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An international research team comprising scientists from the University of Hong Kong, the Nanyang Technological University, Singapore (NTU Singapore), Macquarie University and the University of Wollongong (Australia) as well as Rutgers University (USA) has predicted that mangroves will not be able to survive with rising sea-level rates reached by 2050, if emissions are not reduced. The team’s findings were recently published in one of the world’s top peer-reviewed academic journal Science.
Using sedimentary archives from the Earth’s past, researchers estimated the probability of mangrove survival under rates of sea-level rise corresponding to two climate scenarios – low and high emissions.
When rates of sea-level rise exceeded 6 mm per year, similar to estimates under high emissions scenarios for 2050, the researchers found that mangroves very likely (more than 90% probability) stopped keeping pace. In contrast, mangroves can survive sea-level rise by building vertically when the rise remains under 5 mm per year, which is projected for low emissions scenarios during the 21st century.
The threshold of 6 mm per year is one that can be ‘easily surpassed’ on tropical coastlines – if society does not make concerted efforts to cut carbon emissions, said lead investigator of the study, Professor Neil Saintilan, from the Department of Earth and Environmental Sciences at Macquarie University.
Professor Saintilan said, “We know that sea-level rise is inevitable due to climate change, but not much is known about how different rates of sea-level rise affect the growth of mangroves, which is an important ecosystem for the health of the earth.”
“Most of what we know about the response of mangroves to rising sea level comes from observations over the past several years to decades when rates of rise are slower than projected for later this century. This research offers new insights because we looked deeper into the past when rates of sea-level rise were rapid, reaching those projected under high emissions scenarios,” said Dr Nicole Khan, Assistant Professor of Department of Earth Sciences, The Unviersity of Hong Kong.
Why mangroves matter
With their iconic roots that rise from under the mud, mangrove stands grow in a process called vertical accretion. This feature is crucial to the ecosystem as it helps to soak up greenhouse gas emissions (carbon sequestration) at densities far greater than other forests, and provides a buffer between the land and sea – helping protect people from flooding on land.
The study, which covered 78 locations over the globe, explores how mangroves responded as the rate of sea-level rise slowed down from over 10 mm per year 10,000 years ago to nearly stable conditions 4,000 years later. The drawdown of carbon as mangrove forests expanded over this time period contributed to lower greenhouse gas concentrations.
The study found that mangroves will naturally encroach inland if its ability to vertically accrete is hindered.
“Our results underscore the importance of adopting coastal management and adaptation measures that allow mangroves to naturally expand into low-lying coastal areas to protect these valuable ecosystems,” said Dr Khan.
Professor Benjamin Horton, Chair of the Asian School of the Environment at NTU Singapore, who co-authored the paper, said, “In 30 years, if we continue upon a high-emissions trajectory, essentially all mangroves, including those across southeast Asia, will face a high risk of loss.”
“This research therefore highlights yet another compelling reason why countries must take urgent action to reduce carbon emissions. Mangroves are amongst the most valuable of natural ecosystems, supporting coastal fisheries and biodiversity, while protecting shorelines from wave and storm attack across the tropics,” Professor Horton added.
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Paper titled “Thresholds of mangrove survival under rapid sea-level rise”, published in Science, June 5 2020.
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“This research therefore highlights yet another compelling reason why countries must take urgent action to sustain my grants and secure my tenure.”
FIFY.
12,000 years ago sea-level was 120 metres below the present. That amounts to 10 millimetres per annum ON AVERAGE. But if the sea-level became stable at near-present levels in just 4000 years, as the authors state,the rate of change would be 25 millimetres per annum. Obviously all the mangroves died. Once more, what happened to peer review?
Last time I looked at an authority, a few minutes ago, I found this “…in subtropical and tropical regions of the world.” Mitsch and Gosselink, Wetlands, Van Nostrand Reinhold. What is the correlation of ocean productivity with the presence of mangroves, thought it was around upwelling areas in cooler climates, river deltas? A little homework would be nice. Bay de Mongles (Mangrove Bay) is 8 miles inland from the Louisiana coast, killed back by freezes, coast once had 10′ tall mangroves killed by freezes and hurricanes. When Louisiana was settled in the early18th century mangroves were so common as to hinder access.
Montz, G. N. 1977. A vegetational study of the Timbalier and Isles Dernieres barrier islands, Louisiana. Proceedings Louisiana Academy Science. 40:59-69.
