The uncertainty monster is out again

When I was reading the abstract of this new paper “Scientists unmask the climate uncertainty monster“, I was very glad I was sitting down. Even reading the summery was enough to let my head spin. If you sit down, here it is:

Increasing uncertainty in the climate system compels a greater urgency for climate change mitigation, according to new research. Scientists have shown that as uncertainty in the temperature increase expected with a doubling of carbon dioxide from pre-industrial levels rises, so do the economic damages of increased climate change. Greater uncertainty also increases the likelihood of exceeding ‘safe’ temperature limits and the probability of failing to reach mitigation targets. The authors highlight this with the case of future sea level, as larger uncertainty in sea level rise requires greater precautionary action to manage flood risk.

At word is Prof. Lewendowsky, a psychology professor of the University of Bristol, explaining why even more urgent action is needed.

My first reaction: wasn’t there that unequivocal evidence? Wasn’t there an ever increasing confidence in the science? Apparently according to Lewendowsky there wasn’t an advancing in science and we get to hear that there is … increasing … uncertainty!?!?! Oreskes, Doran, Anderegg, Cook and the IPCC made great effort in stating that there was a consensus because of this science that got clearer and clearer. And now there is Lewendowsky who states that there is even less certainty (but no worry, the conclusion is the same anyhow).

At first glance those statements didn’t make much sense. As far as I know, in reality the likelihood of exceeding safe temperature limits is not affected with how certain we are about it. Neither are the economic damages. It is not because we know something with much less certainty that something will be worse. Uncertainty are the unknown unknowns. The situation is what it is. Sure, it could well be that something will turn out to be much worse than we thought. But as far as we know it could turn out much better than thought. Or it could even turn out no problem at all. We just don’t know.

Such statements are not something new. Lewendowsky made them already in the past. For example in The Inescapable Implication of Uncertainty and Uncertainty is not your Friend. Those pages make somewhat more clear.

temperature rise probability distribution for a doubling of carbondioxide - Roe and Baker 2007 in science

Temperature rise probability distribution for a doubling of carbondioxide – Roe and Baker 2007 in Science

The issue is the long tail of the graph. The tail is long because it can’t be excluded that there are serious feedbacks in the climate system. The end of the tail goes to a difference of 6 degrees and more. Although it is only a small certainty, the possibility exists and this long tail could be catastrophic. I had seen this kind of reasoning before: it is a climate version of Pascals Wager. This makes it clear: as seen in the Pascal’s wager, when wanting to avoid this potential catastrophe, there is an increased sense of urgency.

Now back to reality. What was the evolution of this sensitivity over time? The graph that was discussed by Lewendowsky in 2012 was Roe and Baker (2007). But in the meanwhile the range changed: it increased, but it was towards the LOWER side.

Temperature rise probability distribution for a doubling of carbondioxide - Chris Hope (University of Cambridge)

Temperature rise probability distribution for a doubling of carbondioxide – Chris Hope (University of Cambridge)

Also, the standstill in temperatures tells us that carbon dioxide has less influence than was thought and/or there were other influences that were as strong as carbon dioxide. This points also to a lower sensitivity.

The problem with this is that the uncertainty is cutting both ways: sure, we could take into account the entirety of the probability distribution and prepare with more urgency for that 5% that is starting to get less likely. But there is also uncertainty about the solution. As seen in the Pascal’s wager, the assumption is that our action today will work and will have the desired outcome. Together with the possible catastrophic outcome acting would be a no-brainer. We assume that stabilizing or cutting CO2 emission will bring everything back to “how it was”. But in reality, will it work at all? The results of mitigation could as well be much worse than imagined. That is also part of the uncertainty.


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