Alert readers of the Guardian website may remember a rather sensational article posted there as long ago as 11th July 2016, under the heading “Massive mangrove die-off on Gulf of Carpentaria worst in the world, says expert”. It was said that an El Niño event played a part, but climate change also got the blame:
Climate change and El Niño have caused the worst mangrove die-off in recorded history, stretching along 700km of Australia’s Gulf of Carpentaria, an expert says.
Needless to say, the opportunity was also taken to say that all this destruction, the result of climate change, coincided, with “the world’s worst global coral bleaching event, as well as the worst bleaching event on the Great Barrier Reef”, which was also attributed to “unusually warm water”.
Without any sense of irony:
Norm Duke, an expert in mangrove ecology from James Cook University, flew in a helicopter over 700km of coastline, where there had been reports of widespread mangrove die-offs.
He was “shocked” by what he saw. He calculated dead mangroves now covered a combined area of 7,000 hectares…
The clear culprit in this case was climate change, which was warming waters and making rainfall more erratic, Duke said. That put the mangrove forests at their tolerance limit, and when a strong El Niño hit the world this year – warming waters in northern Australia and drawing rainfall away – they were pushed past their tolerance thresholds.
In the wake of the scare stories about the Great Barrier Reef turning out to be overdone, there is now a similar development regarding the mangrove swamps. Not, sadly, in this case, that they have recovered in a way that surprises experts and confounds the climate change hysteria. Rather, that experts have now decided that the “clear culprit” in this case is not, after all, climate change. Today the Guardian has an article with a rather different heading: “‘Wobbly’ moon probable cause of mass tree deaths in Australia, scientists say”.
Well then, what’s the story now?
A wobble in the moon’s orbit around Earth affects mangrove cover across Australia and likely contributed to mass tree deaths in the Gulf of Carpentaria, new research suggests.
A study published in the journal Science Advances has found that an 18.61-year cycle known as the lunar nodal cycle shapes the condition of tidal wetlands…
…Along the Arnhem coast in the Northern Territory and the Carnarvon coast in Western Australia, the researchers found that peaks in closed canopy cover – where thickened mangrove canopy covered more than 80% of ground area – coincided with the peak tidal phases of the moon’s wobble.
They believe the lunar wobble likely contributed to mass mangrove dieback in the Gulf of Carpentaria in 2015-16, an event in which an estimated 40m trees died. At the time, a “low tidal range” phase of the lunar wobble coincided with a severe El Niño.
“They had a combination of a 40cm drop in the mean sea level associated with the El Niño and, on top of that, a 40cm drop in tide range [due to the lunar wobble],” Saintilan said. “There were mangroves in creeks [previously] being inundated every day that might have been inundated just a handful of times in the whole of the dry season.”
A quirk of the lunar wobble is that it has the opposite tidal effects along coastlines which have one high tide daily compared to those that have two high tides daily.
In a region with only one daily high tide, a phase of the lunar cycle may result in a lower tidal range and less frequent water inundations. The same phase will have the inverse effect along coastlines with two daily high tides, resulting in more mangrove inundation.
The Gulf of Carpentaria is one of few Australian coastlines that has one high tide daily. Mangroves in adjacent regions that survived the 2015-16 El Niño were in a “high tidal range” phase of the lunar cycle. The El Niño was previously thought to be the cause of the mass dieback [and climate change – don’t forget climate change!], but “the nodal cycle also seems like a necessary condition for mangrove mortality”, Saintilan said…
What? Not climate change? Er, no…:
“So far, global warming has been good for mangroves. With higher sea levels they’ve been expanding into areas that they could not survive before,” he said.
Far from being the “clear culprit”, we are now told that climate change (or its nominal predecessor, global warming) has been good for mangroves. Whatever next?
Mark, thanks for highlighting this. It’s a reminder for me that ecology is perhaps not what it used to be: once a science, now it is a feeling.
The key thing that ecologists once knew about intertidal habitats is that they occupy a strip that is “just right” for them. The plants on the seaward edge of the land are typically stress-resistant specialists, which cannot survive in competition with entirely terrestrial plants. Higher plants have roots, and require soft sediment. (Intertidal algae, which do not have roots, are able to colonise rocks.) Plants may increase sedimentation, which raises (and drains) the land. This eventually becomes suitable for terrestrial plants, which can out-compete the specialists.
If you knock out a band of mangroves, the habitat will be recolonised. This is a normal and natural phenomenon – or it was, until ecology stopped being science and became a feeling.
How is climate change supposed to affect mangroves, which thrive in the hottest climates where suitable sediment is available? The only rational possibility is by rising sea level, if that could exceed the deposition rate of the trapped sediment. But this misunderstands coastal dynamics, which are hardly ever due to sea levels rising or falling, but due to sediment being picked up in one place and dropped in another. That is, the band of habitat may move, but it won’t shrink.
Now let’s talk about the actual threats to mangroves, and the connection with climate change. Here’s a Google Earth snip of mangroves at Cap-Haitien, 2004:
Now let’s see how it looks today:
This is what the houses look like:
Photo by Rémi Kaupp from: wiki at https://en.wikipedia.org/wiki/Mangrove_tree_distribution
What happens when a storm washes all this away?
It will be blamed on climate change.
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The above comment was slightly edited because I mangled the tag (which I later removed so the photo could be seen as embedded.) The original caption at wiki says
Thanks for that – very interesting indeed.
I have given the Guardian credit for running the story suggesting that climate change isn’t the culprit. However, I give them no points in respect of their failure to refer back to their earlier article and issue a correction, and their failure to alert their readers to the fact that increasingly alarmist claims about climate change are being debunked. To read the latest article, you would think nobody ever said “The clear culprit in this case was climate change, which was warming waters and making rainfall more erratic…”.