A recent study by researchers at the Indian Institute of Technology, Kharagpur (IIT-KGP) has revealed that abrupt changes in the Indian monsoon in the last 900 years decided the history of the Indian subcontinent.
- The rate at which today's climate is changing is unprecedented in the geological record.
About Indian Summer Monsoons
- The onset of India's summer monsoon is linked to heat differences between the warmer land and the cooler ocean, which causes a shift in the prevailing wind direction.
- Winds blow over the Indian Ocean, picking up moisture, which falls as rain over the subcontinent from June to September.
- The monsoon season can bring drought and food shortages or severe flooding, depending on how much rain falls and in what duration.
- Incredibly dynamic system: Though confined to the tropics, the system is sensitive to climatic conditions in both hemispheres.
- Role in contributing to methane emissions: A study showed that the Indian summer monsoon pulled heat and moisture into the northern hemisphere when Earth was entering a warmer climate around 130,000 years ago. This caused tropical wetlands to expand northwards – habitats that act as sources of methane, a greenhouse gas. This amplified global warming further and helped end the ice age.
The monsoon rains of yesteryear
- Over the last one million years, the climate fluctuated between a cold glacial – known as an ice age – and a warm interglacial as the Earth's position relative to the sun wobbled in its orbit.
- The last transition from an ice age into the warm climate of the present interglacial – known as the Holocene – occurred around 18,000 years ago.
Findings of the study: Role of the climate in socio-economic conditions in the Indian subcontinent
It highlights three phases in the 900-year stretch — Medieval Climate Anomaly from 950 CE to 1350 CE, Little Ice Age from 1350 CE to 1800 CE and Current Warm Period from 1800 CE till today.
- It highlights strong monsoon during Medieval Climate Anomaly and Current Warm Period and phases of weak and strong monsoon in Little Ice Age.
- Deficient rainfall led to the collapse of the Mansabdari system, started by Mughal emperor Akbar, in the late 17th century.
- Similarly, drought interspersed with violent monsoon rains sounded the death knell for the Khmer empire of south-east Asia in the 15th century.
- Several dynasties, such as the Sena in Bengal, Solanki in Gujarat in the mid-13th century and Paramara and Yadav in the early to mid-14th century – all of which flourished during abundant rainfall — declined during the dry phases of the Indian summer monsoon (ISM).
- Recent phases of human history: from the beginning of the 19 century, the changes in the ISM became more abrupt with a rise in atmospheric temperature that coincides with the dawn of the Industrial Revolution.
How the study was conducted?
- Experts from Wadia Institute of Himalayan Geology (under the Department of Science and Technology, Ministry of Science and Technology), looked at palaeoclimatic records using oxygen isotope proxy record from speleothems (a structure formed in a cave by deposition of minerals from water) at the Wah Shikar cave in Meghalaya.
- Samples from every half millimeter or less were dated using uranium-thorium time series. Such a fine sampling of less time interval means that data at two-three years’ interval was analyzed.
About Uranium-Thorium dating
- It is a way of determining the age of a rock by the amount of radioactive Thorium it contains.
- This method can be used to determine the age of calcium carbonate materials, such as coral.
- Scientists can measure the amount of Thorium-230 in a sample of rock if the rock contained Uranium originally.
- Uranium is often found in trace amounts in certain types of rock and is radioactive.
- It has a half-life (the amount of time it takes for the radioactivity of the element to decrease by half) of about 245,000 years.
- At this point, it undergoes alpha decay (it releases an alpha particle, which is also the same as the nucleus of a Helium atom) and forms Thorium-230.
- Thorium has a much shorter half-life of 75,000 years.
- Unlike other types of radioactive dating, Uranium-Thorium (U-Th) dating doesn't reach a stable endpoint.
Significance of study: Climate change and its impacts
- An increase in the frequency of abrupt shifts in the ISM during the last three centuries, coincidental with a rise in atmospheric temperature, suggests a future rise in the global temperature and subsequently more precipitation in the form of rain at higher altitudes.
- Being able to reliably predict summer monsoon rainfall is critical to plan for the devastating impact it can have on the 1.7 billion people who live in the region.
- Akbar introduced this Mansabdari system in 1571.
- The mansabdari system was an improvement over the systems of tribal chieftainship and feudalism; it was a progressive and systematic method adopted by Akbar to reorganize his army within the fold of despotic monarchy.
- The gazetted imperial officers of the state were styled as Mansabdar’s.
- The broad outlines of the system have been given by Abul-i-fazl in the Ain-I Akbari.
- Mostly the recruitment of the mansabdars was made on the recommendation of the mirbakshi who presented the person to the emperor.
- Under the mansabdari system, different number’s which could be divided by ten were used for ranking officers.
- The mansabdari system put an end to the jagirdari system within the territories under the direct control of the imperial government.
- No portion of a manual was hereditary, and a mansabdar’s children had to began afresh.
Source: Medieval India History by Romila Thapa