 Hello and welcome to NewsClick. Today in Talking Science and Tech, we will be looking at new research on climate shifts, which can help further our understanding on how ancient civilizations in Asia and Africa may have collapsed. And to talk about this, we have with us Prabir Prakash Sita. So Prabir, can you first tell us about this new study, new research, which looks at the megadrots which occurred in Southeast Asia 5,000 years ago? It's an interesting question what you're asking because I think the studies in fact do show that weather patterns had an enormous impact on civilizations in this period. There have been a number of studies which had earlier suggested this and this is in fact continuation of the method used earlier to declare the megalayan period itself, which was that 4,200 years back there were megadrots in different parts of the world and the record of that, confirmation of that was the stalagmites that were studied in a megalayan cave and they found that you could clearly distinguish that the showers, the rainfall had reduced because the oxygen isotope, the light oxygen isotope which is there in bigger showers were less than the age, sorry, oxygen 18 isotope which is heavier, which normally falls in the lighter showers or in the pre showers. So this identification of how much rainfall using stalagmites, using the taking cores out of that trying to see what is the oxygen isotope levels of the two isotopes of oxygen, all of that is something which led to the declaration of the megalayan period itself and this is what is now being used in the different parts of the world to see what is the rainfall pattern and can we relate certain historical events to such patterns. Now there have been certain anomalies, in fact, this particular study points it out that you would expect agriculture to have sprung up in Southeast Asia in this period because it is there in other parts of the world, but you do not find it in Southeast Asia in this particular period, so what is it due to? So initially it was felt that maybe it is because people really have not found the sites of ancient agriculture, now they are coming around to the view that agriculture would have collapsed because of the mega drought that took place and they have identified a long period of this drought. Now these researchers, unlike the other ones who have talked about this similar droughts in North India for instance, essentially the Kala collapse of the Mohan Dharav civilization, the Harappan civilization and also in South, in West Asia and North Africa, Egyptian collapses in this period, the Akkadian Empire collapsing and also in fact in what is the Anatolian Peninsula, the Hittites, so there have been records at different points of research of seeing collapse of civilizations or roughly around the same time, so the question has been is it related to a climate event and this seems to suggest that it is except this says the climate event was much longer, while you take the other places into account it's quite possible in those places there was not a 1500 years or 800 years long climate event, but it was of a shorter duration which is really 200 years. That's also because the way the weather patterns in these places move that we have really three very large weather, you know, climate patterns that exist. One is essentially over the Atlantic which is also connected to for instance the ocean currents and you get as you know the what's called the Endino or Southern Oscillations because of that, then you have the Monsoons and Indian Monsoon is of course the very big part of that, that's a very particularly it also affects the two hemispheres, Southern and Northern Hemispheres and then you have the East Asian Monsoon, Southeast Asian East Asian Monsoons, so these are the really very large climate events that takes place, the pattern that takes place which determines also how you are going to see rainfall or other temperatures in this region. So it does seem that they are correlated but they may not be as strongly coupled meaning that if something happens for 200 years over West Asia and North India, it does not mean that it happens for the same duration in China or in Southeast Asia but there are close couplings, that means there is the effect but it may be not identical. So it seems to be if we look at the data that we are getting that we have a large mega-route which took place in Southeast Asia probably in South China as well, Yangtze being affected, then you had sharper but shorter periods in these parts of the world because you don't see such a long route being recorded and these are all records, after all Egyptians kept very good records, in fact the Egyptian Empire did not collapse unlike the Akkad then or Mohanjidaro basically the urban civilization disappearing, so such cataclysmic changes did not take place in Egypt though yes the urban civilization there did take a big hit. So if we take all the recorded evidence we see some commonalities but some differences too, so it does seem to be that yes climate had a big role to play in these changes for us to understand because till now we have been thinking it's only overthrow of settled agriculture could only take place if some people come and overthrow these people so destroy the basis of the agriculture itself and Mohanjidaro Harappa has been something of an anomaly that we didn't understand why it had collapsed. Now if we look at this picture and it's across a large part of the world then we can see that yes this failure of understanding is because we did not think the civilizations were so brittle that a small climate shift could lead to a significant change in the way people live so therefore it's also an indication of how narrow the surplus was to maintain the cities that if for instance crop productivity falls by 10 percent maybe cities are not then they cannot survive because that's what determines or really drives the urban population so urban civilization can only survive if there is surplus from the farming population to the urban centers and that means there must be at least a surplus that you can produce the farmers can produce which then can go to others so that that brittle nature of these civilizations when the surface is very narrow and it would seem to indicate that but I think this is a very interesting study because we are now trying to relate very dissimilar disciplines together to understand our past and also the researchers in the study are pointing out that how this could all be linked to one major event which was the gradual desertification of North Africa of the Sahara which used to be very green but we know now it's a desert so can you tell us about that how those two ends are linked? Yes the green Sahara issue that Sahara was not a desert it was relatively green and at some point there is a temperature there is a climate change of some kind which leads to northern Africa largely becoming desertified so in fact that's the end of green Sahara. Now why did that happen? I don't think we have still received any clear explanations of that but we know that it did happen so that that much of information we have so one of the things that would happen and this is what these researchers have said that that