Study found evidence for a period of enhanced pre-industrial sea-level rise of about 2-3 millimeters per year
University of York
The study, led by the University of York, found evidence for a period of enhanced pre-industrial sea-level rise of about two to three millimetres per year in three locations: Nova Scotia, Maine and Connecticut.
The researchers say that the large rises at these three locations were natural, and partly related to the North Atlantic Oscillation – a large-scale atmospheric pressure see-saw over the North Atlantic region – and to periods of enhanced ice melt in the Arctic.
The authors of the study say cities like New York and Boston will have to take into account this natural variability in planning for future sea level rise.
The findings are based on sea level reconstructions derived from salt-marsh sediments from the Atlantic coast and from microscopic salt-marsh fossils.
Previous studies have shown that, since the 1950s, rates of sea level rise along the Atlantic coast of North America were faster than the global average – leading to this region coming to be known as a sea level rise “hotspot.”
However, lead author Prof Roland Gehrels, from the University of York’s Department of Environment and Geography, said this earlier rapid episode of sea level rise in the 18th Century wasn’t known before.
“To find out what global warming is doing to sea levels today we need that base level from historical times.
“In the 20th Century we see rates of up to three or four millimetres per year, faster than in any century in at least the last 3000 years.
“In the 18th Century they were slightly slower, but still much quicker than you would expect for the Little Ice Age, partly because the Arctic was relatively warm during the 18th Century.
“It is pre-industrial so there are no anthropogenic forces – or human influences – at play, but in the 20th Century there may well have been.
“This means that those rapid episodes of sea level rise on the north east coast of North America in the 18th Century have a natural cause.”
Scientists say salt-marshes are good “archives” of sea levels as they contain several metres of sediment which contains data going back hundreds of years.
Prof Gehrels added: “The high rates in this “hotspot” could present significant coastal risks for large population centres if they are a persistent and recurring feature.
“The likely future sea level rise in places like New York City is expected to be considerably greater than the global average by the end of the 21st century.”
“Our findings suggest that enhanced rates of sea level rise along eastern North America are not only symptomatic of human activity, but might additionally arise from natural processes in the climate system.”
The findings are published in Geophysical Research Letters and involved collaboration with the University of Leeds; Durham University; Bangor University; the National Oceanography Centre, Liverpool; Woods Hole Oceanographic Institution, Massachusetts, USA; Old Dominion University, Virginia, USA; and the University of Siegen, Germany.
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As the actual Arctic is a floating piece of ice rather than land, as I understand it, any change to the Arctic’s ice mass would not in any way, affect the sea-level, according to Archimedes of Syracuse (Archimedes’ Principle).
Based on the researchers’ claim, it seems that we would have to assume that the authors were referring to something more than the actual Arctic, like maybe all land and ice within the Arctic Circle as being the Arctic(?).
The NOAA website makes no sense. It says:
Sea level rise at specific locations may be more or less than the global average due to many local factors: subsidence, upstream flood control, erosion, regional ocean currents, variations in land height, and whether the land is still rebounding from the compressive weight of Ice Age glaciers.
How does local subsidence cause ocean levels to rise? They can’t, unless it’s on a massive scale, either tectonic or orogenic. Instead of heeding their own words of caution, the measurements are incorrectly reported by NOAA, hoping no-one will notice. They never state that the datum has moved. Instead of reporting that the apparent change in sea levels is due to subsidence, they imply that the land datum is fixed and the relative movements are all due to sea level rise. NOAA won’t admit that islands on coral atolls in the South Pacific are sinking into the South Pacific, not the other way round. They are sinking is exactly as Darwin said they would. However, the myth must be maintained by NOAA at all costs.
What has upstream flood control got to do with sea levels? If the gauges are in river mouths, they should not be using this data for global studies. That should only be used for shipping.
How does one make sense of the statement that “variation in land height affect tide levels”? In the words of Fermi, it’s not even wrong.
If “the land is still rebounding from the compressive weight of Ice Age glaciers”, then it should be reported as such, not as a change in sea levels. But they don’t.
NOAA forgot to mention Gilligan moving the Professor’s measuring stick.
“The researchers say that the large rises at these three locations were natural, and partly related to the North Atlantic Oscillation – a large-scale atmospheric pressure see-saw over the North Atlantic region – and to periods of enhanced ice melt in the Arctic.”
That has to be negative NAO, but they don’t say which decades of the 18th century.
PGR — Post Glacial Rebound
There were studies on this I haven’t found time to retrace yet. The coastal area from just north of New York City is descending 1-4mm /year if my memory is right. This has been known since the 1950’s. The largest change downward is at the northern end at New Brunswick- Prince Edward Island. The coastal area was pushed up as the inland areas were depressed from the weight of the 1-2 miles of glacial ice that covered the interior.
The simple way to visualize this process (for teachers of geology) is to make a circle with your thumb and index finger. put a small piece of paper over the “hole”, and lightly press down the paper over the middle of the hole. paper outside the hole tilts up as the center depresses. Release the pressure on the center, and as it rises the outside of the paper falls again.
It only looks like sea level rise, if you don’t take into account the possibility that the land may be depressing.
I am confused? Why is this article characterizing a period of 2 to 3 mm annual sea level rise as exceptional?
Isn’t that precisely the long-term average of sea level rise?