Lessons from history's climate shifts

 To be more accurate, I should probably say that the paper is capable of being interpreted in all of those ways, rather than risk implying that the authors intended to do more than run the numbers and see what popped up. What they’re talking about is climate change in Europe, specifically between 1500 and 1800 AD – a period that encompasses the so-called Little Ice Age. It also encompasses a period that historian Eric Hobsbawm dubbed the General Crisis, when Europe was beset by a number of wars, inflation, migration and population decline.

The method employed by David Zhang from the University of Hong Kong and his colleagues was basically to look for a chain of causality in changes in things such as temperature, crop yield, migration, famine and war. On the one hand, their top-line conclusion, contained in the paper’s title, brooks little argument: “Climate change is the ultimate cause of large-scale human crisis.”

Breaking that down, the chain of causality flowed from temperature changes through alterations in biological productivity to the effects that might make up a “crisis” – war, famine, pestilence, migration and population loss. “We conclude that climate change was the ultimate cause of human crisis in preindustrial societies,” they write.

So let me work backward through the list of possible interpretations that I mentioned earlier. First, a statement of the obvious perhaps, because clearly in a preindustrial society if you have a drastic change in climate (such as rains not falling for several years) it’s going to have a dramatic impact.

Countries with the least developed infrastructures are in general more likely to be facing the biggest impacts. Yet the word “development” may also give a dollop of comfort here and there. And you can pick it up by looking at what’s happening in Australia now: The country is having to deal at the moment with a major drought, which could be here to stay – that bit’s not certain, but a major regime shift to hotter and drier conditions is eminently possible.

The future is all to play for, but in Australia we are seeing indications of how a society can adapt to climate impacts – provided it has the wealth and infrastructure to do so. One thing that I don’t think can be considered comforting – though others may disagree – is that this PNAS analysis looked at a crisis caused by cooling, whereas in the near future it’s warming to worry about. Zhang’s group notes that climatic shifts on the scale of a Little Ice Age would probably have had a small impact in North America because there was so much more land easily available for growing food.