The Moon;
Earth’s natural satellite, orbiting approximately 384,400 km away. A celestial object that
scientists have studied for thousands of years, using its regular motions to mark the passage
of time in calendars. Its dependable rhythms helped ancient civilisations to track when
to plant crops, and its waxing and waning faces cemented the Moon’s place deep in the
heart of symbol and tradition. It’s a wonder, a necessity… and a curse. While the Moon’s desolate
beauty has captured the vision of poets, it also brings desolation. There is one lunar
rhythm that is not helpful to us; a 19-year cycle that brings unexpected floods and ruin.
And NASA scientists are worried that in the middle of the 2030’s,
it’s about to hit its hardest yet. For ecosystems that are adapted to
it in the right way, this won’t be a problem. But … How adapted are we?
I’m Alex McColgan, and you’re watching Astrum. Join with me today as we learn about the
innocently named Lunar Nodal Cycle and why we need to start developing a much better understanding
of the fluctuating behaviour of our Moon if we are to protect ourselves against its dangers.
Much like the Sun, the Moon is an inescapable part of life on Earth, the Moon has an immense
impact on our planet. You likely have already heard how its cycles influence our wildlife,
affect our climate, and create tides. We tend to imagine that the Moon and the Earth’s
gravities cause them to circle each other in a relatively stable, synchronised harmony;
but as is so often the case, nature is not as simple as we imagine it. Instead, every 18.6 years
the Moon’s orbit undergoes a subtle revolution. A shift in its alignment between us and our Sun that
causes high tides to grow even higher, tipping us over the edge into dangerous flood territory.
But let’s delve deeper into what this “subtle revolution” is. Its name is the ‘Lunar Nodal
Cycle’ , or the ‘precession of lunar nodes.’ This complex name refers to a specific feature of the
Moon’s orbit of the Earth. You likely know that every 29.5 days the Moon orbits the Earth.
However, this orbit is not flat. Or, to be more specific, there is a 5 degree difference
between the angle of the Moon’s orbit, and the ecliptic plane – the 2D plane on which
the Earth orbits around the Sun. For half of the month, the Moon is slightly higher than the plane
of the ecliptic. For the other half, it drops below it. Naturally, this means that there are
two crossover points – or two nodes, an ascending node and a descending node – that mark the point
whereby the moon goes from one side over to the other. And it is these nodes that move over the
course of the 18.6 year cycle, slowly rotating around the planet in one complete revolution.
The nodes themselves are what causes the problem. To understand why, let’s recap what we know about
tides. You may already be familiar with how the Moon’s gravity pulls the Earth’s water towards it,
causing a bulge in sea levels on the side closest to it that we call high tide. You
likely also know that this happens on the side of the planet furthest away from the
Moon. Rather than being caused by gravity, this second bulge is caused by centrifugal forces,
as the Earth and the Moon’s gravitational pull on each other causes them to behave
like two dancers holding each other by the arms and spinning across the dance floor. While it’s
mostly the Moon moving, due to the Earth being much more massive, the Earth is also
swung around a little. The water behind it is thus trying to fling off into space through its
raucous spinning, causing the second high tide. The Sun also has a role to play in tide formation,
albeit to a lesser degree. It’s a bigger mass which would cause a greater pull if it were
closer, but its further distance means that the Sun’s effect is only one/third as big as the Moon.
When the Moon and Sun are aligned, we get extra-large tides called Spring tides;
this happens 6 to 8 times a year. When not aligned, they partially
cancel each other out, causing smaller tidal extremes known as Neap tides.
So now consider the influence of lunar nodes on this tidal tug of war. During spring tides,
the pull of the Sun and the Moon working in unison causes the highest tides, and the largest risk of
floods. However, the Sun and Moon are never more aligned than they are at a node. During the rest
of each 9.3 year phase they are not quite tugging in the same direction, so tides are
more temperate. At a node? That’s where things get more serious, and risk of floods become highest.
The last time this alignment occurred in September 2015, the UK and US both issued major flood
warnings to their citizens. In September itself there were floods, albeit minor ones, but it was
only when heavy rain combined with the strength of the lunar nodes a couple of months later that the
real damage was inflicted. In the US in October, South Carolina saw flash flooding that caused
property damage and people having to be rescued by emergency services. At the end of December 2015,
the UK was hit by some of the worst floods it had seen in a century. Combined with the power
of Storm Desmond, flooding and storm damage caused an estimated £1.3 billion in damages.
These floods can be highly damaging… but that in and of itself doesn’t completely
explain NASA’s worry for the upcoming alignment in mid-2030. There is an extra element at play,
beyond the regular rhythm of this rising flood risk we have been
seeing throughout the course of human history. Unfortunately, the next node’s alignment with
the Sun promises to be particularly devastating. The danger is that this phenomenon is combined
with an already strained system - even more strained than it was in 2015. Climate change
has resulted in steadily rising sea levels. When the next node aligns with the Sun in
the mid-2030’s, this will likely lead to a dramatic increase of floods on planet Earth.
