Summary: elevation estimates using data from SRTM [1] are too high in built-up areas, because unlike with LIDAR data it's not able to tell the difference between "this is high ground" and "this is low ground with a building on it". Which means many coastal urban areas are more vulnerable to sea level rise than people had previously estimated.

They try to get a better estimate by building a more complex model, and calibrate it using LIDAR where that's available. This lets them say not just "things are worse than we thought" but "these specific parts of these populated areas are at risk".

[1] https://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Missi...

Where does this fit in? https://news.ycombinator.com/item?id=21310972

If ice cliffs in the Antarctic won't collapse catastrophically that decreases our estimate for how quickly the sea is likely to rise, which is certainly good news!

But we're still going to get some rise, and accurate elevation modeling is important for figuring out what effects that's likely to have.

Roughly, you can think of these as two disconnected efforts: get the best estimate you can of the distribution of possible future sea levels, and get the best estimate you can of the impact of different sea levels on humanity. Your link is the former, this link is the latter.

It doesn't, this paper takes into account a wide error range in their analysis.

To put this in context we're talking about 4 to 5 mm per year of sea level rise on average globally for the next several decades.

Some areas will be more and some less as sea level rise isn't uniform (for instance isostatic rebound on the west coast of Canada will result in a net sea level drop in some areas).

Mitigation will be key as even if we eliminated carbon emissions completely today there's already committed warming in the system that will result in sea level rise through the century. We're just talking about how many extra mm per year on top of the 3-4mm or so that it is now.

The rise has been 3 mm a year (1/8 inch) since 1990 or about 4 inches.

http://sealevel.colorado.edu/

This has been averaging millions of measurements of satellite altimeter over oceans. That is considered more accurate than tidal gauges which are subject to local changes such subsidence near river mouths.

The 3 mm is a combination of land glacier melt and water thermal expansions. I have heard talks all over the map as to which factor is more dominant.

So 4-5 mm a year in the near future is not too off.

I liked table 1 as a nice summary from a referenced paper in the above paper, found here:

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014...

Their data suggests thermal expansion is the primary culprit.

Map of the rebound areas https://en.wikipedia.org/wiki/File:PGR_Paulson2007_Rate_of_L...

Mainly Canada and Fennoscandia.

Well, who knows what will happen in the areas with massive glacier melt? Earthquakes? Isostatic rebound of the under-glascier ground? Maybe some ground will lower.

Iceberg tsunamis too.

Definitely land rise. Whether or not that tends to be bound as lateral and subductive regions are, triggering earthquakes, isn't clear. My thought is that the risk is probablyl low, though impacts at/near subduction zones might be pronounced through induced earthquakes. A rising landmass (generally the over-riding plate) would tend to reduce the load on the oceanic (under-riding) plate, and allow stresses to be released.

Those earthquakes can be massive (Mag 9 Richter in Indonesia, Japan, and Chile), and induce tsunamis. In which case global warming could make for some major seismic events, but only in regions with existing faults.

The possibility of increased vulcanism has also been raised.

Here's a summary of the paper I gave before when a NYT piece covered it yesterday.

For USA and Australia, high-resolution/precision lidar-based maps are available of coastal areas. For other regions of the world it is not the case (or severely limited). However, gaining an insight into the elevation of land is crucial to determine a region's vulnerability to sea-level rise. NASA’s SRTM has almost global coverage of elevation levels, but is known to be too low resolution to be meaningful for this application (esp. in urban areas). A neural network was trained on the USA lidar data to augment the SRTM data (i.e. make the resolution higher). The network was verified on the Australian lidar dataset (and they got a good match; the model was already published elsewhere before [1]). The point of this paper was to then have the newly-derived elevation maps be exposed to sea-level change. This is where the maps with flooded cities come from [which were in the NYT article].

[1] https://www.sciencedirect.com/science/article/abs/pii/S00344...

Makes you wonder when coastal property prices start plummeting. And when banks stop granting mortgages for buying coastal homes. I don’t believe this is happening yet.

All else equal, being in an area susceptible to climate change related flooding lowers value about 7% on average according to some research:

https://www.axios.com/sea-level-rise-costing-billions-in-hom...

Is there a way to short these real estate investments and fleece climate-change-denying ideologues who are keeping coastal property values high? Do well by doing good! :D

If there was, you'd probably be paying a lot to hold the position for 30 years.

It's gonna happen over too long of a time horizon (from now, anyway) to profit handsomely off of. There are much better investments you can make today because they will pay off sooner.

Climate-change-denying ideologues like the Obamas? Or are you the one being duped?

https://www.google.com/amp/s/www.masslive.com/capecod/2019/0...

I'm surprised they still grant mortgages, a lot of coastal places can't get insurance anymore, a responsible lender wouldn't grant a mortgage on an un-insurable property.

