IMPLICATIONS FOR CLIMATE CHANGE
The pleistocene is the present ice age in which we are currently in an interglacial period. What is India’s climate like when it’s the glacial phase i.e. Pleistocene in a glacial phase?
Not much different from now.
The ice during an ice age is all in Europe and America.
India stays more or less the same.
India’s climate hasn’t changed much in the last 2.5 million years. Nor has its geology – the current mountains and rivers were still there and the monsoon was there throughout. The Pir Panjal and Siwaliks grew higher but the big mountains of the Himalaya were only a bit shorter than now.
Ice age India is easily summarised in two lines:
1. When world gets cold, India gets dry.
2. When world gets hot, India gets wet
That just about sums up everything. For brevity the entire Pleistocene can be evaluated together ignoring the interstadials like Eemian, since it would have been similar to Holocene which contains our entire history.
Ice age landscape of India of course had some differences. Whole of Kashmir valley was a glacier during every ice age. During interglacial periods, that ice would melt completely, first forming a giant glacial melt lake in the bowl of Kashmir valley (which has been scoured out by glacial erosion). Ultimately the Jhelum and Indus would let the water in Kashmir glacial melt lake flow out, draining the lakes and making Kashmir habitable for animals, similar to the rest of the Himalayan foothills. That’s where Kashmir is presently – glaciers all drained out
Sometimes the glaciers from Kashmir would extend out into Pakistani Punjab and upper Indus region when the world got really cold and would recede back when temperatures rose. The Indus and the rivers of Punjab were exactly the same perennial rivers as they are now, as is the Ganges, throughout the ice ages.
Monsoon started a long time before the Pleistocene started. The pliocene which came before the pleistocene had whole of India drenched in rain, full of greenery and animals. When Pleistocene started, rain reduced gradually. The early pleistocene for about a million years being very wet in India. Later on in the Pleistocene ice age, i.e in the last million or so years, the world got even colder and India got drier and drier. Essentially, rainfall would show intense summer monsoon during interglacial phase and less intense monsoons during glacial periods.
In the Western ghats, it rained for longer periods during the glacial periods, upto 9 months instead of the present 4 months.
But that’s as a whole. To reconstruct the climate of India we need to focus more locally. Maharashtra and the south were lush tropical rainforests similar to what Kerala is today, during the glacial phase. Bengal and Assam were also lush tropical rainforest. It rained a lot in those places and nothing much changes in last 2.5 million years and more, whether it was glacial phase or interglacial phase.
UP and Bihar were drier places than now. The monsoon was weaker in the north than in the south during the glacial phase, though of longer duration. Most precipitation was in South India and Bengal and little reached north. The vegetation of UP was a lot lighter than in the recent past and was mostly a grassland savannah rich in herbivores.
In fact the majority of the North India plain is derived from alluvial deposits eroded and deposited from the Eemian interglacial period 130,000 years ago when the himalayan glaciers melted and flowed out, carrying the rich soil. We really dont know too much about the plains before the Eemian period because everything is burried under very thick alluvial soil. After that phase of deposition of soil got got over, UP and Bihar were initially a forest during the Eemian interglacial period.
In the Eemian as with the Holocene, the Punjab UP Bihar plains followed the same pattern - first its full of himalayan glacial melt carrying soil from Himalayas which deposits in the plain. Then a grassland grows, then denser vegetation and then thick Terai type forest grows. As long as the hot interglacial phase lasts, the plains are thick forest. As the world cools with onset of glacial phase, the monsoon reduces. The forests give way to more open woods as rainfall in insufficient to maintain it, and then scrub land comes and finally the entire north indian plain changes into a savannah grassland - it grows after the light monsoon in August and then dries out into a semi arid scrubland for the rest of the year. Most of these changes in vegetation occurred in the same fashion in Eemian and the present Holocene post 11000 BC to 500 BC - at which point we humans cut the forests and grew crops. Without humans the entire UP Bihar would be dense Terai forest. If we stop agriculture, within 100 years the plains would again be the same Terai forests.
Punjab, Sindh and Rajasthan showed the most changes during Pleistocene. It was very dry and covered by light scrub. Essentially a desert except for the Indus and other punjab river banks. As glacial melt rivers, without significant monsoon, the land between the rivers was very dry, rather similar to the present day Thaal desert of West Punjab adjacent to the upper Indus but even drier.
In other words, after the Yamuna changed direction of flow from Rann of Kutch to flow East to join the Ganges (44,000 BC) and after the monsoon reduced in the Bronze age cool period (1800 BC), the Punjab (without irrigation) demonstrated exactly how the whole of North India is during the ice age Glacial period - very dry semi arid scrub land with light monsoon in August after which the plains become a grassland but dries out over winter. The temperatures are approximately same as the present day - slightly longer winter cool period till April, less rain and Kashmir of course is iced throughout.
Gujarat had two western flowing rivers coming from the Himalayas in the ice ages. That’s what made those two estuary cuts that we are all so familiar with. The Yamuna which currently joins the Ganga flowed west but around 50,000 years ago due to gradual upliftment of the ground (Delhi ridge) it changed course and flowed east instead of west. Tothe left of the Yamuna was the Gaggar Hakra which was also a full flowing glacian melt river of the ice ages. After the Holocene hot period, the Gaggar Hakra still flowed until about 4400 years ago when reducing rainfall caused flows to reduce. The glacial melt part of the Gaggar Hakra water source changed course and was captured by the Sutlej, after which Gaggar Hakra became a dry channel which only flowed in the monsoon. After that shift, there was no other large glacial melt river east of the Sutlej, since Yamuna was already flowing West from 50,000 years ago.
