by Judith Curry
Ergo, we should build down CO2 emissions, even regardless of what climate-models tell us. – Nassim Taleb
Nassim Taleb has posted an essay entitled Climate models and precautionary measures. Its short, reproduced in its entirety below (in italics), interspersed with my comments:
THE POLICY DEBATE with respect to anthropogenic climate-change typically revolves around the accuracy of models. Those who contend that models make accurate predictions argue for specific policies to stem the foreseen damaging effects; those who doubt their accuracy cite a lack of reliable evidence of harm to warrant policy action.
JC comment: Two recent essays of relevance here:
- Climate change denial, freedom of speech and global justice
- Richard Lindzen on the dueling editorials by Freeman Dyson and Kerry Emanuel
These two alternatives are not exhaustive. One can sidestep the “skepticism” of those who question existing climate-models, by framing risk in the most straightforward possible terms, at the global scale. That is, we should ask “what would the correct policy be if we had no reliable models?”
JC comment: The issue of ‘no reliable models’ was addressed in Driving in the Dark: Long-term strategies should be built not on “visions” of the future but instead on the premise that longer term predictions (that is, forecasts of situations years and decades out), however presently credible, will probably prove wrong. – Richard Danzig
We have only one planet. This fact radically constrains the kinds of risks that are appropriate to take at a large scale. Even a risk with a very low probability becomes unacceptable when it affects all of us – there is no reversing mistakes of that magnitude.
JC comment: This returns us to my previous essay on Taleb’s work Is climate change a ‘ruin’ problem? Excerpt:
In many ways, the risk of climate change is an aggregate of the risks faced by individual regions. The warming is not uniform over the globe, and with projected global warming, there are both ‘winners’ and ‘losers’ (see my Testimony). Another relevant question is whether a future ice age – occurring naturally – would be considered as ‘ruin’? The impacts of a future ice age are arguably more severe than doubling or even tripling CO2 (even if you believe IPCC projections). Not to mention that CO2 warming would delay a future ice age. I’m not really seeing AGW as a ‘ruin’ problem, i.e. a ‘catastrophe’. And finally the issue of ‘recovery’ is a time-scale issue (what is ‘forever’?) – e.g. the ice sheets in an ice age will eventually retreat. This whole issue of ‘ruin’ ties back to the issue of what actually constitutes ‘dangerous’ climate change. See these previous posts on the issue of ‘dangerous’:
Without any precise models, we can still reason that polluting or altering our environment significantly could put us in uncharted territory, with no statistical track- record and potentially large consequences. It is at the core of both scientific decision making and ancestral wisdom to take seriously absence of evidence when the consequences of an action can be large. And it is standard textbook decision theory that a policy should depend at least as much on uncertainty concerning the adverse consequences as it does on the known effects.
JC comment: The precautionary principle simply isn’t a good fit for a complex, wicked problem that isn’t a ‘ruin’ problem. From my post Permanent paradigm paralysis:
In their Wrong Trousers essay, Prins and Rayner argue that we have made the wrong cognitive choices in our attempts to define the problem of climate change, by relying on strategies that worked previously with ozone, sulphur emissions and nuclear bombs. While these issues may share some superficial similarities with the climate change problems, they are ‘tame’ problems (complicated, but with defined and achievable end-states), whereas climate change is ‘wicked’ (comprising open, complex and imperfectly understood systems). For wicked problems, effective policy requires profound integration of technical knowledge with understanding of social and natural systems. In a wicked problem, there is no end to causal chains in interacting open systems, and every wicked problem can be considered as a symptom of another problem; if we attempt to simplify the problem, we become risk becoming prisoners of our own assumptions.
Simply put, the current focus on CO2 emissions reductions risks having a massively expensive global solution that is more damaging to societies than the problem of climate change.
The precautionary principal is by no means the only decision analytic framework to use under conditions of deep uncertainty, see these previous posts:
- Can we make good decisions under ignorance?
- Decision strategies for uncertainty, complex situations
- Decision making under climate uncertainty
- Coping with deep climate uncertainty
- World Bank on Understanding Climate Uncertainty
- Alternative approach to assessing climate risk
Further, it has been shown that in any system fraught with opacity, harm is in the dose rather than in the nature of the offending substance: it increases nonlinearly to the quantities at stake. Everything fragile has such property. While some amount of pollution is inevitable, high quantities of any pollutant put us at a rapidly increasing risk of destabilizing the climate, a system that is integral to the biosphere. Ergo, we should build down CO2 emissions, even regardless of what climate-models tell us.
JC comment: CO2 is not a pollutant like black carbon aerosol and mercury. The direct effects of CO2 on humans and land ecosystems are not harmful; our understanding of possible harm from ‘ocean acidification’ is in its infancy. The alleged harm comes from model simulations under doubled CO2 concentrations of changes to regional temperature and precipitation, for which climate models are totally inadequate. So exactly what is a ‘harmful dose’ of global atmospheric CO2 remains an outstanding question.
Regarding Taleb’s statement: Ergo, we should build down CO2 emissions, even regardless of what climate-models tell us. See this previous post: Why the decision to tackle global warming isn’t simple.
This leads to the following asymmetry in climate policy. The scale of the effect must be demonstrated to be large enough to have impact. Once this is shown, and it has been, the burden of proof of absence of harm is on those who would deny it.
JC comment: I actually like this argument. Recall my reasoning about burden of proof in the paper Nullifying the Climate Null Hypothesis. The key point with respect to Taleb’s argument is that the scale of the effect has not been demonstrated to be harmful relative to the historical record of climate variability; allegations of harm are derived from simplified reasoning using climate models that are inadequate. So there are two issues here – the magnitude of the climate response to doubling CO2, and the societal and ecosystem impacts of this climate response. As per the IPCC WG2 report, any AGW impacts are very difficult to demonstrate, relative to natural climate variability, land use effects, population growth, etc.
It is the degree of opacity and uncertainty in a system, as well as asymmetry in effect, rather than specific model predictions, that should drive the precautionary measures. Push a complex system too far and it will not come back. The popular belief that uncertainty undermines the case for taking seriously the ’climate crisis’ that scientists tell us we face is the opposite of the truth. Properly understood, as driving the case for precaution, uncertainty radically underscores that case, and may even constitute it.
JC comment: Regarding the argument that uncertainty increases the cases for action, I have addressed the flaws in this argument several times:
Depending on your decision analytic framework and what you assume about ignorance and uncertainty, you can come to either conclusion: uncertainty increases the need to act, or uncertainty decreases the need to act.
The case for uncertainty increasing the need for action rests on a fat tail argument. See these previous posts for why I think the fat tail arguments regarding human caused climate change are not that useful:
- Worst case scenario versus fat tail
- Climate sensitivity: lopping off the fat tail
- Tall tales and fat tails
JC reflections
I really like Taleb’s writings on risk (e.g. black swans, anti-fragile, fooled by randomness). However, when he applies these ideas to complex issues such as climate change and GMOs, in my opinion his arguments fall way short.
Well, it was interesting going through all of my old posts that are relevant to the issues raised in Taleb’s essay. I provide the links here for newcomers (and old-timers who have forgotten them), but also for academics such as Taleb trying to apply ideas about risk to the climate change problem – which is not a ‘tame’ problem.
Filed under: climate models, Policy, Uncertainty