 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. So, Prabir, can you first tell us about this new study, new research, which looks at the megadrotes 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 at 4,200 years back. There were megadrotes in different parts of the world and the record of that, the confirmation of that was the stalagmites that were studied in the 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's there in other parts of the world. But you don't 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're 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, Dharapan 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, you know, research of seeing collapse of civilizations 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 that this says the climate event was much longer. When 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, 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, what's called the El Nino or Southern Oscillations because of that. Then you have the Monsoons. I mean, 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. It 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 drought, 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 do not see such a long drought 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 den 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 still now we have been thinking it is 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 did not understand why it had collapsed. Now, if we look at this picture and it is 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 is 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 is 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 brittle nature of these civilizations when the surplus 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 now it's a desert. So, can you tell us about that, how those two events 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 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 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 is one thing important to remember that in large parts, and this 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 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 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 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 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 of 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 mean much less rains in the tropics, the places that we have talked about from Southeast Asia, Southern China, to Northern India, to West Asia. Now, 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 the climatic system, so to say, has a huge inertia, therefore normal human activity would not shift the climate system from one 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 a different stable system to emerge took time. And therefore, the 200 drought that we are talking about really takes at the end of this climate pattern shifting. And this was a, 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 climatic change takes place, when this 200 years of mega drought takes place. So, somehow 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 Africa, then you have the monsoon systems, one the Indian monsoons, the East Asian monsoons. So, all these three systems when they 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 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 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, South 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 were 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, you know, much larger set of variables. 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 Meghalayan period, this 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 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 determining epochs and not the human phenomena. So, I think that is still holding true for this period is I think an interesting development that yes, of course, this is Anthropocene era, there is no question that 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 talking to us today. And that's all the time we have. 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