Prelims: Current events of national and international importance | History | Science and Technology
Why in News?
Recently, A study, used pollen analysis from Deoria Tal to reconstruct vegetation and hydro‑climate variability. Findings link the shrinking of the Harappan Civilization to abrupt climate change.
Key Findings
- Conducted by – The Birbal Sahni Institute of Palaeosciences (BSIP), supported by the Department of Science and Technology (DST).
- Timeline – Weak Indian Summer Monsoon (ISM) between 5100–4000 cal yr BP.
Cal yr BP – Calibrated calendar years before the present; The present is 1950; to find the approximate historical year (BCE), subtract 1,950 from historical year. 4250 cal yr BP is around 2300 BCE.
- Evidence – Oak/Pine pollen ratio showed abrupt increase around 4250 cal yr BP, matching sedimentological records of dry climate at 4200 cal yr BP.
- Impact – Collapse of reliable seasonal flooding along Indus and Ghaggar‑Hakra rivers, hence migration started eastwards to Ganga plains.
- Cause – Cool‑dry climate, weak ISM due to southward shift of ITCZ, decreasing Northern Hemisphere summer insolation.
Methodology
- Sediment Core – Scientists studied sediment cores from Deoria Tal in the Garhwal Himalaya.
- Dating – They dated samples using radiocarbon analysis of Trapa seed cases, calibrated with OxCal software.
- Tools – Pollen and spores have been used as established tools for reconstructing past vegetation dynamics and contemporary climate change.
- Collaboration – The study involved collaboration between universities in India and the USA, using pollen and spores as indicators of past vegetation and climate.
Historical Climate Patterns
- Roman Warm Period (2500–1450 years ago) – The Indian Summer Monsoon was strong, leading to high agricultural productivity and what is called the “Golden Age of India.”
- Medieval Climate Anomaly (1050–650 years ago) – The monsoon remained strong due to a northward Intertropical Convergence Zone (ITCZ) shift, solar activity, and ENSO influence, resulting in wetter conditions.
- Little Ice Age (650–100 years ago; CE 1350–1850) – The monsoon weakened because of intensified Asian westerly jets, positive North Atlantic Oscillation, ENSO warm phase, and a southward ITCZ shift.
- 4.2 ka event – It was a major cooling phase during the Holocene period.
- It provides a natural case study to understand how the Indian Summer Monsoon was influenced by El Niño, ITCZ shifts, Indian Ocean Dipole, and summer insolation in low‑latitude regions.
Significance
- Historical – Explains Harappan decline through climate stress.
- Scientific – Demonstrates pollen as tool for reconstructing past monsoon variability.
Reference
PIB | Harappan Civilization
