09 July 2021

The 18.6-year Lunar Nodal Cycle: What it is and why it matters

"Right now, we’re in the phase of an 18.6-year lunar cycle that lessens the moon’s influence on the oceans. The result can make it seem like the coastal flooding risk has leveled off, and that can make sea level rise less obvious."
I want to share an article that I wrote for The Conversation back in April, before an upcoming perigean full moon.  The article isn't related to hurricanes, but to another topic that I have an interest in: sea level rise.  I hope you don't mind this brief excursion.  Of course, water levels and hurricanes do share one thing in common: storm tide, the combination of the "normal" tide level and storm surge.  So perhaps this is more of a tangent than an excursion?

The topic is the 18.6-year lunar nodal cycle, and the article describes what it is and why it matters.  It was first documented hundreds of years ago, so it's hardly "news".  But this very normal and regular oscillation in Earth's tides is superimposed on sea level rise, and that is becoming a bigger and bigger concern and problem around the world as the decades tick by.

"The effect of the nodal cycle is gradual – it’s not anything that people would notice unless they pay ridiculously close attention to the precise movement of the moon and the tides for decades.

[But] it’s worth being aware of this influence, and even taking advantage of it. During the most rapid downward phase of the lunar nodal cycle – like we’re in right now – we have a bit of a reprieve in the observed rate of sea level rise, all other things being equal. These are the years to implement infrastructure plans to protect coastal areas against sea level rise.

Once we reach the bottom of the cycle around 2025 and start the upward phase, the lunar nodal cycle begins to contribute more and more to the perceived rate of sea level rise. During those years, the rate of sea level rise is effectively doubled in places like Miami."

The full article is available on The Conversation:


1 comment:

  1. Actually by 2035-2045 SLR will have accelerated, so we will not get a leveling during that period, just a slower rise.