In the introduction, the derivation of the graph to replicate the claim that the costs of catastrophic global warming will be many times greater than mitigation policy costs was logically incomplete. This is a derivation of the two cost functions from a series of PowerPoint slides, which I find somewhat more satisfactory.

Slide 1

First draw two axis’s – for temperature and relative cost.

Slide 2

Next, add in five points.

A. If there had been no rise in human greenhouse gases, there would be no rise in temperatures and thus no consequential costly climate impacts.

B. With “business as usual”, there will be a huge amount of warming, with hugely costly consequential climate impacts.

C. Globally, policy could be used to stop any further rise in greenhouse gases, but with huge global cost.

D. No policy and no policy costs.

E. Intersection of two curves, which in Stern’s view is at the point of constraining warming to about 3 degrees above pre-twentieth century levels.

Slide 3

Connecting up the points AB (climate costs) and CD (Policy costs) with straight lines (linear functions), creates an intersection at point F.

To replicate Stern, we need cost functions that intersect at point E. That is the climate cost curve connects AEB and the policy costs curve connects CED.

Slide 4

Drawing curves within PowerPoint is beyond my current skills. Simple curves have symmetrical properties. The required cost curves do not have such properties.

Slide 5

Above is the actual graph used.

Slide 6

On my graphs the cost curves are unstable functions

For climate costs

RC = f(T⁴)

For policy costs

RC = f((10-T)⁵)

To justify policy

1. Must have reliable consequences of warming beyond human experience. Climate models must be robust for the high temperature rise forecast and have a phenomenal degree of precision on the shorter-term cost impact forecasts.
2. Must be sure that got achievable high-impact low-cost policies, with a highly results-driven approach to policy implementation.