Indian Scientists Trace Harappan Decline Through Ancient Pollen Records
Source: PIB
GS I: Ancient Indian History
Overview
- Indian Scientists reconstructed past Indian Summer Monsoon (ISM) variability using fossil pollen preserved in the sediments of Deoria Tal in the Garhwal Himalaya.
- The study links climate changes with the decline of the Harappan Civilization and the migration of populations towards the eastern Ganga plains.
- The findings improve understanding of long-term monsoon variability and demonstrate how pollen records can be used to reconstruct past climate and environmental changes.
Why in the News?
Scientists from the Birbal Sahni Institute of Palaeosciences (BSIP) have used pollen records to reconstruct past monsoon variability.
News in Brief
- The Study reveal climate link behind the decline of the Harappan Civilization.
- It highlights how weakening of the Indian Summer Monsoon (ISM) influenced vegetation, agriculture, and human settlements.
- The findings improve understanding of long-term climate change and can support future climate adaptation strategies.
Key Highlights
Pollen-based Climate Reconstruction
- BSIP analysed a well-dated sediment core from Deoria Tal (Lake) of Garhwal Himalaya using 10 AMS radiocarbon dates to reconstruct vegetation and monsoon history from the mid-Holocene to the present.
- Fossil pollen and spores served as proxies for understanding past vegetation, hydroclimate, and monsoon variability.
Evidence of the 4.2 ka Climate Event
- The study identified a significant shift in the Oak–Pine pollen ratio around 4,250 years BP, indicating an abrupt dry climatic phase known as the 4.2 ka event.
- This event coincided with a weakened Indian Summer Monsoon.
- Drivers of Monsoon Weakening are,
- Southward shift of the Inter Tropical Convergence Zone (ITCZ).
- Strong El Niño conditions.
- Negative phase of the Indian Ocean Dipole (IOD).
- Reduced Northern Hemisphere summer insolation.
Other Climate Phases Identified
- Roman Warm Period and Medieval Climate Anomaly were associated with stronger monsoons due to favourable climatic conditions.
- Little Ice Age witnessed weaker monsoons because of shifts in atmospheric circulation, including ENSO, the North Atlantic Oscillation (NAO), and ITCZ.
Impact on the Harappan Civilization
- Due to weak monsoon conditions reliable seasonal flooding of the river system around the edge of the Thar desert disappeared.
- This led to migration of population residing along the Indus River and the Ghaggar-Hakra River of Indus Valley Civilization (IVC) or Harappan Civilization to new areas of the east Ganga plains for domestic and agricultural use.
- The resultant environmental stress is believed to have contributed to the shrinking of the Harappan Civilization.
Recent Pollen Studies
- Decoding India’s Farming Past
- The Study- Researchers established region-specific biometric thresholds to separate cultivated cereal pollen from wild grass pollen in the Central Ganga Plain.
- The Findings- Cereal pollen typically exceeds 46 µm in diameter and 9 µm in annulus size, whereas wild grasses fall below these marks.
- Utility- Helps archaeologists trace ancient agriculture, deforestation, and human settlement patterns. Read the details on the Press Information Bureau release.
- Ancient Monsoon Records via Lake Sediments
- The Study- Conducted by the Birbal Sahni Institute of Palaeosciences (BSIP) using sediment cores from Chhattisgarh’s Raja Rani Lake.
- The Findings- Unusually strong Indian Summer Monsoons were identified during the Medieval Climate Anomaly (1,060 to 1,725 CE) based on dominant tropical deciduous forest pollen assemblages.
Significance
- Strengthens understanding of the relationship between climate change and ancient civilizations.
- Provides insights into long-term Indian monsoon variability.
- Supports climate research and evidence-based adaptation planning.
Conclusion
The study highlights the close relationship between climate variability and human civilizations, showing how changes in the Indian Summer Monsoon shaped the trajectory of the Harappan Civilization.
It also demonstrates the value of palaeoclimate research in improving our understanding of past environmental changes and strengthening climate resilience for the future.
Key Takeaways
UPSC Prelims and Mains Practice Question
With reference to the recent pollen-based climate study, consider the following statements:
- Fossil pollen can be used to reconstruct past vegetation and climatic conditions.
- The study attributes the weakening of the Indian Summer Monsoon around 4.2 ka BP to factors including El Niño and a southward shift of the ITCZ.
- The study concludes that the Harappan Civilization expanded westward during the 4.2 ka climate event.
Which of the statements given above is/are correct?
A. 1 and 2 only
B. 2 and 3 only
C. 1 and 3 only
D. 1, 2 and 3
Answer: A
Mains Practice Question
Q. “Climate change has played a significant role in shaping the rise and decline of ancient civilizations.” Discuss in the context of the recent pollen-based study on the Harappan Civilization. (150 words)
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