Of course government can always mandate a head in the sand approach...

Then there's the mega wealthy that can always afford a new house anyway, they'll be happy to pay for the location.

Anyone know how insurance companies are reacting? That'd be interesting to watch, since they're all about risk management and have a lot of skin in the game.

Insurance is definitely the point to watch.

Real estate as investment makes sense only where the risk is insurable, and increasingly that's becoming less the case. If insurers won't insure, and banks can't get bailed out, mortgages won't get made, and property values will plummet.

A recent realisation of mine is that the so-called FIRE sector (apt name...), Finance, Insurance, and Real Estate, effectively tripods itself. Finance provides the liquidity, insurance assesses and socialises risks, and real estate provides a huge share of the actual backing assets. If any one leg of that tripod starts to weaken, the entire structure is at risk.

I ran across a pretty good explainer video from the WSJ yesterday on just this topic (or at least the "it's getting harder to insure" bits), mostly addressing California and wildfire, but also mentioning Florida and coastal storms.

https://invidio.us/watch?v=7X3FmFDOiDc

Looking for a good text treatment, that's not as easy to find at the moment.

Crossing their fingers for the next great bailout.

One thing I learned the average life of a 30 year mortgage is around 5 years. Everyone involved is passing the hot potato to the next sucker.

Oddly lots of rich and connected are buying coastal properties... You would think their financial advisors would prevent them even if the banks give no resistance

If they're rich, they can afford to experience prime real estate before it's erased forever and if they're connected, they can get a bailout afterwards.

They can afford to insure and rebuild homes in these areas.

They are not going to spend $ to rebuild - they'll have the government to bail them out.

This is very true.

Yeah so far coastal prices are far above the inland prices

Slightly unrelated, but first author on this paper is Scott Kulp, an acquaintance and fellow ACM member from my undergrad days, and above and beyond one of the smartest people I've ever met in my life. As in, double majored in Math and Comp Sci in undergrad, completing it in three years while looking dreadfully bored in every lecture we had together, smart.

Plug for thisplacewillbewater.com - they have a great map of what 4C warming will look like and you can also buy biodegradable stickers to post around and raise awareness if you live in an area that will be underwater.

Looks like SpaceX predicts <.5C rise given their Boca Chica launch site.

https://seeing.climatecentral.org/#12/25.9917/-97.1329?show=...

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

Or that they'll have more than one launch site in 20 years.

weird how sea level rise is always used as the doomsday scenario rather than the much more serious threat of delicate ecosystems collapsing and famine that would affect everyone.

this!

i'm finding that people - educated, thoughtful, caring people - have real trouble wrapping their heads around this threat, how serious it is, and how fast its coming.

these same people are very concerned about plastic pollution. real issue, but not civilization ending. and if we stopped the major sources tomorrow, we'd be fine. CO2 does not work this way.

i think it's because people can see and feel plastic. but they look out their window and things look...fine (apologies to california and other places where things are not fine)

> Over all, the research shows that countries should start preparing now for more citizens to relocate internally, according to Dina Ionesco of the International Organization for Migration, an intergovernmental group that coordinates action on migrants and development.

How the hell is Vietnam supposed to prepare for non-existence?

It doesn't have to? Look at a map of Vietnam, then look at the (relatively small) portion of Vietnam presented in the article's graphics...

A "relatively small" portion that's still a major territory loss that includes everything south of Ho Chi Min, and much of the city - of 10m. I'd say they have to. Perhaps quickly as these estimates appear to be based on RCP2.6 - that's the most optimistic track assuming everyone is meeting Paris goals. Right now, no one is.

Since the threat is so imminent, are there specific climate change predictions that have come true?

We’ve spent the last 15 years building better sewer systems all over Denmark in preparation for the increase in heavy rain falls due to climate change. We weren’t fast enough everywhere because the predictions proved conservative. Over all though it’s been a pretty big success.

Plenty, although "come true" depends on your definition, since the predictions are all very conservative, and the observations have tended to be worse than the predictions.

For example, the observations of the recent decline in sea ice are significantly worse than the models predict. [1]

Also, current data show the oceans are warming about 40% faster than predicted. [2]

[1] https://skepticalscience.com/graphics.php?g=35

[2] https://www.scientificamerican.com/article/oceans-are-warmin...

One of the predictions was that we'd get stronger heat waves in West Europe. We broke several old records this year. https://www.bbc.com/news/world-europe-49100271

But you've been in a warming trend for millennia in Western Europe -- the Danube and Rhine used to freeze over in the time of Tacitus.

The Danube and Rhine river froze over in times my parents can remember. A strong contributing factor to why rivers today don’t freeze any more is that we’re using them to cool power plants and similar.

