Central Ideas

• A recent study conducted by scientists at Seoul National University has revealed that the extraction of groundwater from the earth has caused a shift in the planet’s axis, tilting it nearly 80 cm to the east.
• This phenomenon, along with the movement of water through melting ice caps and glaciers, has implications for both the earth’s rotation, sea-level rise, and the distribution of water resources.

Earth’s Axis and Rotation

• The Earth’s axis and rotation play significant roles in shaping our planet’s climate, seasons, and day-night cycles.
• Here are some key points about Earth’s axis and rotation:

1. Axis: The axis is an imaginary line that extends between the North Pole and the South Pole and is tilted at an angle of approximately 23.5 degrees relative to its orbital plane around the Sun. This tilt is responsible for Earth’s seasons.
2. Rotation: Earth rotates on its axis from west to east, completing one full rotation in approximately 24 hours. This rotation is what gives us the cycle of day and night. The side of the Earth facing the Sun experiences daylight, while the opposite side experiences darkness, resulting in day and night.
3. Polar Regions: The axis of the Earth is inclined with respect to its orbital plane. This inclination causes the Polar Regions to experience variations in daylight throughout the year. During the summer solstice (around June 21), the North Pole is tilted towards the Sun, resulting in 24 hours of continuous daylight in the Arctic Circle and 24 hours of darkness in the Antarctic Circle. The opposite occurs during the winter solstice (around December 21).
4. Equator: The equator is an imaginary line equidistant from the poles and divides the Earth into the Northern Hemisphere and the Southern Hemisphere. The equator experiences relatively consistent day and night lengths throughout the year, with two equinoxes occurring when the Sun is directly above the equator. During the equinoxes (around March 21 and September 21), day and night are approximately equal in length worldwide.
5. Precession (Cyclic Wobble): In addition to its axial tilt, Earth experiences a slow, cyclic wobble called precession. This wobble causes the orientation of Earth’s axis to change slightly over a period of approximately 26,000 years. Precession does not affect the tilt or the length of the seasons but does influence the positions of the celestial poles and the timing of Earth’s closest approach to the Sun (perihelion) and farthest point (aphelion).

Why in news?

• Unlike a stable rotating globe, the earth’s axis experiences a wobble due to various factors such as weather, seasonal changes, the molten core, and natural events like hurricanes.
• Scientists track this motion relative to astronomical phenomena, but the role of water movement, including groundwater extraction, had not been fully considered until now.
• The earth’s axis wobbles in a circular pattern several meters wide every year.

Study Findings

• Researchers at Seoul National University built a climate model linking the earth’s axis shift with water movement, including the melting of ice caps and glaciers.
• Initially, the model did not match the observed drift of the axis until groundwater extraction was added to the equation.
• Groundwater pumping accounted for the unexplained cause of the rotation pole drift.
• The shift in the earth’s axis due to groundwater extraction was measured at nearly 80 cm tilt to the east.

Implications for Sea-Level Rise

• The study revealed that approximately 2,150 billion tonnes of groundwater were pumped and drained into the oceans between 1993 and 2010, contributing to a sea-level rise of 6.24 mm.
• Groundwater depletion plays a significant role in the location and magnitude of the axis drift.
• Mid-latitude regions, particularly northwest India and western North America, showed the most significant groundwater redistribution effects.

Impact on Water Resources

• Groundwater extraction for human activities, including irrigation, is affecting the distribution and availability of water resources.
• Excessive groundwater pumping has led to a significant redistribution of water, altering the balance between surface water and groundwater reserves.

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