Why in News?
A study by the Birbal Sahni Institute of Palaeosciences (BSIP) has used pollen preserved in lake sediments from Deoria Tal (Garhwal Himalaya) to reconstruct past climate. The findings suggest that a prolonged weakening of the Indian Summer Monsoon (ISM) and the 4.2 ka climatic event contributed to the decline and eastward migration of the Harappan Civilization.
Key Findings
- Analysis of pollen and spores reconstructed vegetation and monsoon history over the last ~5,100 years.
- Around 4200 years BP [Before Present](4.2 ka event), the region experienced an abrupt cool and dry climate with a weakened ISM.
- Reduced monsoon weakened the perennial river systems of the Indus and Ghaggar-Hakra, making agriculture difficult.
- This likely triggered the migration of Harappan populations towards the Ganga plains, contributing to the shrinking of the civilization.
- The study establishes a strong link between abrupt climate change and changes in ancient human settlements.
How Did Scientists Reconstruct the Past?
- Sediment core collected from Deoria Tal in Uttarakhand.
- Pollen analysis (Palynology) reconstructed past vegetation and climate.
- Chronology established using 10 AMS Radiocarbon (¹⁴C) dates on Trapa (water chestnut) seed cases.
- Changes in the Oak/Pine pollen ratio served as an indicator of changing temperature and monsoon strength.
What is the 4.2 ka Event?
- A major global climatic event that occurred around 4200 years ago.
- Characterized by:
- Weak Indian Summer Monsoon.
- Cooler and drier climate.
- Widespread droughts across several ancient civilizations.
- Linked to the decline of civilizations such as Harappan Civilization, Akkadian Empire, and Old Kingdom of Egypt
Why Did the Monsoon Weaken?
Researchers attribute the weakened ISM to multiple interacting climatic factors:
- Southward shift of the Inter Tropical Convergence Zone (ITCZ).
- Strong El Niño conditions.
- Strong negative phase of the Indian Ocean Dipole (IOD).
- Reduced Northern Hemisphere summer insolation.
Other Climate Phases Identified
- Roman Warm Period (2500 to 1450 cal yr BP): Strong ISM and higher agricultural productivity.
- Medieval Climate Anomaly (1050 to 650 cal yr BP): Strong monsoon due to northward ITCZ.
- Little Ice Age (650 to 100 cal yr BP / CE 1350 to 1850): Weak ISM associated with stronger westerlies, ENSO and southward ITCZ.
[2026] Consider the following statements about the archaeological findings in Harappan towns:
I. There is wide occurrence of spindle-whorls in the houses but absence of spinning wheels.
II. Weights and measurement scales, complete with graduations have been discovered.
III. There are houses built in large part with baked bricks, around relatively spacious courtyards, with their own wells, bathing platforms, and large rooms.
Which of the following inferences can be drawn from the above statements?
1. Statement I suggests that spinning was a laborious activity done at home.
2. Statement II suggests the extent of the scientific knowledge that the Harappans possessed.
3. Statement III suggests the emergence of a common property system.
Select the answer using the code given below :
[A] 1 and 2 only
[B] 2 and 3 only
[C] 1 and 3 only
[D] 1, 2 and 3