Thursday, February 2, 2017

Climate Change and the Indus Valley Civilization

The Indus Valley or Harappan Civilization was at its peak between about 2600 and 1900 BCE. After that it rather mysteriously declined. The part of the world where these people lived (Pakistan and northwestern India) contains a bunch of old, dried-up river courses and lake beds, which show that it was once wetter than it is now. So as far back as the nineteenth century archaeologists argued that maybe the Indus Civilization was done in by climate change.

And there have been claims that the drying of the region happened at about the right time, c. 1900 BCE. But the science on this is very iffy, and there have been lots of other claims. The latest, coming from a major study across a wide swath of India, suggests that the greatest drying occurred around 2200 to 2000 BCE. When they announced this dating, the archaeologists involved said that they had found the cause of Indus civilization's decline.

Of course 2200 BCE is 300 years before Indus Civilization began its precipitous decline, and 300 years is a long time to hang on without enough water. So the same group of archaeologists set about figuring out how people adapted to that change. Did they grow different crops, put more emphasis on herding, extend irrigation, move to someplace wetter? No. So far as this study showed, people changed nothing at all.
We argue that rather than being forced to intensify or diversify subsistence practices in response to climatic change, we have evidence for the use of millet, rice, and tropical pulses in the pre-urban and urban phases of the Indus Civilization. This evidence suggests that local Indus populations were already well adapted to living in varied and variable environmental conditions before the development of urban centers. It is also possible that these adaptations were beneficial when these populations were faced with changes to the local environment that were probably beyond the range of variation that they typically encountered
Translated into English, that seems to mean that people did not have to change because their existing style of farming was already flexible enough to cope with a great deal of variation in rainfall.

I personally love this result, because I have gotten tired of climate change being used lazily an an explanation for every change in human society. People are adaptable, and thrive in all but the driest and coldest climates. I can imagine a scenario in which the climate continued to worsen and the early success people had adapting to declining rainfall without major changes only made them more vulnerable when things got too bad for their system to continue. But that is not what this study shows; it shows the Indus civilization sailing through what the authors identify as the period of most profound change in the climate over the past several thousand years.

I would say that leaves the relationship between the drying climate and the end of Indus Civilization as much up in the air as ever.

1 comment:

G. Verloren said...

"it shows the Indus civilization sailing through what the authors identify as the period of most profound change in the climate over the past several thousand years."

You seem to be misunderstanding how rate of change and total amount of change can differ wildly.

Certain effects don't occur until you reach a critical threshold. It doesn't matter if you go racing over a cliff at full gallop, or if you slow down to a crawl a full mile in advance, as long as you keep moving forward, no matter the rate, you're still going plummet to the bottom once you eventually go over the edge.

Looking at "the period of greatest drying" only tells you the time at which a drought was progressing most severely. But there's a difference between the rate of drying slowing, and the drying stopping or reversing. There's also a difference between reaching a peak of briefly, and staying there for prolonged periods of time. One season with extreme record-setting drought can be manageable, but ten seasons of "mere" moderate drought can be devastating.

It may well be that these Indus peoples did not have to diversify their crops. It may well be that they managed with what crops they had despite the drought - but they certainly didn't thrive, and likely began to slowly suffer the cumulative effects of the strain, in the same way a malnourished human can survive prolonged periods but becomes weak and more prone to sickness if exposed to it.

Suppose the drought never became catastrophic, but it remained a constant pressure on the region for generations. Grain prices rose, never quite going over the edge into calamity, but still straining the economy and society for decades without end. There was still enough food to go around, but little to no surplus. Consider how this would have affected politics in the region. In this age of humanity, you needed grain surpluses in order to do anything of substance.

Raising an army and going to war required you to have extra grain on hand to feed your troops, and to make up for the loss of agricultural labor caused by conscripting. Running a healthy economy, collecting taxes efficiently, and trading with your neighbors all required you to have extra grain, because most economic value existed in the form of goods rather than currency. Undertaking public works and maintaining infrastructure - from roads, to bridges, to water wells, to canals, to dockyards, to watchposts, to forts and castles, et cetera, et cetera - required you to have extra grain, because these are all the places you're going to start cutting costs first when times are lean and you're living hand to mouth. And certainly staying in power and not being overthrown by political rivals required you to have extra grain, because the moment someone else comes along who can promise people more than you can deliver, they start to wonder why they should remain loyal.

So suppose they existed in this semi-perilous situation for centuries, stopping somewhat short of plunging over the cliff. But things never really improved, even if they stopped getting worse, or even if they started to slowly get better at some point. And then before things could really start to truly improve, something major finally gave out and they at last careened over the edge and into sharp decline.

This is the importance of having a buffer. Yes, you can live hand to mouth - but it makes you much more susceptible to sudden unexpected shocks.