I mentioned ‘tipping points’ the other day, in the context of the most recent claim about ‘consensus’ in ‘climate change’. I first came across them several years ago, and asked to see the papers that had investigated them, as well as the evidence on which they were based. The search didn’t get me very far. What I learned was that if you get into the paleo data, especially those which deal with the transition from glacial to inter-glacial states, it looks as though something happens to switch states. After all, before a certain point it was situation A, and after that point it is situation B. There must have been a moment, a point, where something occurred. What was it? The metaphor often used is an egg on a table: it may roll slowly towards the edge, but when it falls over, it ceases to be an egg. Humpty Dumpty and all the king’s men couldn’t put it back together again. But just before the egg fell, there it was, an egg with shell, white and yolk: two different states.
Some ingenious stories were assembled to show why such a tipping point might occur. The lack of convincing argument and evidence didn’t of course stop people talking as though tipping points really existed. James Hansen had no doubt at all. He said in 2008 that the tipping point had been passed when carbon dioxide levels had passed 350 parts per million (they were then about 385). And you hear the term quite a lot — most recently in the consensus paper already mentioned. There it was referred to as a certainty: ‘Earth is rapidly approaching a tipping point’. No conjecture there.
OK, what is the real situation now? As I read it, ‘tipping points’ have been reduced in credibility and status. Wikipedia says that a tipping point is ‘a somewhat ill-defined concept of a point when global climate changes from one ‘stable state to another’, and Wikipedia is no sceptic homeland in gobal warming. If you go to Wikipedia on ‘tipping points in climate change’ you are told that scientists in the field now rarely use the phrase ‘runaway climate change’. Barry Brook, a noted climate scientist in Adelaide, has (with others) recently published a paper in Trends in Ecology and Evolution that argues that at least in the ecological field global tipping points are unlikely, mostly because of the separation of continents. Tony Barnosky, an American scientist at UC Berkeley, disagrees. We humans connect the continents, he says. You can read the debate between them in an article in Scientific American.
At the heart of it is the lure of plausibility. We can find tipping points in all kinds of social and human affairs (‘the last straw…’). So why couldn’t we find one in climate? Well, we could, but so far, no one has succeeded, despite there being (allegedly) 40,000 papers on the subject. Have I read them all? No. Many if not most of them are behind paywalls. But make no mistake, if there was one that was indisputable, we would all know about it: the web brings forward every important paper, both from the orthodox point of view and from the dissenting, often within days of its publication.
One that I did read, and think is well argued, is a paper by Lenton, Held and others from 2008, which offers several possibilities for changes that would be irreversible, in the short run anyway: dieback of the boreal forests, the elimination of the Amazon rain forests, a disruption to the Indian monsoon, changes to the thermohaline circulation of the North Atlantic, and the warming of Arctic permafrost. The authors set out a formal way of defining tipping points and tipping elements. They make a good case for their process, but its relevance depends on the notion that warming is going on and is in some sense unstoppable.
Indeed, they almost say that the reason they wrote the paper is in response to that fear. ‘Many of the systems we consider do not yet have convincingly established tipping points. Nevertheless, increasing political demand to define and justify binding temperature targets, as well as wider societal interest in nonlinear climate changes, makes it timely to review potential tipping elements in the climate system under anthropogenic forcing.’
While the last IPCC report did go on at some length about tipping points, the draft 5th IPCC Report in various stages seems to suggest (if what I have read is accurate) that runaway climate change is no longer thought to be possible through anthropogenic activities. In short, the confidence of Hansen and others five years ago seems to have subsided, even if that mood has not reached the true alarmists.
What I did pick up from my reading, however, is that the Precautionary Principle is still alive and well in the orthodox camp. It is not a principle that I have much time for, in part because it reminds me too much of Pascal’s Wager, and partly because its origin is in the Rio Earth Summit of 1992, which was not in any way a gathering of the world’s best minds. Precautionists like to argue that despite our failure so far to show that climate tipping points exist, it is nonetheless prudent to behave as though they do. You might respond — at what cost? That whole debate must be for another post.
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Chief Hydrologist, a frequent poster on Climate Etc, pointed me to this mathematician’s paper on tipping points a while ago:
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