Willis Eschenbach has a posting on a recent paper on climate change damage impacts. This is my comment, with hyperlinks and tables.

My first reaction was “Oi– they have copied my idea!”

Well the damage function at least!

https://manicbeancounter.wordpress.com/2011/02/11/climate-change-policy-in-perspective-%E2%80%93-part-1-of-4/

Actually, this can be found by the claims of the Stern Review or AR4. Try looking at the table in AR4 of “Examples of impacts associated with global average temperature change” and you will get the idea.

A simpler, but more visual, perspective is gained from a slide produced for the launch of the Stern Review.

More seriously Willis, this is worse than you thought. The paper makes the claim that unlikely but high impact events should be considered. The argument is that the likelihood and impacts of potential catastrophes are both higher than previous thought. The paper then states

“Various tipping points can be envisaged (Lenton et al., 2008; Kriegler et al., 2009), which would lead to severe sudden damages. Furthermore, the consequent political or community responses could be even more serious.”

Both of these papers are available online at PNAS. The Lenton paper consisted of a group of academics specialising in catastrophic tipping points getting together for a retreat in Berlin. They concluded that these tipping points needed to include “political time horizons”, “ethical time horizons”, and where a “A significant number of people care about the fate of (a)

component”. That is, there is a host of non-scientific reasons for exaggerating the extent and the likelihood of potential events.

The Krieger paper says “We have elicited subjective probability intervals for the occurrence of such major changes under global warming from 43 scientists.” Is anybody willing to assess if the subjective probability intervals might deviate from objective probability intervals, and in which direction.

So the “Climate Change damage impacts” paper takes two embellished tipping points papers and adds “…the consequent political or community responses could be even more serious.”

There is something else you need to add into the probability equation. The paper assumes the central estimate of temperature rise from a doubling of CO2 levels is 2.8 degrees centigrade. This is only as a result of strong positive feedbacks. Many will have seen the recent discussions at Climateaudit and wattsupwiththat about the Spencer & Bracewell, Lindzen and Choi and Dessler papers. Even if Dessler is given the benefit of the doubt on this, the evidence for strong positive feedbacks is very weak indeed.

In conclusion, the most charitable view is that this paper takes an exaggerated view (both magnitude and likelihood) of a couple of papers with exaggerated views (both magnitude and likelihood), all subject to the occurrence of a temperature rise for which there is no robust empirical evidence.