Why is sea level rise worse in some places?

https://nautil.us/why-is-sea-level-rise-worse-in-some-places-294325/

by rbanffy • 3 years ago

128 113 3 years ago

akeck2• 3 years ago

The affect of sea level rise on the Bay of Fundy is going to be... interesting.

mdjasper• 3 years ago

I just looked up The Bay of Fundy on Google maps, having not heard of it before. I'm interested, can you explain what about this particular bay will make it interesting?

ridgeguy• 3 years ago

Highest tidal range on the planet.

https://en.wikipedia.org/wiki/Bay_of_Fundy

timbit422• 3 years ago

Tom Scott at the Bay of Fundy: https://www.youtube.com/watch?v=nCrTsWtPVIY

jdontillman4• 3 years ago

(Largest tides on the planet. The bay acts as a kind of resonant organ pipe amplifying the tides on the Atlantic Ocean.)

Hey; if they can handle 52ft tides, they can handle anything.

wanderinghogan• 3 years ago

It's wild how locally variable the sea level surface is. I worked on a study that incorporated local sea levels into a bath-tub style sea level rise model that that also incorporated storm surge using ADCIRC modeling, and we tried to account for local land subsidence and uplift rates... anyways.

If you look at the "NOAA Tides and Currents" data, and go to Maryland, and click two points across the Chesapeake bay from each other. Go to More Data > Datum, you can see just across a 20 mile stretch of bay, Bishops Head MD MHHW (Mean Higher High Water, when there are two daily high tides, this is the elevation of the higher of the two) is 2.06 Feet over the vertical datum, while 20 miles away at Solomons Island MD it's a half foot lower, 1.48 Ft.

balderdash• 3 years ago

On a smaller body of water is that mostly wind?

rcme• 3 years ago

There are other factors, too. I remember reading about sea level change as a result of Greenland's ice melting. The sea level around Greenland is actually predicted to go down. One reason is that the ice is pushing the land down, and that effect will reverse as the ice melts. The other surprising reason is that the ice is massive enough to have a noticeable gravitational effect on the surrounding water.

https://www.theguardian.com/environment/ng-interactive/2018/...

HPsquared• 3 years ago

Seems we are missing "Land level rise" and "Land level fall". Those will be more patchy and local than sea level.

Cthulhu_• 3 years ago

Fun random factoid, big parts of Europe are still slowly rising because the weight of ice compressed a lot of it.

On the other side, a lot of land is sinking because the soil is drying out due to years of droughts and water mismanagement (farmers like to keep the water table lower. I live in NL where we have the water management infrastructure to tweak the water table)

arethuza2• 3 years ago

Post glacial rebound:

https://en.wikipedia.org/wiki/Post-glacial_rebound

ceejayoz• 3 years ago

On the other side, a lot of land is sinking because the soil is drying out due to years of droughts and water mismanagement...

Shockingly fast, too, in some spots.

https://www.nytimes.com/2021/05/25/us/corcoran-california-si...

"Over the past 14 years, the town has sunk as much as 11.5 feet in some places..."

morkalork• 3 years ago

Same thing happened in Vermont with some of the evidence for it being whale skeletons found in fields hundreds of miles from the ocean: https://en.wikipedia.org/wiki/Charlotte_whale

GrumpyNl• 3 years ago

When the soil is drying out, it will start to float. Im from Boskoop in NL, we have that problem with peat soil (veen grond). This is also irreversible, when peat soil gets dried it will not become wet again.

tannhaeuser• 3 years ago

That's exactly what TFA is explaining.

tonmoy• 3 years ago

This is literally two of the three things the article talks about.

ohdearno3• 3 years ago

Yeah, and that's good locally, but globally we see a rise overall.

luckylion• 3 years ago

Are the Qattara Depression project and similar proposals too small in impact or more expensive than building better flood management, or why aren't we doing those?

thombat3• 3 years ago

Much too small. Using Wikipedia's figures: volume of Qattara Depression = 1,213 cubic kilometres, volume of Greenland ice sheet = 2,850,000 cubic kilometres. And the project is only useful as a long-term power source if the contents evaporate leaving space for renewed inflow, i.e. it only sequesters a fraction of its volume.

