Really, how fast is the arctic circle shifting/shrinking?

Factual Questions
1

This is from Wikipedia “The position of the Arctic Circle is not fixed and currently runs 66°33′49.0″ north of the Equator. Its latitude depends on the Earth’s axial tilt, which fluctuates within a margin of more than 2° over a 41,000-year period, owing to tidal forces…Consequently, the Arctic Circle is currently drifting northwards (shrinking) at a speed of about 14.5 m (48 ft) per year.” 48 feet per year!!! That can’t be right. Can it?

2

Let’s see, in round numbers, if the obliquity of the ecliptic (i.e., Earth’s axial tilt) changes about two degrees every 20,000 years (since it takes 41,000 years to complete the cycle of fluctuation increasing by nearly 2 1/2 degrees and then decreasing back to the initial value), then it’s changing about one degree in 10,000 years, or about 21.5 arc-thirds (i.e., about one-third of an arcsecond) per year.

If the obliquity were zero, the Arctic Circle would be at its minimum size of zero, reduced to the point of the North Pole, because the sun would illuminate every latitude on earth for half of every day. If the obliquity were 90 degrees, the Arctic Circle would be at its maximum size equal to the equator, because the entire northern hemisphere would get dark.

Currently, the obliquity is decreasing, at about one-third of an arcsecond per year, as we found. That means the latitude of the Arctic Circle (which is the complement of the obliquity) is increasing at that rate.

Now, there are about 69 miles per degree of Earth’s latitude, or in round numbers about one mile per arcminute, or about 1/60 mile per arcsecond. A sixtieth of a mile is 88 feet, and a third of that is nearly 30 feet.

So, allowing for my very approximate guesstimating, my figure of about one-third of one arcsecond of latitude = one-third of one-sixtieth of one-sixtieth of 69 miles = about 30 feet for the annual change in latitude of the Arctic Circle is not that different from your source’s figure of 48 feet. So yup, I think it can be right!

3

Bravo. Thank you.

4

There’s a marker for the Arctic Circle on Grimesy Island - part of Iceland. They move it every year to reflect the movement of the Arctic circle. There are 2 problems:

  1. The Arctic circle is predicted to move off Grimesy Island by 2047.
  2. The marker is a granite sphere called ‘Orbus et Globus’ and weighs 9 tonnes.