They froze frequently, and this was not something noted in the 18th century, before power plants. You had reindeer in the Black Forest in Caesar's time. Europe was quite a bit colder in historical times.

The current temperature is clearly significantly hotter, and the rate of change is greater,

There has not been a "warming trend for millennia." The temperature rose steadily for about 1000 years since the Roman times, up through the Medieval Warm Period, then cooled steadily until about 1800, and then have shot up recently.

Take a look at the graph at https://en.wikipedia.org/wiki/Medieval_Warm_Period

We came out of a little ice age at around 1870. The causes are complex but include a huge amount of volcanic activity over 50 years potentially lower solar output during that time known as the Maunder Minimum. The effects of both on climate hung around but were effectively over by 1950 and we wouldn't expect any further warming since then.

The Maunder Minimum ended in 1715. Ice ages are not things that you "come out of" in a single year. Volcanic activity is not regular.

So your statement "over by 1950 and we wouldn't expect any further warming since then" has no basis.

You'll notice that I didn't we came out of it in a single year. I was saying that the factors that contributed to the Little Ice Age would have stopped having an influence by 1950.

Average temperatures are not that much higher yet. The specific prediction is that there will be more heat waves.

Warming trend vastly accelerated in a relatively short time frame to the point of the long term trend not holding much salience

The sea level has risen around 5-8 inches since 1900 and the rate at which it is rising has increased over the last several decades (and continues to increase). This is compared to roughly 2000 years of stable sea levels prior to the 1900's.

Exxon's 1982-vintage predictions on global temperatures have mostly held up.

https://earther.gizmodo.com/exxon-predicted-2019-s-ominous-c...

Interesting article. I thought everything was good until I hit that part

The only thing its scientists got wrong was that what they called “potentially serious climate problems” wouldn’t emerge until the late 21st century. So much for that.

The linked article refers to the loss in biodiversity, which is in my opinion not really related to climate change. It’s related to the fact that we humans leave less and less physical space for other species. I think it’s wrong to combine the two effects.

If trends keep going and warmer oceans finally kill off most of the coral reefs, there's your lost biodiversity right there.

One prediction: We will see large amounts of ice lost from the poles, seems to have been a good prediction.

The ones that have come true can pretty much be summed up by "shitty weather". Shitty weather is quite capable of wreaking havoc upon human food production and infrastructure though, so the future could be quite scary even if the more alarmist reports are exaggerated.

Did I just miss the link to the research material?

How much higher will it be? 6 inches? 2 feet?

I believe the paper is https://www.nature.com/articles/s41467-019-12808-z.

If I'm reading the paper correctly, the authors don't argue that sea levels will rise more than previously predicted. Rather, they argue that the classical technique for estimating impact by using elevation (SRTM) is overestimating elevation and therefore underestimating the impact of rising sea levels. The authors claim that their technique (CoastalDEM) also underestimates the impact of rising sea levels, but reduces the systemic bias present in previous estimates.

Thanks for the link. One statement from the paper: "this analysis assumes a static coastal topography".

This seems like a significant limitation, especially when a lot of the affected area consists of river deltas (eg, most of Bangladesh, the Mekong delta in Vietnam). One would expect that a rise in sea level in a delta would lead to increased silt deposition on the newly-submerged parts of the delta, reducing the impact compared to a naive calculation, perhaps quite significantly.

"Central estimates in the recent literature broadly agree that global mean sea level is likely to rise 20–30 cm by 2050 ref.3,4,5,6,7,8,9,10"

But what the paper is claiming, is that accepted methods of determining elevation are positively biased (estimates of land mass being higher than this new paper says):

"CoastalDEM reduces linear vertical bias from 4.71 m to less than 0.06 m."

At what point do we first see mass floodings from unusually high tides, such as during proxigean spring tide? Surely it must be soon if Veitnam will be underwater in just 30 years time?

Hurricane Sandy hit NYC during a spring tide, flooding downtown and knocking out power and a lot of subway tunnels. It cost 53 lives and about $19 billion.

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

Apparently it's already happened.

> The findings don’t have to spell the end of those areas. The new data shows that 110 million people already live in places that are below the high tide line, which Mr. Strauss attributes to protective measures like seawalls and other barriers.

So basically we have 110 millions of people living in "dangerous" areas so far yet nobody was impacted?

I don't know where you're getting no impact from, countries like Bangladesh are often being flooded (https://edition.cnn.com/2017/09/01/asia/bangladesh-south-asi...), in 1998 they had 68% of the country under water (https://en.wikipedia.org/wiki/Floods_in_Bangladesh). They are gradually getting more frequent and more severe, sooner or later they will be catastrophic.