BurningFrog3• 3 years ago

Making Qattara a bay of the Mediterranean would be great as a way to bring life and human habitation to the desert.

It's incredibly expensive though.

Scott Alexander estimated it would "reverse one year worth of global-warming induced sea-level rise" here: https://slatestarcodex.com/2016/04/15/links-416-they-cant-li...

hinkley3• 3 years ago

There are 360 million square kilometers of ocean. Of course sea level rise increases the surface area a bit but if you assume 1 mm (1 millionth of a kilometer) goes straight up then each mm of sealevel is 360 cubic kilometers of water.

We are depleting our aquifers at a rate of about 280 km^3 per year. US is down over 1000 km^3 since ~1900. I'm not sure how much of that ends up in the ocean, but reducing that number and taking it negative would go a long way toward slowing sea level rise.

BigCryo• 3 years ago

Because overall it has not risen at all?

thombat3• 3 years ago

For that to be true there would be plenty of places where it's falling. Are there?

flavius29663• 3 years ago

there absolutely are, a google away https://tidesandcurrents.noaa.gov/sltrends/

But they are generally rising, just not more than compared with pre-industrial era.

ohdearno3• 3 years ago

It's risen ~97mm since 1993. The rate of increase in that rise has been increasing steadily since ~1993. The consistency of our data has also been much better since then (previously it was only the highly noisy coastal tide gauge data).

Fun fact: the slowest its been in the last century was when we did a crap-ton of dam projects in the 50s-70s, still rose, but very little.

consumer451• 3 years ago

Last I looked at the data, sea levels in Key West had risen by around one foot in the last hundred years.

lapama• 3 years ago

Because in the long term the world does not act like a glass of water: there are currents and gravity.

jdontillman4• 3 years ago

The NOAA Sea Level Trends data and visualizations are fascinating:

https://tidesandcurrents.noaa.gov/sltrends/

Sea levels have been monitored for over 100 years... because of commerce.

East coast US seems to be going up about 3mm/year, or a foot per century. That's on top of 7 foot tides.

West coast US is very steady, barely moving at all.

The sea level is dropping in Alaska by 10mm/year. Dropping in Scandinavia also.

Some cities show rising sea levels, but really the cities are sinking due to collapsing aquifers; New Orleans and Bangkok. And measurements made on river deltas are always going to be wild due to silt and all.

Most notably, I can't find an example in the NOAA data of the rate of sea level rise increasing due to industrialization. Anybody?

arethuza2• 3 years ago

Isn't that relative sea level changes in places like Scandinavia - the sea isn't dropping, the land is rising?

https://en.wikipedia.org/wiki/Relative_sea_level

jdontillman4• 3 years ago

Exactly.

Because the sensors are mounted on that very land.

So tectonic movement will certainly have an effect. And you can see remnants of earthquakes in some of the data.

BurningFrog3• 3 years ago

Yeah, the sea must be "level" in some sense across the planet.

Don't know if local variations in gravity may have a measurable impact?

twawaaay3• 3 years ago

There is only one reason the sea can rise currently due to weather and that is glaciers getting melted.

Another reason (but not due to weather) is that when land somewhere goes up, it will displace water everywhere else. And so, for example, if the land is still recovering from the ice age we should see ocean levels going up everywhere except for the pieces of land that are recovering from the weight of the glacier that is no longer there.

Mind that Arctic is not causing sea level rise. Any ice that is floating on water will not cause any water level change when it melts. (I know this is somewhat unintuitive but it comes directly from Archimedes principle)

So we are talking basically Antarctic ice and Greenland because these are by far the largest bodies of frozen water that are supported by land rather than floating on the ocean.

I think it should be pretty easy to observe how much of that water melted or slipped into the sea.

