying to search for links using glacier affect geoid. If anyone has something good, let me know.

Presumably, the loss of ballast weight on Greenland will render it more buoyant and it will rise, and the ice loss on top will be replaced by magma underneath. There may be a net loss of altitude for the stack, but the resultant stack will also be more dense and the mean mass will be about the same if you add the mass of the magma which filled in as the floating rock rose. I can imagine the loss of altitude having a very localized effect on gravity, but not out to hundreds or thousands of kilometers away, especially given the curvature of the Earth.

However, glacial rebound takes time, and while it is rising, it will presumably have a gravity deficit in the area, so it’s just a question of whether this deficit could have an effect large enough to lose 50 meters of sea level in the region. I don’t know what it would take to even nail down all the variables that would be required to do such a monstrous calculation (this might be a job for computer modeling), but backing off and looking at the overall picture, 50 meters of sea level is a large chunk of the total global magnitude of deviation from the ellipsoid, so if the effect is as large as 50 meters, it seems like we should already be seeing such an effect right now. After all, the ice on Greenland used to be miles thick at the last glacial maximum, and Greenland today is still rebounding from the large loss of ice load from that time, so presumably, it is currently experiencing the very sort of glacial gravity deficit that is being postulated here. So if the effect is as large as suggested, then it should be visible both on the gravity maps and the sea level maps. Instead, what I’m seeing on the gravity maps is a large gravity surplus region that overlaps onto Greenland, and I don’t see a marked difference between the on-land and off-shore surplus levels. And on the sea level maps, the seas around Greenland are showing a rather large surplus sea level above the ellipsoid–at a time when supposedly it should be experiencing a large deficit due to the previous loss of ice.

So my hunch would be either the glacial effect is too small to be noticeable against larger-amplitude gravity deviations caused by deep density variability, or, the density surplus under Greenland just happens to be the right shape and magnitude to exactly cancel and disappear the previous post-glacial gravity deficit, and the already high sea levels around Greenland would be extraordinarily high without the ice-loss effect. Both are possible, but my feeling is that the cancellation option would require an improbable combination of coincidences and statistical outliers. So I’m highly skeptical of the postulated 50 meter loss as well.

But on a frivolous tangent, this geoid issue reminds me of an amusement project I’ve wanted to do for many years, but haven’t yet figured out an easy or practical way to do it. As the water piles up over a gravity surplus anomaly, it assumes a surface of equilibrium so that as you sail over the anomaly, a plumb line will always be perpendicular to the local surface. That means that if you could solidify that bulge into a smooth surface at the mean sea level, you could drop a ball onto it at any point on the bulge and it would have no tendency to roll in any direction, even if the bulge were so extreme as to be a visible hill. But we have another attractor that operates a lot like gravity, though at a very different scale. So if you had a powerful stable magnet and a steel ball, presumably there would also be a surface of equilibrium between gravity and magnetic attraction such that when placing the steel ball at any point on that surface, it would likewise have no tendency to roll in any direction. Or, if the surface was hard and smooth enough, you could roll the steel ball over the equilibrium shape and it would have a steady speed loss similar to what it would experience on a similarly smooth “flat” surface. With an elevated magnet, this might even produce an equilibrium surface which goes past vertical. With multiple magnets, more complex equilibrium topographies might be possible.

I know this would only work with a steel ball of a specific size, and even with stable magnets, it might only perfectly “level-out” at a specific temperature. And I don’t know that it would have any useful application. But if you surrounded such a topographical surface with a bowl so that the ball would roll back and forth through the shape-field, I think that would be at least as interesting and trippy to watch as a Newton’s cradle.

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