Naked Science Forum
General Science => Question of the Week => Topic started by: Adam Murphy on 18/11/2019 17:46:25
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Geoff wants to know:
"How is it that there are rising sea levels impacting some island nations such as the Maldives and Kiribati, yet 1000 kilometres in any direction there is no discernible sea level change at all?"
What do you think?
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How is it that there are rising sea levels impacting some island nations such as the Maldives and Kiribati, yet 1000 kilometres in any direction there is no discernible sea level change at all?"
I've not seen any data on this. Sea level has risen about 1/6 meter in the 20th century, everywhere. These nations are at risk from a ~2 meter sea level rise (barring curbing of emissions) predicted for the 21st century since they've no high ground to which they can retreat. Netherlands is already below sea level, but they can only build their walls so high.
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On the open sea it hardly matters how deep the ocean is. 1263 meters is identical to 1263.8 meters for all intents and purposes. But if you live on an island that rises 1263.5 meters from the bottom of the ocean, that difference is very big! (the difference between a parking lot and a beach.)
Small islands and costal areas with very small slopes are at the greatest risk from rising sea levels. A change of only a few centimeters in the average sea level can effectively steal seaside real estate. (see Venice: https://www.bbc.com/news/world-europe-50401308, and The Eastern Seaboard of the US: https://www.phillymag.com/news/2019/07/11/atlantic-city-flooding/)
Another aspect of climate change that can raise sea levels locally, is more intense storm surges. There is a predicted trend (and it seems to be holding up) that major storms will become more powerful, and have lower and lower air pressures and stronger and stronger winds. The lower the pressure of a storm, the higher the water will rise underneath, and the stronger the winds, the more the water will pile up against the shore.
http://www.hurricanescience.org/society/impacts/stormsurge/
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Sea level is not actually a meaningful parameter. The solid crust rises and falls at various spots.
Various historic ports are now several miles inland, whilst whole towns have disappeared under the waves. Consider for example the north Norfolk coast, where once-thriving saltwater ports like Cley are now a mile from the coast, just 100 miles from the Suffolk coast where half of Dunwich has disappeared under the North Sea in the same period.
Coral islands are very attractive but only exist because the sea level used to be higher - coral doesn't grow in air.
Venice is mostly artificial, landfill between piles. The piles have been sinking since they were built. Sic transit gloria etc.
Meanwhile volcanic islands appear from time to time between Scotland and Iceland, as well as along the Pacific ridge.
It all depends on your arbitrary datum.
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From another chapter of Randall Monroe's "How To..." book:
If you succeeded in melting the Greenland ice shelf (in isolation), the sea level of Greenland would not rise.
- This is because the ice pack exerts a gravitational attraction on the nearby ocean, thus raising the sea level around Greenland.
- Spread the water from the Greenland ice shelf evenly around the world, and this gravitational attraction is gone, and the sea level around Greenland drops.
- His suggestion was melt an ice-shelf on the opposite side of the world from where you wanted the sea level to rise...
- Of course, ice pack melt in Greenland is mirrored by ice-pack melt in Antarctica, so there is some sea-level rise around the world.
Some research into human migrations into North America identified an island off Canada where they believe that the effects of melting ice and rising sea level would have almost canceled, leaving an island with stable sea-level that should preserve artifacts roughly where they were left (and not submerged and battered by the sea).
There are other effects at play, for example, during the last ice age, Scotland was covered by a thick ice sheet. That melted perhaps 10,000 years ago. The rock under Scotland is now (slowly) rebounding, and rising out of the sea. However, the UK is now moving like a "see-saw"/"teeter-totter", pushing London down faster.
And then there are areas like the Mississippi basin, which is a subduction zone, and would be descending below sea level, even if it weren't for sea-level rise. Build up levees to block the regular flooding and deposition of silt to build up the land, and you set the scene for even more flooding.
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However, the UK is now moving like a "see-saw"/"teeter-totter", pushing London down faster.
It's also tilting west-east, with Cornwall rising and Kent dropping. The Ordnance Survey datum is a mark on the harbour wall at Newlyn (Cornwall) so in fact sea level is falling.
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Thank-you for all the responses.
We also have an answer from Dr. Rob Larter of the British Antarctic Survey, which you can find in the "Print me a new liver!" podcast.
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Atolls are eroded volcanoes that are gradually collapsing with minor earthquakes, so sea level rise is replacable with landmass sinking
https://en.m.wikipedia.org/wiki/Atoll
The glacial rebound of northern landmasses is contributing to sea level rise, parts of norway are being left high and dry if the slopes are not steep enough. Southerly landmasses sink and are doubly hit by the increaced displacement of water.
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It's worth noting that almost the whole of Australia's desert regions used to be a seabed. Humans are a mere glitch in the evolution of the planet, and our discomfort is of no global consequence.
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It's worth noting that almost the whole of Australia's desert regions used to be a seabed. Humans are a mere glitch in the evolution of the planet, and our discomfort is of no global consequence.
The very existence of our planet is a mere glitch in the evolution of the galaxy, and our solar system is of no galactic consequence. So what?
We are people, who live and experience on a human timescale of decades, and are part of a complex civilization that operates on a timescale of centuries. The issue of climate change is driven by the relevance of human choices that influence human experiences and societal choices that influence the course of geopolitical history. Please stop the Nihilism of "the world has been and will be ever changing" Yeah, we know. I want my life to be better in 20 years than it is now, not worse. I want my society's economy and social currency to be more valuable, not less. I want my descendents to have better lives than my own, not worse. I have some modicum of control over my influence on the climate, and hope to influence our civilization for the better.... Sheesh!
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All very laudable, and the answer is simple
1.If you live near a sinking coast, move inland
2. Burn all the fossil fuel while it lasts, before someone else does, and invest part of it in a future sustainable source with good storage
3. Persuade everyone else to let you do this
4. Persuade everyone else to reproduce below the replacement rate for about 100 years
There is no point in waiting for governmental or intergovernmental action on mitigating the effects of climate change. Any such action is a vote loser apart from 4, which requires more intelligence than any politician possesses.
Sadly, the more I think about this subject, the more I am led towards survivalism.