Why is sea level rise worse in some places?

In Scandinavia, isn't it glacial rebound rather than tectonic?

The absolute value of gravity is (to oversimplify) the sea-level datum for current generation datums, like the delayed NGS (nominal year) 2022 datums.

They've (NGS) been flying absolute gravity measurement equipment in planes with precision GPS and lidar since ~2005 as part of the GRAV-D program.

Additionally, slight 'variations' (ie deviations from the expected circular/elliptical) in the orbits of GPS satellites can be used to infer slight variations in the gravity below.

Separately, the military likely has had all of this measured and modeled for decades as part of ballistic missile targeting, but remains mostly classified at useful resolutions.

The transitions from NGVD27 to NAVD88 to the work-in-progress 22 datum is exactly because the idea of a simple "universal" sea-level doesn't exist in the manor you would expect it to.

But even with the GRAV-D based datums, the actual observed water levels will occur at slightly different datum heights in different locations, for various geophysical reasons.

The melting of glaciers themselves can have an impact on gravity, causing water levels to drop around them. https://www.theguardian.com/environment/ng-interactive/2018/...

PDF of gravitational correction factors by geographical region for use in theoretical weighscale calibration (vs calibrating with actual test weights): https://hardyinst.custhelp.com/app/answers/detail/a_id/1588/...

Not true.

First of all, most of the temperature rise only happening close to the surface with average surface temperature rise being only about 1.5F or 1C since 1901.

This article says deep ocean water is projected to warm up by only 0.2C during next 50 years: https://www.openaccessgovernment.org/deep-ocean-warming-subt...

Furthermore, at around 4C which is what deep ocean water is close to (everything below 200m is essentially 4C), thermal expansion is almost nil. For colder water thermal expansion is actually negative.

4C is when water is at its densest. It is not an accident that all oceans are 4C, because 4C water sinks to the bottom and anything colder or hotter than 4C floats up. This remarkable property of water is what causes even shallow water to be fantastically stable in temperature -- a lake that has more than couple tens of meters in depth is likely to be 4C at the bottom throughout the year whether it is frosty winter or hot summer above it, unless some kind of powerful event is able to mix the water in the lake.

Now, the small temperature differences will definitely have outsize effects on water circulation, ocean currents, life and weather. But I doubt they will cause meaningful sea rise unless somebody can calculate otherwise?

Not necessarily. The density of water peaks around 4ºC. So as oceans warm between 0º and 4º, they actually contract in volume.

This is untrue.

Ice is about 91% the density of water. If you have water at 0 height, and you put in water equivalent to +1 unit of height. If it's in liquid form, obviously height goes up by +1. If it's in ice form, there is +1.09 height worth of ice (because it expands when it freezes), but it only displaces water up to +1 unit of height in order to support its weight through buoyancy. The overall change in height is +1 unit regardless of whether it's liquid or ice

I could be wrong about this (it's been awhile since I took chemistry), but I think the ice has to be floating for the Archimedes principle to apply.

You can fill a glass of ice-water right up to the brim, and it won't spill over as the ice melts. But only if the ice is floating in the water. It's because the ice's mass pushes down on the liquid water, displacing a fixed amount relative to the weight of the ice.

Something I see a lot is people looking at worst case predictions as if they were presented as the most likely predictions. A lot of the IPCC reports say things like “if we continue to increase emissions, this will happen” (a worst case scenario) and also “if we make moderate improvements, this will happen” (a slightly better scenario). Then people who don’t want to talk about climate change mitigation will highlight the worst case scenario and say “see they were wrong and hysterical!” even when the moderate prediction, which they will ignore, ended up being essentially totally accurate.

Satellite data isn't that good unfortunately. Tide gauges say 1.5mm/year of rise, satellites say 3mm/yr, and they estimate satellite error to be +/- 0.5mm year, so the error bars are a significant fraction of the size of the overall change.

Also that assumes the scientists are completely accurate and don't make any mistakes. As recently as 5 years ago they discovered that the measured rise for almost all of the 90s was wrong and revised it by 3mm/year +- 1.7mm/year - the error was the same amount as the imputed level of rise!

This is no knock on the scientists, because measuring the height of a moving ocean from orbit to a level of accuracy that lets you see mm level changes is inevitably going to be very hard. But we should bear in mind that they're heavily biased towards wanting to believe the data is accurate. Their decade long inability to get the measurements correct didn't seem to have any impact on their confidence that they're currently getting it right, and why would it? Those who seize the data, seize the day.

Kind of a nitpick but glaciers are made of less dense fresh water compared to the salt water of the ocean. So melting glaciers will slightly increase sea levels.

Oh hey, what about the difference in density between fresh water and salt water?

https://nsidc.org/news-analyses/news-stories/melting-floatin...

Yeah, my comment was stupidly about how some other phenomenon doesn't exist.

But well, water being water, I imagine this doesn't happen at pressure; just for surface water. Is that the case?

The comment above says filling Qattara takes 1,213 cubic kilometres, which would mean about 3mm lower sea level. Which would be a real change, but also quite small in the bigger picture.

I guess depleting aquifers can lower land levels in those areas. I hear Jakarta has sunk 4 meters from that effect. But it's a separate thing from rising sea levels.

Yes. I've seen its tides in person. It's almost unreal. Boats go from sitting on their sides on dry land to floating in 3+m of water and back every tidal cycle.

Yes, and it is always COLD. (Newly engaged I took my fiancée to a beach west of Saint John and decided to go for a swim. I mean, I should have known better, I grew up there. It was a shallow slope, so by the time it was deep enough to dive in, I couldn’t feel my ankles. It was a short swim. It’s not like I was going to wimp out and turn back in front of my sweetie. Ah, the pride of youth.)

Re the tides: when Charles ame Diana visited NB in 1983, they disembarked at high tide in the Saint John harbour. The gangplank was at about 45 degrees, slopes down to the dock. A few hours later, it was 45 degrees down to the royal yacht. Some of the sailors, many of whom had long experience, having served in the falklands, among other places, had never seen anything like it.

There's even a waterfall that reverses direction based on the tides!

I mean, "plenty" isn't really true based on that link.

A best you could say "a few, in areas that are losing glaciers, which is expected due to basic physics"

That map clearly shows that only a few locations are experiencing a fall, so neither "plenty" nor summing to zero as claimed. But I'm interested to learn more about the evidence that the pre-industrial trend was the same, since my inexpert googling suggests otherwise, eg "Exceptionally stable preindustrial sea level inferred from the western Mediterranean Sea"

https://www.science.org/doi/10.1126/sciadv.abm6185