Rising Seas Will Erase More Cities by 2050, New Research Shows

[jefftk]

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...

[GrumpyNl]

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

[poutine]

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.

[peter303]

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.

[nabla9]

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

Mainly Canada and Fennoscandia.

[itcrowd]

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...

[wsc981]

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.

[peacetreefrog]

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...

[rectang]

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

[flukus]

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.

[Reedx]

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.

[Gibbon1]

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.

[GenerocUsername]

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

[shams93]

Yeah so far coastal prices are far above the inland prices

[auto]

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.

[seveneightn9ne]

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.

[adolph]

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

[leeoniya]

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.

[shawnb576]

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)

[pmiller2]

> 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?

[sithadmin]

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...

[yters]

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

[moksly]

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.

[SamBam]

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...

[lurker458]

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

[standardUser]

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.

[roywiggins]

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

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

[Angostura]

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

[ahje]

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.

[brohoolio]

Did I just miss the link to the research material?

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

[luu]

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.

[listenallyall]

"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."

[steve19]

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?

[comicjk]

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_...

[catalogia]

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.

[keymone]

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

[chris_overseas]

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...

[klyrs]

https://www.nature.com/articles/s41467-019-12808-z

[arkades]

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

[IanDrake]

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

[mikhailfranco]

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.

[asah]

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

[tengbretson]

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

[ycombonator]

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...