A study published in Geophysical Research Letters of the American Geophysical Union (AGU) says that due to the significant melting of glaciers because of global temperature rise, our planet’s axis of rotation has been moving more than usual since the 1990s.
GS-III: Environment and Ecology (Pollution Control and Management, Environmental Degradataion, Impact of Climate Change), GS-I: Geography (Important Geophysical Phenomena)
Dimensions of the Article:
- Is Earth’s Axis of rotation fixed?
- Is the Change in axis due to climate change similar to Precession?
- Cataclysmic pole shift hypothesis
Is Earth’s Axis of rotation fixed?
- The Earth’s rotation axis is not fixed in space – Like a rotating toy top, the direction of the rotation axis executes a slow precession with a period of 25,800 years.
- Hipparchus first estimated Earth’s precession around 130 BC – Precession is a slow rotation of the Earth’s axis around an axis perpendicular to the ecliptic plane.
- due to a combination of the Earth’s non-spherical shape and the gravitational tidal forces of the Moon and Sun applying torque as they attempt to pull the equatorial ‘bulge’ into the plane of the ecliptic.
- Precession causes the position of the Equinoxes against the background stars to gradually change, with a cycle of 25,800 years.
- The Earth’s precession implies that although Polaris is currently the star above our North Pole, in about 13,000 years, Vega will become our North star, only after yet another 13,000 years, will our North Pole will once again point towards Polaris.
- It is noted that Precession has no effect on the inclination (tilt) of the plane of the Earth’s equator (and thus its axis of rotation) on its orbital plane.
- It is 23.5 degrees and precession does not change that.
Is the Change in axis due to climate change similar to Precession?
- No. Precession here, is the change in axis with respect to outer-space as a normal phenomenon. However, the change due to melting of glaciers that is talked about in the research paper is that of the shift in location of Poles on the Earth.
- The locations of the North and South Poles are not fixed. Earth’s spin axis – an imaginary line that passes through the North and South Poles – is always moving, due to processes scientists don’t completely understand. – The way water is distributed on Earth’s surface is one factor that causes the axis, and therefore the poles, to shift.
- According to NASA, data from the 20th century shows that the spin axis drifted about 10 centimetres per year. Meaning over a century, polar motion exceeds 10 metres.
- Generally, polar motion is caused by changes in the hydrosphere, atmosphere, oceans, or solid Earth. But now, climate change is adding to the degree with which the poles wander.
What the Study says?
- According to the study melting glaciers redistributed enough water to cause the direction of polar wander to turn and accelerate eastward during the mid-1990s.
- The Earth’s axis of rotation is the line along which it spins around itself as it revolves around the Sun. The points on which the axis intersects the planet’s surface are the geographical north and south poles.
- The Earth spins around an axis kind of like a top, if the weight of a top is moved around, he said, the spinning top would start to lean and wobble as its rotational axis changes. The same thing happens to the Earth as weight is shifted from one area to the other.
- The study authors believed that this water loss on land contributed to the shifts in the polar drift in the past two decades by changing the way mass is distributed around the world. – While ice melting is the major factor behind increased polar motion, groundwater depletion also adds to the phenomenon. As millions of tonnes of water from below the land is pumped out every year for drinking, industries or agriculture, most of it eventually joins the sea, thus redistributing the planet’s mass.
- While this change is not expected to affect daily life, it can change the length of the day by a few milliseconds, experts say.
- The calculations were based on satellite data from NASA’s Gravity Recovery and Climate Experiment (GRACE) mission as well as estimates of glacier loss and groundwater pumping going back to the 1980s, according to Science Alert.
Cataclysmic pole shift hypothesis
- The cataclysmic pole shift hypothesis suggests that there have been geologically rapid shifts in the relative positions of the modern-day geographic locations of the poles and the axis of rotation of the Earth, creating calamities such as floods and tectonic events.
- There is evidence of precession and changes in axial tilt, but this change is on much longer time-scales and does not involve relative motion of the spin axis with respect to the planet.
- However, in what is known as true polar wander, the solid Earth can rotate with respect to a fixed spin axis – Research shows that during the last 200 million years a total true polar wander of some 30° has occurred, but that no super-rapid shifts in the Earth’s pole were found during this period.
- According to a study published by the Geological Society of America Bulletin – between approximately 790 and 810 million years ago, when the supercontinent Rodinia existed, two geologically rapid phases of true polar wander may have occurred. In each of these, the magnetic poles of the Earth shifted by approximately 55° – from a large shift in the crust.
- While there are reputable studies showing that true polar wander has occurred at various times in the past, the rates are much smaller (1° per million years or slower) than predicted by the pole shift hypothesis (up to 1° per thousand years). Data indicates that the geographical poles have not deviated by more than about 5° over the last 130 million years, contradicting the hypothesis of a cataclysmic polar wander event.
-Source: Indian Express