When looking at world maps it is easy to point to the fixed geographic North Pole where all the world's longitudinal lines converge, but the magnetic North Pole is another matter, it currently wanders around 55km annually, now moving faster than pre-2018 records according to the U.S. National Oceanic and Atmospheric Administration (NOAA). Similarly the magnetic South Pole also has an historic tendency to wander.
However in recent decades the sheet ice melt that is changing Greenland, the Arctic and Antarctic has added another twist to the story.
The annual cycle of daylight length is also changing. This is of more than passing interest as human physiology and behaviour are shaped by the Earth’s rotation around its axis and the human brain responds to light changes in the environment.
The Guardian, 16 July 2023:
The climate crisis is causing the length of each day to get longer, analysis shows, as the mass melting of polar ice reshapes the planet.
The phenomenon is a striking demonstration of how humanity’s actions are transforming the Earth, scientists said, rivalling natural processes that have existed for billions of years.
The change in the length of the day is on the scale of milliseconds but this is enough to potentially disrupt internet traffic, financial transactions and GPS navigation, all of which rely on precise timekeeping.
The length of the Earth’s day has been steadily increasing over geological time due to the gravitational drag of the moon on the planet’s oceans and land. However, the melting of the Greenland and Antarctic ice sheets due to human-caused global heating has been redistributing water stored at high latitudes into the world’s oceans, leading to more water in the seas nearer the equator. This makes the Earth more oblate – or fatter – slowing the rotation of the planet and lengthening the day still further.
The planetary impact of humanity was also demonstrated recently by research that showed the redistribution of water had caused the Earth’s axis of rotation – the north and south poles – to move. Other work has revealed that humanity’s carbon emissions are shrinking the stratosphere.
“We can see our impact as humans on the whole Earth system, not just locally, like the rise in temperature, but really fundamentally, altering how it moves in space and rotates,” said Prof Benedikt Soja of ETH Zurich in Switzerland. “Due to our carbon emissions, we have done this in just 100 or 200 years. Whereas the governing processes previously had been going on for billions of years, and that is striking.”
Human timekeeping is based on atomic clocks, which are extremely precise. However, the exact time of a day – one rotation of the Earth – varies due to lunar tides, climate impacts and some other factors, such as the slow rebound of the Earth’s crust after the retreat of ice sheets formed in the last ice age.
These differences have to be accounted for, said Soja: “All the datacentres that run the internet, communications and financial transactions, they are based on precise timing. We also need a precise knowledge of time for navigation, and particularly for satellites and spacecraft.”....