Worryingly, a new study led by the NASA Sea Level Change Science Team predicts that almost all US
mainland coastlines, Hawaii and Guam will have a huge leap in flood numbers when this happens. Some
predictions claim this node alignment could cause four times the amount of flooding from one decade
to the next, which will damage infrastructure and change our coastlines around the world. This means
human life will inevitably be affected by these floods, impacting shelter, clean water supplies,
electricity, as well as the increased risk of waterborne disease outbreaks, like hepatitis A and
cholera. Plus the receding flood water can create stagnant pools of water where mosquitoes gather,
which can spread other diseases like malaria.This has a knock-on effect on economic issues, as these
natural events can make coastal life unaffordable with increased cost of insurance on these homes,
or an inability to find insurance at all, which could cause a reduction in asset value
in the community. Consequently, this lunar nodal cycle will damage the quality of life in coastal
communities, where infrastructure may not be rebuilt or adapted to this force of nature.
It's not just bad for humans. Ilia Rochlin, a visiting professor at Rutgers University
analysed that the peak of the lunar wobble where high tides are higher can drown salt marshes.
Salt marshes are a habitat for a range of species, such as invertebrates, and these floods can cause
these creatures to drown, which means that other species, like fish, seabirds, and others who rely
on invertebrates to survive also suffer. And they aren't the only ones that rely on salt marshes, as
salt marshes hold a multitude of marine life which includes 75% of all fishery species. This means
that the lunar wobble impacts the food chains of humans and animals,, causing disturbances to their
natural habitat and impacting their populations. While this all does seem fairly doom and gloom,
it’s interesting to note that not all ecosystems on the planet are negatively affected by flooding
and high tides. Ecologist Neil Saintilan of Macquarie University analysed that the lunar
nodal cycle impacts heavily on the expansion and contraction of mangrove canopy cover over most of
the Australian continent. The analysis showed that the peaks of the lunar nodal cycle coincided with
the cover of the mangrove canopy. It showed that when the lunar wobble is at its minimum phase,
it causes the mangrove ecosystems to become very dry, which leads to thinner canopy cover. Yet,
when the lunar wobble is at its maximum phase, mangrove growth increases.
Mangrove canopies are beneficial to Earth’s environment as they are complex ecosystems
that fight against climate change, protect wildlife and shield coastlines. They can
also absorb four times as much carbon dioxide than rainforests of the same
size. Their growth is vital to the welfare of our planet. So, it’s not all down-side.
Still, it’s clear that if we don’t plan ahead, coastal cities and environments
will face a serious crisis. The all-important question, then, is ‘what can we do about it?’
One method is better protection. As mentioned previously, the protection and restoration of
mangroves can act as a shield against flooding, as they can mitigate the vulnerability of communities
on the coastlines. More specifically, mangroves can avert damage by decreasing the height and
energy of waves as they pass through the mangrove forests. The above-ground roots
and branches diminish the height of the waves, and thus the waves lose energy,
ultimately stopping the waves emerging onto the seabed and engulfing the sediments. The
mangroves’ roots and branches also reduce wind energy, which can stop the reformation of waves.
According to reports, densely packed mangroves can half the height of a wave through just a
100 metre passage. For comparison: in an open forest where roots and branches are more sparse,
it would take 500 metres for a wave to half its height. So preservation and reforestation of these
mangroves, or plants with a similar capability, can become a great shield against upcoming floods.
Another possible solution is to learn how to live with these flood-heavy conditions, working with
nature rather than against it. For example, let’s take a look at the flood defences in
the Netherlands where one-third of the country is below sea level, and another third is at risk of
flooding. They’ve built infrastructure that works with water and manages the rising sea levels.
They do this by designing facilities like polders. Polders are bits of land below sea level that have
been reasserted from a body of water. It’s always fully or partially surrounded by an embankment
to keep the water out that comes from either the sea or a river. These polders offer a network of
drainage canals and pumps to manage water levels, by disposing of excess water, and running water
back to the sea or river to make sure that the water doesn’t run over land. Polders can
be used to protect houses, farms and factories, and thus are used a lot throughout the country.
The Netherlands also built dams and utilised sand dunes to create ways to stay dry in their swampy
land. This shows that there are ways in which we can observe nature and live alongside it.
So, the bad news is, behind its ethereal beauty, our Moon hides a power that - if just
so combined - is set to overwhelm humanities coastal settlements. However, there's always
a little bit of good news too, as knowledge is a power of its own. By understanding our plight,
we can look for solutions, both among already existing ideas, and ways forward that have yet
to be discovered. If we are to endure what is coming, it's high time to use our innate
creativity and drive to adapt and survive; to work with our planet, rather than against it.
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Thanks for watching. Want to learn about other Cycles affecting the Earth check out this playlist
here. A big thanks to my patrons and members, if you also want your name displayed proudly at the
end of every Astrum episode, check the links below. All the best and see you next time.