would lead to certain changes between how moisture bearing winds then would operate in the in this part of the world along the tropics and this lack of enough moisture coming would mean the weakening of the rain bearing winds and so on and so forth but I think there's one thing important to remember that in large parts and this is really seems to seem to be around the tropics this whole region which is affected seems to be around the tropics. Now it is more in large parts of it as we said it seems to be a 200-year event so if it was greening of the loss of greenery in Sahara if it was left to that I think we would have seen a different configuration of the climate in this entire region it cannot be that it only affects us for 200 years and then it comes back to the pre situation when there was the rainfall is restored so you can see a break on a 200-year drought scenario now there are two ways of explaining it one there is something ma which massive which is shifted and that has created a 200-year hit on the climate before it comes back that's one possibility the other possibility is that that's a quite a dangerous possibility that we have a bi-stable system which periodically can shift so the major part of it it is in the mode that we see today but there is because the bi-stable system it can fall into a pattern which creates a stable weather pattern which is different and that different weather pattern would be much less rains in the tropics the places that we have talked about from Southeast Asia Southern China to Northern India to West Asia if that is true then it is possible to flip the weather back flip the climate back to this situation where we again get mega drought so if we for instance look at climate change today the fact that we are the largest drivers of climate change with the amount of carbon dioxide we are putting in the atmosphere so it is possible that because the climate is you know the climatic system so to say has a huge inertia and therefore normal human activity would not shift the climate system from one stable stable for configuration to another but that it did do it at one point of time whatever may be the reason means it can do so again so I think that is something that is something for all of us to consider but looking at it and looking at the fact that the green Sahara I don't see green Sahara being directly connected to the 200 year mega drought that 200 years of mega drought we are talking about it could be connected to a major shift of the climate could be possibly and that that a different stable system to emerge took time and therefore the 200 drought that we are talking about really takes takes at the end of this climate pattern shifting and this was a you know a some in some sense a closing chapter of a large shift of the climate the problem with this formulation and I think the experts have to debate this out is that we should have seen also precursor to that slow change over North India for example or over West Asia before such a climb you know climactic change takes place when this 200 years of mega drought takes place so somehow I'm not I'm not sure that this is perhaps explanation so I think you have really because of the three systems which are connected something that happens over the North South Atlantic which has an effect of North on man North Africa then you have the the monsoon systems one the Indian monsoons the East East Asian monsoons so all these three system and the interact there could be changes which are introduced which we need to understand in totality so it's possible that Southeast Asia the 1500 year drought which is what these researchers are talking about could be the result of the green Sahara ending but I don't think it explains the 200 year droughts that we talk about in this particular case which took place in North India and West Asia Egypt that I don't think is that easy to explain so it's quite possible that the East Asian monsoon the North Atlantic climate system all of that have a more complex interaction so I think it's really a matter of now more research to see a much greater detail and also the climate models we can now build and hopefully solve to see what what is a possible answer to this now three mysteries which have seemed to be connected together one is this 1500 year mega drought over Southeast Asia I don't know how long it was over China South China it seems to have been also been affected also Korea for instance has come into this discussion in some form then of course what is the impact over from North Africa to India Southeast Asia to be accurate and also what led to the green Sahara being destroyed so all these things now are puzzles which seem to be connected together so I think it's exciting times because you were seeing new methods you were seeing modeling being used you are seeing different kinds of disciplines being put together for essentially paleo history ancient history earlier we really looked at artifacts and to understand history now we're looking at much larger issue you know much larger set of variables and I mean that's a very exciting time to be in to see how can explain distant past with all the tools we have not just what the archaeologists or the historians have used and you know to end it all there has been this debate that the megalian period this side suddenly identification of this new period is going against the whole bunch of people who said we should really describe something called the Anthropocene period which is a human activity the one where the human beings have changed the what is in the you know the climate as well as the world so this change needs to be registered as we are now the biggest element of changing climate as well as the habitat so this debate now needs to be refined somewhat to show that actually in this period it still is that much larger forces are at work and relative to that we were not so important so I think it does show that the geological age being determined and the errors being determined based on measurable climate events so to say in this particular case it meant that each age had some physical things that you could measure this is 66 million years back and therefore you know this event took place that's how we have dated our various errors and this particular this particular event is also then connected to something which is physical you can measure the change of oxygen isotopes in rainfall which you are measuring so it's a physical measurement you can do so till this point you are also privileging natural phenomena in terms of the turbulent epochs and not the human phenomena so I think that is still holding true for this period is I think an interesting interesting development that yes of course this is Anthropocene era there is no question this is very much there but nevertheless still it's predominantly to be seen in terms of various geological ages that we have given we still have to continue looking at this period also in those terms because after all here is the change point taking place now we are going to be far more important in determining what's going to happen on the surface of the show thank you for being for talking to us today and that's all the time we have keep watching news click