I also think that currently, coastal erosion is mostly caused by changing weather patterns. Basically this comes down to wind blowing in different directions, speed and variety and these changing patterns mean coasts are eroding in different places than before.

locopati• 3 years ago

Also, warming oceans causes expansion which causes sea level rise.

https://www.jpl.nasa.gov/edu/learn/project/how-warming-water....

trompetenaccoun• 3 years ago

No, it's not just due to weather (you probably mean climate anyway). For example, ice melting in one place, say Antarctica, will affect sea levels elsewhere on the planet because of weaker gravitational forces where the ice used to be. Geoscience is complex and measuring changes on such a global scale is not "pretty easy", even if it's only sea level changes. It's nothing like a bathtub or elementary school physics.

Not to rant but this is one of those threads again. The majority of comments contain misinformation.

withinboredom2• 3 years ago

Umm. I’m pretty sure if water that exists above the water line is melted into the water line, the overall water line will rise. You can directly observe this in a glass of ice that starts with no liquid water will melt into a glass of liquid water.

martinpw• 3 years ago

Most notably, I can't find an example in the NOAA data of the rate of sea level rise increasing due to industrialization. Anybody?

You can look at the graph on the NOAA site here and see the acceleration visually: https://www.climate.gov/news-features/understanding-climate/...

The notes to the left of the table say 1.4mm/yr for much of 20th Century to 3.6mm/yr now.

There is also evidence of acceleration of sea level rise just from satellite data, 0.08mm/y^2:

https://www.sciencedaily.com/releases/2018/02/180212150739.h...

Trumpi2• 3 years ago

Back in 2006, our expectations were set when An Inconveient Truth contemplated what would happen if sea levels rose by six meters (in our lifetime). 3.6mm a year seems a bit meh in that context.

mc32• 3 years ago

I think the arctic region is affected by glacial rebound: the ground slowly recovers from past glacial compression.

Subsidence is a thing in Silicon Valley. San Jose has sunk some feet since the aquifer was drawn, fist for agriculture and now urbanization.

WillPostForFood• 3 years ago

We shouldn't be calling subsidence sea level rise. They are two distinct, measurable, phenomena that happen to have the same impact.

sp332• 3 years ago

I don't think it was possible to measure them separately until we had good satellite data from the last two decades. If we're extending trends back to the beginning of the industrial revolution, they're going to be mixed.

amelius• 3 years ago

What I wonder about is: rising wrt. what? Did they take into the account the possibly vertical movement of tectonic plates?

revelio5• 3 years ago

They do take that into account. They calculate that the ocean floor is sinking but then ADD that displacement to their reported measurement of "sea level", which is backwards. When the ocean floor sinks sea level goes down, but they report it as going up instead, using this justification:

https://sealevel.colorado.edu/index.php/presentation/what-gl...

currently some land surfaces are rising and some ocean bottoms are falling relative to the center of the Earth (the center of the reference frame of the satellite altimeter).

since the ocean basins are getting larger due to GIA, this will reduce by a very small amount the relative sea level rise that is seen along the coasts.

We apply a correction for GIA because we want our sea level time series to reflect purely oceanographic phenomena. In essence, we would like our GMSL time series to be a proxy for ocean water volume changes. This is what is needed for comparisons to global climate models, for example

This is nonsense, of course. Volume isn't measured in millimeters, that's a measurement of distance. GMSL when talking about satellites is defined as the average distance of the surface of the ocean from the center of the Earth, and the reason people care about it is because if it gets too high then things we care about end up flooded. Changing the definition of GMSL half way through from sea level to sea depth is the kind of slippyness that pervades this space.

margalabargala• 3 years ago

East coast US seems to be going up about 3mm/year, or a foot per century. That's on top of 7 foot tides.

That's the average rise it you average all data going back to the 1950s.

Unfortunately, looking back to the 50s is only really useful if interested in how much sea levels have already risen. Otherwise it presents an unrealistically optimistic view, as the rate has accelerated since.

Per the article, the east coast (North Carolina) is currently experiencing an increase of about a third of an inch per year, which is an increase of one foot per 36 years, or close to a meter per century.

