Asian sea levels changed rapidly 6,000 years ago — natural sea level rise “unprecedented”

If you thought seas were constant 6,000 years ago…

Microatolls are apparently very accurate proxy for sea levels, giving a higher resolution estimate of sea levels. But the extra data suggests more natural oscillations in seas than the experts used to think. Six thousand years ago, near Indonesia, seas apparently rose and fell twice by as much as 60 centimeters in a 250 year period. A similar pattern happened 2,600km away in SE China. Seas were changing so fast researchers estimate the shift occurred at 13mm per year and comment that these regional changes are “unprecedented in modern times.” (Or unrepeated, perhaps?) At the first peak 6,750 years ago, seas were 1m higher than today. The current rate of sea level change is 1mm a year in hundreds of tide gauges and 3mm in “adjusted” satellite data).

From the paper I gather that sea levels in this region change a lot even now. ENSO and the Indian Ocean dipole slop the oceans back and forward. Meltzner et al don’t know why the seas around asia changed so much in the holocene, nor do they know if this is a global phenomenon. They talk about other studies on the Great Barrier Reef and …suggest that oscillations may be more common than previously appreciated,.. (but they don’t have the resolution yet to know. )

You and I might think this shows that the climate changes all by itself (and CO2 was irrelevant). You might also think that it shows climate models are incomplete because they have no idea what caused this. But sieve your brain through the Global Worrier Cult and you will come to realize that a sea level event that we don’t understand, and can’t predict, means we should worry even more about CO2. Because why? Because, who knows, bad stuff might happen again. This is what Meltzner et al conclude. Perhaps it’s a “safe caveat” so Nature will still publish their inconvenient results, but they do go on in the paper a bit.

If they’d found no swings, presumably the press release would tell us how the modern 1mm a year rises are unprecedented. There is a relentless progression of papers showing past climate was wilder than we thought, and natural climate change is more important. Whatever they find, the press release message ends up being “panic more”. Trite.

– Jo

PS: For perspective, sea levels around Australia in the Holocene peak 7,000 ya were 1 – 2m higher and have been falling since then. (But notice the resolution on those Australian graphs at that link are nowhere near as good as this new study). Further back in the past, sea levels were 9m higher around Kalbarri Western Australia circa 120,000 ya.

[ScienceDaily] For the 100 million people who live within 3 feet of sea level in East and Southeast Asia, the news that sea level in their region fluctuated wildly more than 6,000 years ago is important, according to research published by a team of ocean scientists and statisticians, including Rutgers professors Benjamin Horton and Robert Kopp and Rutgers Ph.D. student Erica Ashe. That’s because those fluctuations occurred without the assistance of human-influenced climate change.

In a paper published in Nature Communications, Horton, Kopp, Ashe, lead author Aron Meltzner and others report that the relative sea level around Belitung Island in Indonesia rose twice just under 2 feet in the period from 6,850 years ago to 6,500 years ago. That this oscillation took place without any human-assisted climate change suggests to Kopp, Horton and their co-authors that such a change in sea level could happen again now, on top of the rise in sea level that is already projected to result from climate change. This could be catastrophic for people living so close to the sea. “This research is a very important piece of work that illustrates the potential rates of sea-level rise that can happen from natural variability alone,” says Horton, professor of marine and coastal sciences in the School of Environmental and Biological Sciences. “If a similar oscillation were to occur in East and Southeast Asia in the next two centuries, it could impact tens of millions of people and associated ecosystems.”

What this study shows is that we need to figure out what really drives climate change (like something on the Sun, perhaps?)

Meltzner, a senior research fellow at Earth Observatory of Singapore at Nanyang Technological University, along with Horton, Kopp and their co-authors, used coral microatolls to understand when, and by how much, the sea level had risen and fallen near the Indonesian island of Belitung, which lies between Sumatra and Borneo. A microatoll is a circular coral colony, typically no more than about 20 feet across, in which the topmost coral is dead and the bottom part living and growing. By taking samples from microatolls in different places, scientists can date rises and falls of sea level.

The microatolls are what scientists call a “proxy” — a natural process that provides a reliable record of past events. “In any region, you try to find the proxy controlled by sea level,” Horton says. “In New Jersey, we have no corals, so we use salt marshes. In the tropics, corals are the go-to proxy.”

The scientists studied microatolls at two sites on opposite sides of the island. Meltzner says they didn’t expect the fluctuations they found because those changes in sea level contradicted what they knew about sea level in Southeast Asia. “Our conventional understanding of ocean circulation and ice-melting history told us that such fluctuations should not occur, so we were a bit mystified at the results from our first site,” Meltzner says. “But after finding a similar pattern at a second site 80 kilometers to the southeast, and ruling out other plausible explanations, it was clear that the coral growth patterns must reflect regional changes in sea level. There would be way too many coincidences otherwise.”

The paper comes out of a long-running research project aimed at understanding the physical processes involved in sea-level rise. Such understanding, Kopp says, is necessary to help scientists understand the present and likely future state of the ocean. “This is a basic science problem,” Kopp says. “It’s about understanding past changes. Understanding what drove those changes is what allows us to test the climate models we use to predict future changes.”

Press Release provided by Rutgers University. Original written by Ken Branson.

l Reference:

Aron J. Meltzner, Adam D. Switzer, Benjamin P. Horton, Erica Ashe, Qiang Qiu, David F. Hill, Sarah L. Bradley, Robert E. Kopp, Emma M. Hill, Jędrzej M. Majewski, Danny H. Natawidjaja, Bambang W. Suwargadi. Half-metre sea-level fluctuations on centennial timescales from mid-Holocene corals of Southeast Asia. Nature Communications, 2017; 8: 14387 DOI: 10.1038/ncomms14387

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