From the UNIVERSITY OF HAWAII AT MANOA
Historical records may underestimate global sea level rise
New research published in Geophysical Research Letters shows that the longest and highest-quality records of historical ocean water levels may underestimate the amount of global average sea level rise that occurred during the 20th century. Dr. Philip Thompson, associate director of the University of Hawai’i Sea Level Center in the School of Ocean and Earth Science and Technology (SOEST), led the study.
“It’s not that there’s something wrong with the instruments or the data,” said Thompson, “but for a variety of reasons, sea level does not change at the same pace everywhere at the same time. As it turns out, our best historical sea level records tend to be located where past sea level rise was most likely less than the true global average.”
A team of earth scientists from the University of Hawai’i at Mānoa, Old Dominion University, and the NASA Jet Propulsion Laboratory worked together to evaluate how various processes that cause sea level to change differently in different places may have affected past measurements. One particularly important concept is the existence of “ice melt fingerprints”, which are global patterns of sea level change caused by deviations in Earth’s rotation and local gravity that occur when a large ice mass melts. Each glacier, ice cap, or ice sheet has a unique melt fingerprint that can be determined using NASA’s GRACE satellite measurements of Earth’s changing gravitational field.
During the 20th century, the dominant sources of global ice melt were in the Northern Hemisphere. The results of this study showed that many of the highest-quality historical water level records are taken from places where the melt fingerprints of Northern Hemisphere sources result in reduced local sea level change compared to the global average. Furthermore, the scientists found that factors capable of enhancing sea level rise at these locations, such as wind or Southern Hemisphere melt, were not likely to have counteracted the impact of fingerprints from Northern Hemisphere ice melt.
“This is really important, because it is possible that certain melt fingerprints or the influence of wind on ocean circulation might cause us to overestimate past sea level rise,” said Thompson, “but these results suggest that is not likely and allow us to establish the minimum amount of global sea level rose that could have occurred during the last century.”
The investigation concludes that it is highly unlikely that global average sea level rose less than 14 centimeters during the 20th century, while the most likely amount was closer to 17 centimeters.
The full paper can be found here, and more information about sea level change can be found on the University of Hawai’i Sea Level Center website and the NASA sea level change website.
###
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
How do they know it’s underestimated if they don’t have measurements for higher than average places?? Doesn’t make any sense, and so can only be unsubstantiated conjecture.
Who knows the exact average incidence of the seafloor up or dowliftings (sometimes on very large areas) due to huge tectonic forces on the sea level rise ?
Isn’it a too easy answer to say that the balance between ups and downs is probably ~ 0
I’m only interested in the change in high tide level. No change there, who cares?
“The investigation concludes that it is highly unlikely that global average sea level rose less than 14 centimeters during the 20th century, while the most likely amount was closer to 17 centimeters.”
I thought the rough guide we’d been using for some time was 2-3 millimetres per year, which would be 20-30 centimetres per year, so the conclusion of the paper is that global sea level rise is LESS than I thought.
The thing that bugs me is that they are basically saying that the historic record is incapable of detecting something that MIGHT have happened therefore it DID happen. Have I got that right? Isn’t this a case of absence of evidence being taken as evidence of presence?
If they are right, and the sea level is higher in places we aren’t interested in, does it matter to human society?
As it turns out, our best historical sea level records tend to be located where past sea level rise was most likely less than the true global average.”
translates to
“We neither have data nor clue of what we are talking about. We’re standing here empty handed.”
This paper is really just an academic tempest in a teapot. Statements like this: “…the longest and highest-quality records of historical ocean water levels may underestimate the amount of global average sea level rise that occurred during the 20th century” presuppose that the most important metric is “global average sea level”, which I take it is some average height of the ocean surface relative to the center of the (non-spherical) earth, as if that can actually be measured to sub-millimeter accuracy.
But isn’t the only measure of sea level of real engineering or human significance the local measurement of sea level relative to land that people occupy? And isn’t that exactly what’s been measured by tide gauges for centuries–said measurements showing a constant rate of sea level rise?
Academics can speculate and pontificate ad nauseum about complex motions of land, ice, and water which lack empirical support but somehow “might” or “could” magically deliver the observed zero acceleration of tide gauge readings, but so what? Occam’s Razor still applies. If tide gauges show no acceleration in sea level rise, there is no observable impact of CO2 on this most important metric, and no rational basis for a belief that expensive reductions in CO2 emissions would reduce nonexistent acceleration in sea level rise near land that humans occupy.
I imagine they would love to add Kansai Airport to the dataset.
https://www.linkedin.com/pulse/enginering-went-totally-wrong-kansai-airport-japan-ocean-nawaqavou