There's plenty of places that are experiencing all sorts of problems with flooding. Look into Miami and Venice for starters; their problems are well-documented in English media. Less-developed cities are experiencing it worse, but aren't as well-documented in English.

If you include areas that are protected by seawalls and other barriers, I assume that number could include most parts of the Netherlands. Not exactly a helpful number. We should give priority to people who are currently unprotected.

Essentially, yes. The Dutch have been living with this for hundreds of years; it will cost, but it is certainly possible to construct mitigatory measures.

So the way it affects them is by requiring the expensive construction of seawalls, drainage and other defensive mechanisms.

They're affected by floods.

More than before? Where are the stats for that?

We've had cities and towns built in regular flood plains for thousands and thousands of years. Every single year there's a few weeks in the spring when the news is full of stories about snowmelt and ice dams or heavy spring rains causing massive flooding on the Mississippi and its tributaries.

is there any noticeable effect of earth’s rotation and uneven gravity field on distribution of sea-level change?

Yes gravity, and to a lesser extent rotation, have a (somewhat unintuitive) impact on how the sea level will change across different parts of the globe. There's a good overview of this topic here: https://www.theguardian.com/environment/ng-interactive/2018/...

Edit: video showing gravity changing over time due to melt: https://blogs.agu.org/wildwildscience/2016/07/21/gravity-gre...

The sea level as it stands today is already effected by gravity. And this is in fact built into the wgs84 datum. So vertical elevation is measured relative to that assumed sea level after the effects of gravity. And a rise in sea level would presumably be measured relative to that existing datum.

thanks!

nice video, seems like gibraltar is getting a lot of action

Does anyone have any sources for good projects for the USZ?

More? I can't think of one that's been erased yet.

Indonesia is moving Jakarta's capital status and government functions to a new city on Borneo. Of course, they cannot move Jakarta itself, which is also sinking due to groundwater extraction, and will be flooded unless they build a costly barrage system. They need to get the Dutch back to show them how (the Dutch will need a place to move anyway :)

Thailand is also discussing a similar plan to move the capital from Bangkok to Ayutthaya, the historical capital before the Burmese invasion of 1767.

New York is planning a sea wall system in southern Manhattan - The Big U - but what they really need is a truly BIG barrage from Long Island to Staten Island across the Narrows, and a smaller effort between the island and the New Jersey mainland. Closing the East River will be more difficult, depending on how much of the shoreline will be included. By coincidence, the Dutch also used to control New York.

More by 2050 i.e. more than previously predicted by 2050.

Any chance this gets published if it somehow found the opposite to be true?

To answer your conspiratory rhetorical question: Yes it would.

There are some good news from research reported, like "Slowdown in Antarctic mass loss from solid Earth and sea-level" feedbackshttps://science.sciencemag.org/content/364/6444/eaav7908

Just because there is less good news than bad news, does not make science biased.

I will disagree here, science usually is quite biased! There are always lines of thinking that get into fashion, where exaggerated claims are more common.

Climate change is one of those fields.

Everybody and their little sister want to be at the forefront, and they can only get there if they either claim to the savior or become that one special person that points out yet another imminent catastrophe. It is like a 11'o clock news, nothing but bad news to get people tune in.

Just to make sure, I want clearly state that I do believe that human-induced climate change is taking place. And that we should act, reducing waste, unnecessary air travel etc.

On the other hand, how many times do we read about that there could beneficial aspects to climate change? Right now I can't recall any instance. This is what I don't buy. Every change will suck for some, it might be better for others. Talking about anything positive in the context is taboo and it is part of the scientific bias that I believe is present. makes us all weaker because we can't quite prepare for something built on exaggerations and sensationalism.

We reward those that bring us bad news.

> To answer your conspiratory rhetorical question: Yes it would.

The accusatory tone of your response only reinforces my concern. It doesn't even require a "conspiracy" as you gibingly added. If a scientist considering publishing findings counter to consensus expects to be met with this kind of reaction from their peers, and shouts of "denier" at large, that's all it takes to put a finger on the scale to bias what gets published.

You protest too much and show your clear intent.

First, your "Any chance" question was clearly begging the question. The framing was that you believed the article wouldn't get published if it went the other way.

Then, when shown evidence that such articles do, in fact, get published, and that there is no conspiracy against them, you somehow suggest that... that response will keep scientists from publishing their work?

> a scientist considering publishing findings counter to consensus expects to be met with this kind of reaction from their peers,

They don't in climate science if their research is solid. Objectively bad research get shunned of course.

There is no basis for your suspicion.

Are you suggesting systematic bias in climate change publication? If so, would you like to point at any evidence that this is happening?

They had predicted almost a foot rise in sea level for 2020-25 in 1984. So we will see what happens. Source: https://books.google.com/books/about/Projecting_Future_Sea_L...