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Our Burning Planet

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Our Burning Planet

Think twice before buying a property on the beach – Sea level is rising

The ever-restless sea follows the movements of the moon and sun. It’s shaped by the wind into great swells and troughs. And it stacks up on east coasts by inertia from the spin of the Earth. Sea level might seem like a moving target, but it is precisely measured in millimetres. 
Think twice before buying a property on the beach – Sea level is rising Right now, we know that sea level is rising. Different sets of instruments, plus record-keeping going back over 100 years, indicate that between 1880 and 2014, the average global sea level rose by around 20 centimetres. And it’s speeding up.  Read more in Daily Maverick: Rising seas, sinking shores - how the V&A Waterfront is bracing for impact  During the 20th century there was an increase in average global sea level of around three millimetres a year. In 1993 it was 4.6 millimetres. NASA estimates that, at this rate, the sea level could be about 30cm above today’s level by 2050. It may not seem much, but in a storm surge, that amount of extra water across an entire coastline is huge. The driver of the rising sea level is increased global temperature. As heat from the atmosphere is transferred into the oceans, the water warms and expands, increasing the oceans’ volume and causing it to rise. Raised temperatures also mean increased melting of land-based ice such as glaciers and ice sheets. As they melt, more water enters the ocean – and sea level rises.  The measurements of these changes are vital indicators of how the planet is faring as it heats up. An ever-rising sea could spell disaster for coastal cities and low-lying islands in the future. Being that the sea is an ever-moving thing that’s seldom the same level as it was seconds before, how can measurements be so precise? There are no fewer than five ways: floats, pressure gauges, sound, radar and satellites. [caption id="attachment_2326035" align="alignnone" width="795"]sea levels A radar tide gauge. (Photo: UNESCO)[/caption] A float in a still pipe or well rises and falls with the tide and records these changes on a paper chart. It was the original means of measurement and is how most historical records were made. [caption id="attachment_2326034" align="alignnone" width="376"]sea levels A pressure sensor gauge. (Photo: UNESCO)[/caption] Pressure-based gauges measure the pressure on a water column which is proportional to the water depth, averaging the rises and falls over time. Acoustic gauges use bounced sound waves to the water surface from below, and land or satellite radar uses microwave reflections to measure the average level from above. The aim is to filter out wind, wave and tide movements from the sea’s eternal restlessness. Where to place land-based gauges requires a lot of thought. They need to be tough enough to withstand storms and be on stable ground, away from river estuaries that can raise water levels and headlands or shipping that cause turbulence, and need a constant supply of electricity. [caption id="attachment_2326036" align="alignnone" width="796"]sea levels An acoustic tide gauge. (Photo: UNESCO)[/caption] [caption id="attachment_2326032" align="alignnone" width="667"]sea levels A GPS buoy used in sea level calculations. (Photo: UNESCO)[/caption] [caption id="attachment_2326037" align="alignnone" width="431"]sea levels Measuring sea level from groups of satellites. (Photo: UNESCO)[/caption] Using more than 100 years of measurements, hundreds of measuring stations, global collaboration and the ability of artificial intelligence to crunch data sets, the conclusion is definitive: the sea level is rising and it’s accelerating. If you’re planning to invest in a coastal property within the sound of the waves as a retirement option, you might be giving a headache to any family member who inherits it. DM https://www.youtube.com/watch?v=REeWvTRUpMk
Don Pinnock
By Don Pinnock
22 Aug 2024
Facebook
32

Right now, we know that sea level is rising. Different sets of instruments, plus record-keeping going back over 100 years, indicate that between 1880 and 2014, the average global sea level rose by around 20 centimetres. And it’s speeding up. 

Read more in Daily Maverick: Rising seas, sinking shores - how the V&A Waterfront is bracing for impact 

During the 20th century there was an increase in average global sea level of around three millimetres a year. In 1993 it was 4.6 millimetres. NASA estimates that, at this rate, the sea level could be about 30cm above today’s level by 2050. It may not seem much, but in a storm surge, that amount of extra water across an entire coastline is huge.

The driver of the rising sea level is increased global temperature. As heat from the atmosphere is transferred into the oceans, the water warms and expands, increasing the oceans’ volume and causing it to rise. Raised temperatures also mean increased melting of land-based ice such as glaciers and ice sheets. As they melt, more water enters the ocean – and sea level rises. 

