A new paper tells us that climate change is actually three times worse than we thought. For there may be tipping points, catastrophic changes, that cannot be worked back from and this shows that the carbon price should actually be three times higher than it is:

Climate policy aims to internalise the social cost of carbon by means of a carbon tax or a system of tradable permits such as the Emissions Trading System set up in the EU. But how do we determine the social cost of carbon? Do we take everything into account that should be taken into account? Most integrated assessment models (Nordhaus 2008, Stern 2007) calculate the net present value of estimated marginal damages to economic production from emitting one extra ton of carbon caused by burning fossil fuel.

However, global warming has many non-marginal effects on both the economy and on the carbon cycle. Climate catastrophes can occur that lead to sudden flooding, hurricanes, desertification, water shortages, etc. Many of such changes may be irreversible. Other catastrophes such as reversal of the Gulf Stream or sudden release of greenhouse gases from the permafrost lead to a sudden and long-lasting change in the system dynamics of the carbon cycle. Such changes in the system dynamics of the economy and/or the carbon cycle are called regime shifts. When such a shift takes place, this is called a tipping point. Scientists predict that at some point, structural changes will occur with effects that are very difficult or even impossible to reverse. The usual marginal cost-benefit analysis of existing integrated assessment models then puts us on the wrong track. The problem is much more serious than we think.

This argument seems, superficially, to have some legs. However, it doesn’t really hold up for their conclusion is:

If the potential tipping point is ignored, our calibration yields, in steady state, a social cost of carbon of $15 per ton of CO2, which is about the same as in well-known integrated assessment models. If the potential tipping point is not ignored, the social cost of carbon increases to $55 or $71 per ton of CO2, depending on whether we take a constant or an increasing marginal hazard rate as a function of the stock of atmospheric carbon. These are big potatoes, we would say. The precautionary returns are 0.6% per year and 0.5% per year, respectively. The need for precaution indeed decreases when emissions are reduced more with a higher tax on carbon.

Splitting the social cost of carbon into the three components provides additional insights. For example, the $71 per ton of CO2 is split into $6 for the marginal damages, $52 for the risk-averting component, and $14 for the raising-the-stakes component. The risk-averting component is by far the largest, and it is clear that ignoring potential tipping points is putting us on the wrong track when discussing climate policy to curb greenhouse gas emissions.

The problem here is that public policy is not based upon a carbon cost of $15. Rather, it’s based on the Stern Review result of $80. Which means that we’re already doing enough to cover the new findings of this paper.

In fact, we’re actually doing too much. The fuel duty escalator has led to us taxing petrol as if the correct carbon price is $160 a tonne CO2-e. The truth is we’re doing too much to avert or mitigate climate change even if (or perhaps especially if) we take all of the scientific consensus about the subject entirely seriously.