Richard Tol's latest paper compares the estimated economic impact of climate change from the 2nd, 3rd, 4th and 5th assessment reports to show there is little statistical difference and compares this fact with the content of the technical summaries which appear to change over time.
Although the estimates may not change that much, the degree to which the IPCC is "certain" has increased over time (and justifies some additional rhetoric).
Everyone would agree I am sure that the IPCC should be objective and base their summaries on the scientific facts. Have they got better or worse in their "selling of the results"? Perhaps the more recent summaries are a better reflection of the facts?
The result that Tol finds is not surprising however. Climate change fatigue means that larger headlines are needed each time to get the same response from a beleaguered general public who are trying to cope with pressure on real incomes, employment opportunities, higher energy costs and rising house prices.
The real issue is what the IPCC and governments should do in light of these "not surprising" results? It should certainly not be taken as an excuse for non-action of climate change mitigation policies.
There is no doubt that the IPCC should stick to the scientific facts or it risks undermining its credibility. Leave the political spin to others.