The measurements of these changes are vital indicators of how the planet is faring as it heats up. An ever-rising sea could spell disaster for coastal cities and low-lying islands in the future.

Being that the sea is an ever-moving thing that’s seldom the same level as it was seconds before, how can measurements be so precise? There are no fewer than five ways: floats, pressure gauges, sound, radar and satellites.

sea levels A radar tide gauge. (Photo: UNESCO)



A float in a still pipe or well rises and falls with the tide and records these changes on a paper chart. It was the original means of measurement and is how most historical records were made.

sea levels A pressure sensor gauge. (Photo: UNESCO)



Pressure-based gauges measure the pressure on a water column which is proportional to the water depth, averaging the rises and falls over time. Acoustic gauges use bounced sound waves to the water surface from below, and land or satellite radar uses microwave reflections to measure the average level from above.

The aim is to filter out wind, wave and tide movements from the sea’s eternal restlessness. Where to place land-based gauges requires a lot of thought. They need to be tough enough to withstand storms and be on stable ground, away from river estuaries that can raise water levels and headlands or shipping that cause turbulence, and need a constant supply of electricity.

sea levels An acoustic tide gauge. (Photo: UNESCO)



sea levels A GPS buoy used in sea level calculations. (Photo: UNESCO)



sea levels Measuring sea level from groups of satellites. (Photo: UNESCO)



Using more than 100 years of measurements, hundreds of measuring stations, global collaboration and the ability of artificial intelligence to crunch data sets, the conclusion is definitive: the sea level is rising and it’s accelerating.

If you’re planning to invest in a coastal property within the sound of the waves as a retirement option, you might be giving a headache to any family member who inherits it. DM

https://www.youtube.com/watch?v=REeWvTRUpMk

Comments

Henri Lombard Aug 23, 2024, 07:30 AM

So in 134 years sea level has gone up 20 cm - that equates to 15 cm in the last century. Well I'm surely not going to worry about leaving a home to my kids if it happens to be located near the beach. In their lifetime it may well rise some 5, 10 or 20 cm but will this affect the property? No!

MT Wessels Aug 23, 2024, 10:05 AM

Some nuance is required. Much depends on the slope of the coastline and the material (sand vs rock). 20o mm vertical may not appear to be much, but it could mean 3 - 5m further ingress over land - including erosion and exponential flood line expansion.

Henri Lombard Aug 23, 2024, 11:17 AM

I agree with your comment. Mathematically it's valid but having walked the beaches of SA over the past 70 or so years, I can't think of any areas where such a situation will arise. Perhaps you could suggest an area that I may not be aware of.

Bruce Sobey Aug 23, 2024, 07:16 PM

Go to Ballito. The old toilets are packed up with sandbags and new temporary ones have been built at a higher level. The newly repaired road was also damaged. It is a combination of erosion and sea level rise. The old Durban Dunlop was getting flooding problems during a high tide and rain storm.

Arnold O Managra Aug 23, 2024, 11:47 PM

There are many effects in play here, Bruce. Ballito was a steep beach even before the massive development. Human interference - piers etc. impacts natural sand movement, which is critical to both surf breaks and "health" of normal beach. It's not "climate catastrophe", it's human impact.

Johan Buys Aug 24, 2024, 07:54 PM

Henri: If you look at low slope beaches it is very visible. So langebaan beach for example. Low tide mark now is linearly 30m closer to the Main road. Many homes now have 8 brick walls to keep high tide away, and that is a lagoon with little reach effect from storms at wrong time.

superjase Aug 23, 2024, 11:36 AM

it will affect the storm surges mostly. large storms would now have that extra little bit needed to cause serious flooding. and the incidents of flooding will occur far more frequently. also, it affects erosion rates.

superjase Aug 23, 2024, 11:37 AM

i'll be sure to remember that once i am wealthy enough to purchase a beachfron property.

megapode Aug 23, 2024, 03:06 PM

And that will be OK most of the time. But when there's a big storm or a spring tide, then things may get uncomfortably close.

Arnold O Managra Aug 23, 2024, 03:23 PM

In addition, pretty much all of the coastal property under discussion was built in the last 100 years. Unless society collapses completely, in which case housing will collapse anyhow, it seems unlikely that we will simply sit and watch. 20 metres seems worrying, even over a century, but 20cm? Meh

Marianne McKay Aug 24, 2024, 08:38 AM

That's 20cm depth increase all over the world, not 20cm washing horizontally up the beach...