If current trends continue, this will accelerate, not decelerate.

jessewmc• 3 years ago

Your unit mixtures hurt my brain

spacetime_cmplx4• 3 years ago

I have two related questions:

1. Global temperature is rising. Any water that used to be above 4°C (or the equivalent for salt water) now takes more volume. But what about water that's below 4°C? Wouldn't that water compress? What portion of the ocean is colder than 4°C? I'd imagine all of the Arctic zone and near Antarctica is, which is an awful lot of water to offset the tropical water. An even more nuanced perspective would be to look at the actual temperature distribution and use it to weight the dV/dT of water at different temperatures.

2. Global temperature is rising. Ice is melting into water. This is new mass entering the ocean. Why can't the sea bed, which is under more pressure due to extra mass, expand? The sea bed isn't a steel utensil, it's sand and rocks. And it's constantly shifting. And it's composition is different in different regions.

Has anyone done a detailed computer simulation of the whole earth's geology under rising temperatures? There might be feedback loops that might amplify or negate some effects so it's quite important to account for all variables. And obviously there's a lot of variables to account for.

(It's sometimes scary how little we know about our own planet. I'm not talking about the things in my comment because I'm sure it's just my ignorance.)

Timon3• 3 years ago

1. Global temperature is rising. Any water that used to be above 4°C (or the equivalent for salt water) now takes more volume. But what about water that's below 4°C? Wouldn't that water compress?

It might marginally, but the amount of water compressed will be a lot smaller than the amount of water "uncompressed", both due to the larger range of temperatures above 4°C (below is only a bit, and then ice) and due to the fact that the densest water is at the bottom, meaning that it's easier for everything else to heat up.

2. Global temperature is rising. Ice is melting into water. This is new mass entering the ocean. Why can't the sea bed, which is under more pressure due to extra mass, expand?

Expand where? It can't just rise since there is gravity, and the pressure above increases with more water. It can't go down because there is already other stuff there.

friend_and_foe• 3 years ago

In regard to that last point, I hadn't thought of it but there is something called post-glacial rebound, it would make sense that the increased weight on the seabed would deform it, and potentially even cause bulging of land without ocean on top, potentially negating the sea level rise effect to varying degrees worldwide.

spacetime_cmplx4• 3 years ago

Expand where?

Think of the ocean bed as a trampoline. Obviously much more rigid, but that's the image in my head.

It can't go down because there is already other stuff there.

Why not? Rocks and sand can be compressed with sufficient pressure.

marcosdumay2• 3 years ago

Wouldn't that water compress?

You say it because of the extra volume on top of it?

If that's the case, not because of heating. The volume increases, the water still weights the same.

spacetime_cmplx4• 3 years ago

No, water is most dense at 4°C. If you take water at 2°C and increase its temperature by a degree, it will _compress_, not expand. But if you take water at 10°C and heat it by a degree it will expand. My question is what percentage of the expansion is offset by the compression.

(Note that the 4°C number is only for pure water.)

water still weights the same

Weight has nothing to do with my first point. It's the increase in volume that spills into land.

slackfan• 3 years ago

Reminder that Ice takes up more volume than water.

spacetime_cmplx4• 3 years ago

I know, did I say otherwise anywhere?

adgjlsfhk12• 3 years ago

the key point is that there is very little water below 4 Celsius because it would rise into warmer water and heat up.

irrational• 3 years ago

One is that the ocean is warming, and it needs more space and expands.

That doesn’t sound right. I think it is common knowledge that water expands as it freezes (hence, burst pipes), not when it warms up.

giraffe_lady• 3 years ago

That's just a quirk of ice, that it's lower density than water. Liquid water still does what most (all?) liquids do wrt temperature changes.

justsocrateasin2• 3 years ago

Water density is almost fully inelastic w/rt temperature. At 60°F the density is 0.99907 g/cm^3, at 100°F the density is 0.99318 g/cm^3. I think that's something like a .5-1% change in density. Pipes bursting is purely because of the drastic density change from ice crystallization.

https://www.usgs.gov/special-topics/water-science-school/sci...

kybernetikos2• 3 years ago

Water is at its most dense around 4 degrees C. As the temperature increases from there it gets less dense.

mcguire2• 3 years ago

The thermal expansion coefficient of water: https://www.engineeringtoolbox.com/water-density-specific-we...

nomel• 3 years ago

No expert, but here's what I found, because I was curious too.