A new study has demonstrated that the Gaggar Hakra was a glacial melt derived river from 80,000 to 20,000 years ago. Like the other Indus system rivers, it dried up at the last glacial maximum 20,000 years ago and became monsoon fed dry channel (like now). But from 9000 to 4500 years ago it was having good glacial melt flow because the Sutlej flowed into it at that time. 4500 years ago Sutlej changed course into the Ravi and Gaggar Hakra became a dry monsoon rain channel.
Because of these reasons, the Gujarat and Punjab were largely semi arid desert from 1800 BC until 1870 AD when irrigation from rivers and tubewells transformed these geographies.
While the Eemian was the largest interglacial period, the sediment analysis showing increased water and sediment 80,000 years ago and 45000 years ago indicate periods of relative warming in India. Though not major interglacials, they would have coincided with solar maxima due to Milankovitch cycles. Assuming 130,000 was a maximum then 80,000 is next to next maximum. 53,000 would also have been a maximum, though the changes might have taken time to affect and sedimentation might have been more in 45,000. The tilted axis is responsible for a hot period every 26000 years. But not all hot periods are as hot as the Eemian and Holocene which melted the Himalayan glaciers.
Throughout the ice age India was mostly dry and a poor place for humans to survive. The Indus region, Narmada and Tamil Nadu shows numerous Acheulean stone implements indicating presence of Homo erectus. A single skull cap of Homo erectus is also recovered from Narmada.
More advanced stone implements in Tamil Nadu might indicate migration of Homo heidelbergensis as well, 400,000 to 100,000 years ago. No fossils have been found however. Homo sapiens remains from Pleistocene are also scare to come by, though paleolithic stone tools have been found in many sites prior to 9000 BC.
The late pleistocene was therefore the worst it could get for India but it wasn’t that bad. There was adequate rain. Most of India could support rich animal life. Punjab Rajasthan and Sind were deserts in the ice age though cooler. UP and Bihar were drier but the south and Bengal were wetter.
The changes in the Holocene from 9000 BC reflect similar changes in the Eemian. With warming, the glaciers melted. The monsoon became much wetter. From 9000 to 6000 BC saw very heavy rains in the whole of India with much higher monsoon precipitation. The desert of Punjab Sindh Rajasthan and Gujrat became lush forests. Enormous sediments were carried down from the Himalayas, just as it had happened in the Eemian. The Savannah of UP and Bihar transformed into dense jungle as did the whole of Bengal and Peninsular India. 6000 to 3000 BC the rains reduced in intensity in Punjab and Western India. Vegetation became lighter Savannah grass ideal for agriculture. Neolithic and chalcolithic agriculture came up in the Indus valley civilization. UP and Bihar remained jungles as did Narmada and the south. Between 3000 and 2000BC the glacial melt flow into Gaggar Hakra switched channels to Sutlej but monsoon was heavy enough to have sufficient flow so the Bronze age civilization of IVC flourished from 2600 to 1800 BC.
Temperatures in the Holocene were pretty steady from 9000 BC on. After the maximum temperature in 9000 BC it cooled a bit post 7000 BC. That coincided with the reduced rain in Punjab. Around 2000 BC it got very cold and a mini ice age started. By 1800 BC there was much higher glaciation in North America and Siberia. Rains all over middle East reduced drastically. Egypt, Mesopotamia, Iran, BMAC and IVC faced drastic declines from 1800 to 1500 BC. BMAC and IVC vanished. Punjab, Sind, Rajasthan and Gujarat turned into deserts. Deccan and South India had reduced rainfall and turned more arid. But monsoon continued in UP and Bihar which remained forested. Post 1500 BC earth warmed again and monsoon rain in UP and Bihar and peninsular India increased and things became similar to the present day conditions.
A second mini ice age from 1200 to 1800 again saw reduced rainfall in India and population maxima reached in Pala empire in 900-1000 AD declined by almost 25-30% during the Delhi Sultanate. 1400-1500 and 1700 -1800 AD time periods were especially cold and India had repeated drought and terrible famines.
So in all probability, India has the least to fear from climate change. Europe and North America there can be drastic change with both warming and cooling eventualities. India however is likely to remain hospitable just like Africa and things will go on regardless without change. Floods and cyclones might increase, monsoon failures might increase. But those are already a feature of Holocene. We also have very little to fear from rise in sea level – which was 6 to 9 meters higher in Eemian without substantial change in India.
Pakistan, Bangladesh and China have much more to fear from climate change than India
Do check out these references:
https://www.sciencedirect.com/science/article/abs/pii/S0031018213004732
https://www.researchgate.net/publication/279705200_Late_Quaternary_history_of_the_Ganga_Plain
https://www.sciencedirect.com/science/article/abs/pii/S1040618213002139
https://sp.lyellcollection.org/content/342/1/153?ck=nck
https://www.persee.fr/doc/paleo_0153-9345_1981_num_7_1_4291
Early pleistocene fossils in Punjab Siwaliks https://go.gale.com/ps/anonymous?id=GALE%7CA524976542&sid=googleScholar&v=2.1&it=r&linkaccess=abs&issn=00309923&p=AONE&sw=w
Eocene punjab little pleistocene in jap https://www.jstage.jst.go.jp/article/jgeography1889/85/6/85_6_311/_article/-char/en
https://www.sciencedirect.com/science/article/pii/S1631068305001272
https://www.sciencedirect.com/science/article/abs/pii/S0037073813000821
https://www.pnas.org/content/early/2012/05/24/1112743109.abstract
https://www.nature.com/articles/s41598-019-53489-4
https://en.m.wikipedia.org/wiki/Balangoda_Man
https://www.britannica.com/place/India/The-Indian-Paleolithic
Man changing rivers https://www.mdpi.com/2571-550X/1/3/21/htm