Arnold O Managra Aug 24, 2024, 10:22 AM

I understand 20cm in a century vertically. That's 2mm vertical per year. My point was that if 99% of the endangered coastal buildings were built in the previous century, then it seems odd that nothing similar would occur in the following century. For example protecting existing infrastructure.

Malcolm McManus Aug 23, 2024, 08:02 AM

I wonder if isostatic rebound affects sea level lowering.

MT Wessels Aug 23, 2024, 10:37 PM

No GIA at 34 degrees latitude (Cape Town furthest south); mostly confined to far northern hemisphere (Norway, Sweden, Iceland, Alaska, Greenland).

Roux Joubert Aug 23, 2024, 08:56 AM

You forgot to add a title

Roux Joubert Aug 23, 2024, 08:56 AM

You forgot to add a title

johnbpatson Aug 23, 2024, 09:43 AM

Yip, but it is usually not the coastal towns which suffer. A lot of the the flooding inland is due to rain water in rivers not being able to flow out at the rates it used to. Flooded fields, 50 km from Paris were rising and falling with the tides last winter...

Amos J Aug 23, 2024, 06:16 PM

Lovely! I will have a proper beachfront home and for the warmer sea, Cape Town can do with that. UnfotunatelyI will be 150 years old!

matth Aug 24, 2024, 12:46 AM

I am happy to take my chances and if this woke BS makes prices drop then WIN!

Arnold O Managra Aug 24, 2024, 05:19 AM

Remember, Don, that humans are the most adaptable species on earth. Empirically. There is no danger to the human species from human impact. Humans will adapt and survive. Life itself really doesn't care. The universe and earth have infinite time. Why so worried? Does it provide you self-virtue?

potgieterjohan123 Aug 24, 2024, 06:48 AM

It was not due to a lack of money that we bought a house, second row from the beach, oh no. We were aware that one day we will have a beachfront property. Thats clever investment.

Colin K Aug 25, 2024, 10:23 AM

Love it.

Tim Bester Aug 24, 2024, 08:07 AM

A few decades ago we, in Johannesburg, were warned that acid mine water was going to inundate the leafy suburbs of upper Houghton, Westcliff and Northcliff. Now these suburbs suffer on-going water shortages because the infrastructure is so dilapidated.

Arnold O Managra Aug 24, 2024, 10:45 AM

The worst case scenario modelled by climatologists is 20m sea rise *in the next 2000 years*. 20m is a big deal, but 2000 years ago the earth's human population was ~200 million. Too many twos. Weather catastrophe killed more people proportionally way back then. Humans are adaptive, inventive.

Joe Slabbert Aug 24, 2024, 02:15 PM

Even a centimetre or 2, spread over a vast ocean, creates massive physical dynamics. With extreme weather, it could cause devastating pounding of a coastline. Water is heavy. Much heavier than sand.

mpenzhorn Aug 25, 2024, 07:50 AM

Thank you for the article and for interesting commentary. In Australia, I have been flabbergasted to learn that the wild ocean between Airlie Beach and the great barrier reef was aboriginal land in historical memory. That really shook me out of complacency on this topic.

Colin K Aug 25, 2024, 10:24 AM

I hadn't heard of this. Thanks for the info.

Biff Trotters Aug 26, 2024, 12:29 AM

"Water is heavy. Much heavier than sand." - What? Dry sand has a density of about 1.5 x the density of water. Otherwise, well, the sand would be floating on the water. But you are correct about the pounding.

alastairmgf Aug 24, 2024, 06:39 PM

Interesting that there are two “rising sea level” articles one after another on the same day. Grist to the mill for the climate change fans.

Yoni Balkind Aug 25, 2024, 04:35 AM

How did the ocean rise by 3mm a year (ie 300mm) in the 20th century, but only rise by 20cm (ie 200mm, ie 1.5mm per year) between 1880 and 2014? Hard to rely on the data in this article when it starts off with completely contradictory figures.

chrisvan Aug 28, 2024, 07:35 AM

So then why do banks - the most conservative institutions in the world - give 30 year mortgages to sea-side developments?

Sindhu Bhogal Aug 29, 2024, 02:36 PM

because the sea-side developments, like all other developments, are insured?