Ice in water doesn't change the waters height. If you put an ice cube in a cup, the water will be the same height after the ice has melted [1], since the "excess" is lifted out of the water. For some numbers, in 2020, it looks like total sea ice peaked at 18,785 km3, with the oceans volume being 130,000,000, so 0.014% [2].

The thermal expansion of water, as liquid form, is going to be much more important [3].

Related, every time I try to look into climate numbers, I get the sense that there's a gap between grade school explanations and research papers. There's not much between. Asking ChatGPT just reinforces this view. It treats me like a kid, or wraps unsolicited disclaimers/summaries around everything.

1. https://physics.stackexchange.com/questions/110645/why-does-...

2. https://arctic.noaa.gov/Report-Card/Report-Card-2020/ArtMID/...

3 https://physics.stackexchange.com/questions/506759/how-much-...

justsocrateasin2• 3 years ago

Seeing a lot of people talk about how the density of water is going to change with a temperature change. I don't really think that's true. Liquid water density is pretty darn inelastic and almost fully incompressible. It's one of the reasons hydraulics works. Ice on the other hand has a pretty different density.

Water density table - https://www.usgs.gov/special-topics/water-science-school/sci...

If the temperature of the ocean changed by 10°F that would result in a .1% change in overall volume. Obviously that does make a difference because the ocean is so big, but it's a lot less consequential than ice, which is above the water, melting into the water and ice.

kybernetikos2• 3 years ago

But if the ice is floating, it should displace the same volume of water that it will melt into.

nemo44x• 3 years ago

It's amazing how many people don't understand this. It displaces the same amount of water whether it is frozen and floating or melted. Easily tested by filling a glass with water and adding an ice cube and then drawing a line at the water level and letting the ice melt. The water level will be the same.

Of course, if the ice is on land and melting into the ocean, that's different.

donatj• 3 years ago

If we look at the global picture, there are two major reasons why sea levels are rising. One is that the ocean is warming, and it needs more space and expands.

My understanding is that water expands quite a bit less in the range between 32°F and 212°F than it does when it freezes.

It seems like floating ice melting and decreasing in volume 9% is notably more significant than the volume increase from a couple degree temperature increase. There also certainly way more liquid water than solid to contend with.

I'd be curious to know the effect of melting ice decreasing the volume versus the temperature rising increasing the volume.

stochtastic6• 3 years ago

Archimedes would like a word. There are some small effects due mostly to salinity differences, but sea ice isn't a major contributor because it is already floating and thus displacing an equivalent volume of water:

https://en.wikipedia.org/wiki/Sea_level_rise#cite_ref-113

hinkley3• 3 years ago

Sea ice also reflects light. Remove the ice and the water beneath heats up.

That's part of the runaway effect we are freaked out about.

WeylandYutani• 3 years ago

The Netherlands is also sinking so you get a double whammy.

stochtastic6• 3 years ago

This article only briefly touches on what I think is the most interesting aspect of sea level rise: gravitational adjustment. Even though I never worked seriously on sea level research, it was by far my favorite course in graduate school. For anyone who would like to learn more, I highly recommend listening to Jerry Mitrovica expound on the subject [1]. I guarantee that you will learn a few things that will stick with you.

In my experience, the first order adjustment effects are not widely known even among physical oceanographers. I remember describing it to a preeminent expert on El Nino, and him being incredulous that local sea level fall near the source of meltwater could be the first-order effect beyond accounting for rebound. "The first-order response is a Kelvin wave — you've surely been misinformed."

[1] - One example lecture: https://www.youtube.com/watch?v=s_rGksRoG9A

[2] - Another, shorter summary talk https://www.youtube.com/watch?v=yj7JIxU9Af4

PM_me_your_math• 3 years ago

Great, now we need to raise taxes to stop tectonic plates.

Why is sea level rise worse in some places?

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