Deutsche Bank tries to answer the sceptics by attempting to demonstrate the the AGW is not completely refuted.

The sceptics arguments do indeed fail to amount to a complete refutation of the AGW case. Most of the “sceptic” arguments are against the idea that there has been no anthropogenic warming at all and that there is no evidence at all for the case. This would be hard to establish, and most “sceptic” scientists would never make this case. But almost equally hard to establish is the case that there will be extreme warming in the future, with likely catestrophic and irreversible consequences. At the very least there must be a clear demonstration that the likely economic impact (valuing the flaura and fauna as well), will be greater than the economic impact on human society of reducing CO2 emissions. Being able to demonstrate that the extreme opposite is implausible (in the vaguest terms) does not establish a position without unambiguous evidence and relying on unstated assumptions. There are some analogies that might highlight my perspective.
1. In medicine to have a reasonable expectation that the “treatment” will leave the patient better off than the cure. Simply showing that a few patients survived the treatment and recovered from the illness does not mean that the treatment worked. Nor does showing that some patients suffered adverse (non-fatal, but painful) side effects from a generally successful treatment to a condition that is 100% fatal without this treatment mean, that the treatment should not be used.

2. In considering a loan to finance a new business venture, the lending bank would want to see more in the plan tham that revenues will be generated. It would want to see a reasonable expectation that even with some set-backs, it could both deliver an income to the borrowers and sufficient surplus to repay the loan.
3. In a criminal case, if all the prosecution had to do was
   (a) present a case, that could not be challanged by the defence no matter how weak.
   (b) demonstrate that the defence had not proved their case beyond reasonable doubt, whilst being able to dismiss any evidence they presented on the flimsiest of evidence, including that defence counsel are paid to be biased.

4. A child caught smoking behind the bike-sheds is told that they have shortened their life by up to a decade. This will happen on average if they smoke heavily throughout their adult lives, but will not happen, on average, if it is ten cigarettes a week for five teenage years. They may have minor health issues, such as less ability to fight off the common cold.

What they have missing here is the huge middle ground – not of some truth on either side – but the middle ground where there is a an insufficient case established and / or, an insuffiently coherant plan, and demonstrated capability to carry out the plan, to gain a signficantly positive outcome. That is to give a reasonable expectation that the solution will leave the planet and the human race the better off for having acted.

Put another way, without a clear-cut case that an imminent, catestrophic disaster can be averted with a clear-cut plan, that has little adverse consequences, then there is ground to be made in actively trying to clarifying the extent of our collective scientific knowledge and the improving on the solutions.

Hatip BishopHill