Du Pratz, M. Le Page. 1774. The History of Louisiana. T. Beckett, London, 1972 Reprint, English translation. Claitors, Baton Rogue, LA.
Louisiana must be marginal for mangroves. The nothernmost I know of in Eurasia is at Sharm-el-Sheikh, Egypt about 28 deg N and the southernmost is at Wilsons Prom. Vic. 38 deg S.
What utter hogwash. Being a birdwatcher I’ve visited quite a few mangroves in my days. They are hell for mosquitos but hold a lot of interesting birds some of which are only found in mangroves.
Mangroves are quite remarkably immune to sea level changes. Some of the best and biggest mangroves I’ve seen were near Derby in West Australia. Derby is famous for its yuge tides – about 37 feet at maximum springs. The tidal range also varies from about 37 feet at springs to about half that at neap.
So those mangroves not only have to survive 30 feet sea level changes twice every 12 hours. They also must survive that the maximum and minimum sea levels change up and down about 10 feet every two weeks:
https://www.tide-forecast.com/locations/Derby-Australia/tides/latest
And of course there is also longer term variations, tides vary over longer periods too, due to the varying interactions of solar and lunar tides and the Earth’s elliptic orbit, annually and over longer periods (up to 18,000 years). Not very much of course but a lot more than 6 mm over a year. I couldn’t find a longer-term curve for Derby, but here is one for Seattle:
None of this seems to inconvenience the mangroves.
Also mangroves have a remarkable system for seeding. The seeds sprout while still on the mother tree, and are dropped as seedlings with both roots and leaves (vivipary), these seedlings drift vertical in the water with roots down until they “touch bottom” and settle. If sea-level goes up 6 mm per year I expect that the seedling may have to drift a foot or even two further before taking root. I think this is survivable.
And after all mangroves survived MWP-1A (Meltwater Pulse 1A) about 14,000 years ago when sea-level rose about 20 meters in 500 years.
And they not only survived. Remember the birds I mentioned earier, that only live in mangroves. They didn’t evolve in the last 14,000 years, so apparently mangroves managed managed to stay intact enough, and large enough for the birds and other mangrove endemics (there are quite a few) to survive too.
“When rates of sea-level rise exceeded 6 mm per year, similar to estimates under high emissions scenarios for 2050, the researchers found that mangroves very likely (more than 90% probability) stopped keeping pace”
At the end of the last glacial period, sea level rose by 120 metres in approximately 7,000 years. According to my pocket calculator, that’s an average of 17 mm/year. And during meltwater pulse 1A, it rose by ±30 metres in ±1,000 years or ± 30 mm/year. Possibly as much as 12 metres in 130 years (but the data are a bit too sparse to be certain of this) which equates to 92 mm/year.
One of the great unanswered questions of the last 100 years was “Where have all the mangroves gone?” At last, we have an answer!
Joking aside, this study not only ignores knowledge that can be acquired in less than a minute on the internet, but it’s also common knowledge among anyone who has the slightest knowledge of earth history. Five (or possibly six) of the eight authors are in Earth Science departments of their respective universities in Australia, Hong Kong, USA and Singapore. Wouldn’t that mean that they’ve taken a couple of geology courses? Read a geology textbook? Talked to a colleague who has taken courses and read a geology textbook? Apparently not, because they don’t know what happened in the Holocene! Or is it possible that they do know, don’t care, and published this monstrosity anyway?
We’ve become so used to junk science in the climate field that we’re almost anaesthetized to it, but this is exceptional. If I hadn’t seen it in print*, I wouldn’t have believed that such lack of knowledge was even possible in what we used to call institutions of higher learning. I nominate this paper for the Golden Trashcan Award. It achieves a truly superhuman level of ignorance and deserves to be memorialized as such. If we don’t preserve this work for posterity, future generations will never believe that we could collectively have been so dumb.
* the paper is paywalled so I just read the abstract.
Low emissions = good.
High emissions = bad.
How amazingly convenient!
I am not going to bother to look this up, but I think the rate of rise of the mean sea level during the early Holocene, when the glaciers covering the northern hemisphere melted was much more than 6 mm/yr. and yet the mangroves still exist.
“…University of Wollongong (Australia)…”
With this addition their credibility has just been lost.
A race to the bottom with JCU !
What is an “international scientist”?