Guest essay by Eric Worrall
A JPL led study has suggested construction of water reservoirs in the 1970s held back so much water from running into the sea it paused sea level rise.
Climate change: Dams played key role in limiting sea level rise
By Matt McGrathEnvironment correspondent
The construction of large-scale dams has played a surprising role in limiting rising seas, say scientists.
Over the past century, melting glaciers and the thermal expansion of sea water have driven up ocean levels.
But this new study finds that dams almost stalled the rising seas in the 1970s because of the amount of water they prevented from entering the oceans.
Without them, the annual rate of rise would have been around 12% higher.
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Read more: https://www.bbc.com/news/science-environment-53836018
The abstract of the study;
The causes of sea-level rise since 1900
Thomas Frederikse, Felix Landerer, Lambert Caron, Surendra Adhikari, David Parkes, Vincent W. Humphrey, Sönke Dangendorf, Peter Hogarth, Laure Zanna, Lijing Cheng & Yun-Hao Wu
The rate of global-mean sea-level rise since 1900 has varied over time, but the contributing factors are still poorly understood1. Previous assessments found that the summed contributions of ice-mass loss, terrestrial water storage and thermal expansion of the ocean could not be reconciled with observed changes in global-mean sea level, implying that changes in sea level or some contributions to those changes were poorly constrained2,3. Recent improvements to observational data, our understanding of the main contributing processes to sea-level change and methods for estimating the individual contributions, mean another attempt at reconciliation is warranted. Here we present a probabilistic framework to reconstruct sea level since 1900 using independent observations and their inherent uncertainties. The sum of the contributions to sea-level change from thermal expansion of the ocean, ice-mass loss and changes in terrestrial water storage is consistent with the trends and multidecadal variability in observed sea level on both global and basin scales, which we reconstruct from tide-gauge records. Ice-mass loss—predominantly from glaciers—has caused twice as much sea-level rise since 1900 as has thermal expansion. Mass loss from glaciers and the Greenland Ice Sheet explains the high rates of global sea-level rise during the 1940s, while a sharp increase in water impoundment by artificial reservoirs is the main cause of the lower-than-average rates during the 1970s. The acceleration in sea-level rise since the 1970s is caused by the combination of thermal expansion of the ocean and increased ice-mass loss from Greenland. Our results reconcile the magnitude of observed global-mean sea-level rise since 1900 with estimates based on the underlying processes, implying that no additional processes are required to explain the observed changes in sea level since 1900.
Read more: https://www.nature.com/articles/s41586-020-2591-3
A few mm / year of sea level rise is no threat to anybody’s wellbeing. But I find it fascinating that constructing a few dam projects was apparently enough to stall this allegedly serious climate threat.
If building a few dams in the 1970s was enough to stall sea level rise, there are plenty of other gigantic water projects on the drawing board which would likely stall sea level rise for a few more decades, such as the Egyptian Qattara Depression Project, the CSIRO Three Rivers Northern Catchment Scheme, or one of the many variations of the Bradfield Scheme. China has a large area of useless wasteland which could conceivably be filled with water. Even filling these natural depressions with sea water in many cases could improve the local microclimate.
“But this new study finds that dams almost stalled the rising seas in the 1970s because of the amount of water they prevented from entering the oceans.
Without them, the annual rate of rise would have been around 12% higher.”
12% is “almost stalled”?
What a bunch of malarkey.
12% is 12%.
Less than one eighth.
How does reducing the rate of rise by one eighth mean it was “almost stalled”?
I don’t think they ever actually saw an ocean. They need to take a ride on a freighter across the Pacific to get some respect for the size of the thing.
It cost a lot of money to build a dam. They aren’t built without a reason.
They are built so the water is available to use and/or prevent flooding. (By “to use” I’m including hydro and recreational use.)
The water used from what is pooled behind it does not disappear.
It is mostly returned to the rivers via wastewater plants, transpiration if used for irrigation, etc.
Again, the water doesn’t disappear. It will still end up in the oceans where some will evaporate and again fall as rain or snow.
What impact do shingled roofs, sidewalks and paved roads have on sea level? Millions of acres of material designed to shed water which often are complimented by sewers and storm drains, that empty into the oceans.
How much water by dint of human activity is ushered via the most direct path to the oceans where it would have otherwise been absorbed by the soil and sequestered in a pond, lake or aquifer?
Since when is a 12% reduction a “pause”? Reducing 3mm of sea level rise by 12% would still mean 2.97 mm of sea level rise. Who publishes this crap?
Pachygrapsus
It is published by those shackled to the “Publish or Perish” job requirement. It is the quantity of publications, not the quality, that governs raises.
Let’s just do a little calculation. Take the area of the world’s oceans. Assume a 1″ (OK, 3 cm) depth, and work out the volume of that sheet. (Scientific notation is encouraged.) now compare that to the volume of water behind dams. I haven’t done that yet, but I’m betting there’s a big difference.
Why should there be any sea level rise since the meteor that caused the extinction of the dinosaurs? The amount of water on this planet has remained constant since the seas were formed 3 1/2 billion years ago. Have you all overlooked the fact that these dams you are talking about are on land, all of which are on tectonic plates, which in turn, float of the earth’s mantle which in turn is made up of molten rock.
Archimedes principle applies here. When an object is wholly or partially immersed in water the weight of water displaced equals the weight of the object. If this were not true ships would not float to their designed water mark. The principle would still apply to any liquids.
Try a little experiment. Fill a jug with ice then top it up to the brim with water. You should notice that about 1/5th of the ice will protrude above the rim of the jug. Now let the ice melt and see how much water spills over the side of the jug. This test should show you that the claim by climate changers of catastrophic sea level changed by melting of ice is totally false.
If the sea raises in one place it must rise by the same amount in another place. Water is incompressible. We do of course have tides, storm surges and the effects of the spinning earth which causes water depths to increase on the eastern side of continents and not so on the western side. Also aren’t most of these claims of sea level changes, if not all, the result of tectonic movements or gravitational pull or the earth’s momentum? Certainly not by atmospheric activities – heat rises, carbon absorbs heat, not generate it.
When Captain John Hunter of HMS Serius came to Australia in 1788 with the First Fleet, he carried out a complete survey of Sydney and environs. He determined the sea level of the maximum spring tide and put a mark on a rock at Fort Denison which became the base datum line (BDM) for measuring all heights in the Sydney region. As far as I can ascertain there has been no adjustment to this line.
The Amazon river has a fifth of the worlds fresh water flowing out of it and the mouth is a hundred miles wide. Tell me again how many dams are on it?
I can’t believe how stupid some in the world are and what they will believe. Anything to try and push the agenda. I can understand the Three Gorges dam having some affect and even the Hoover Dam but the rest would be like a flee on a dog. It might be interesting to see if any dams break in China with their latest edict.
Just as well we have a sense of humor. The bully’s of this world love to spook everyone with the boogeyman, this one being climate change, nee global warming, nee global cooling. When the Snowy River scheme, a huge irrigation project on the border of New South Wales and Victoria, states of Australia, was built there was no discernable change in the tides around the coast of Australia. Within the same time we built Hume Reservoir, Burrenjuck Dam, Warragamba Dam, and the great Lake Argyle in Northern Territory and we still got no tidal increase and there have been a lot of similar dams building going on around the world in other countries.
My uncle made the pumps for the Snowy River scheme and my father who was about 5ft 10in could walk through them without ducking. They must have pushed a hell lot of water through.