Moon Wobble

Moon Wobble

Subject: Science and Tech

Context: US coastlines will face increasing flooding in the mid-2030s thanks to a regular lunar cycle that will magnify rising sea levels caused by climate change, according to research led by NASA scientists.

A key factor identified by the scientists is a regular “wobble” in the moon’s orbit – first identified in the 18th century – that takes 18.6 years to complete. The moon’s gravitational pull helps drive Earth’s tides.

Concept:

What is moon wobble?

• The moon wobble is nothing but a regular swaying in the moon’s orbit. It was first documented way back in 1728. This wobble takes over an 18.6-year period to complete, and continues in a cyclic fashion.
• Their results underscored a basic fact separate from the movement of the moon: Our oceans are rising because of climate change.

What impact does this wobble have on Earth?

The moon wobble impacts the gravitational pull of the moon, and therefore, indirectly influences the ebb and flow of tides here on the Earth. In fact, as per the NASA study, each wobble cycle has the power to amplify and suppress the tides on Earth.

One half of the 18.6-year cycle suppresses the tides, which means that the high tides get lower, while the low tides get higher than normal. Once this cycle completes, the situation flips—in the subsequent cycle, the tides are amplified, with high tides getting higher and low tides, lower!

The lunar cycle is expected to shift again by mid-2030, and in the coming phase, the tides will amplify once again.

Moon wobble and climate change: A double whammy situation

The upcoming changes in the lunar cycle will pose a serious threat, as the amplified high tides coupled with the rising sea levels will make the risk of flooding far greater across all coastal regions of the globe.

The study predicts that the high tide-associated floods—also known as nuisance floods or sunny day floods—may occur in clusters that could last for months or even for longer periods!

This surge will be closely associated with the position of the Moon, Earth and the Sun. A NASA statement explains: “When the Moon and Earth line up in specific ways with each other and the Sun, the resulting gravitational pull and the ocean’s corresponding response may leave city-dwellers coping with floods every day or two.”

As per NOAA, episodes of such flooding are already on the rise, especially across the U.S. Atlantic and Gulf coasts. In 2019, over 600 such floods were reported from the US. With these grim projections, the flooding situation is likely to worsen, especially for people living in the low-lying regions of the globe.

Wobble formation

• High tides on this planet are caused mostly by the pull of the moon’s gravity on a spinning Earth. On most beaches, you would see two high tides every 24 hours.
• The moon also revolves around the Earth about once a month, and that orbit is a little bit tilted. To be more precise, the moon’s orbital plane around the Earth is at an approximate 5-degree incline to the Earth’s orbital plane around the sun.
• Because of that, the path of the moon’s orbit seems to fluctuate over time, completing a full cycle sometimes referred to as a nodal cycle — every 18.6 years. It happens on such a slow scale
• ‘Precession’ is a more specific word than ‘wobble.’ “At certain points along the cycle, the moon’s gravitational pull comes from such an angle that it yanks one of the day’s two high tides a little bit higher, at the expense of the other.
• This does not mean that the moon itself is wobbling, nor that its gravity is necessarily pulling at our oceans any more or less than usual.
• The emphasis on the nodal cycle is a little bit different from the message we were trying to convey.
• High-tide flooding related to climate change is expected to break records with increasing frequency over the next decade, and people who want to accurately forecast that risk have to work with a lot of noisy data, including weather patterns, astronomical events and regional tidal variation.
• The moon wobble is part of that noise, but it has always maintained its own slow, steady rhythm.
• During its most rapid upward phase, it acts to enhance the effective sea level, and during its most rapid downward phase, like we’re in now, it acts to suppress the effective sea level. It is not part of sea level rise projections because it’s not sea level rise; it’s just an oscillation.

The effect of wobble

• The effect of the wobble could cause high tide levels at a beach to oscillate by 1 or 2 inches over the course of its long cycle.
• That may sound small. But in certain situations, it can matter quite a bit.
• It just kind of raises the baseline and the more your baseline is raised, the smaller weather event you need to cause a flooding event.
• Understanding that baseline is important even when we are in the phases of the nodal cycle
• It’s important to realize that at the mid-2030s point, where the switch flips and the natural cycle seems to amplify the rate of sea level rise, then we are going to see a rapid change.