Paul M has a list of criticisms and flaws in the IPCC reports that I’d like to explore in greater detail.
Here is the first criticism:
A new form of calculus has been invented by the authors of the the IPCC’s Fourth Assessment Report (AR4), in order to create the false impression that global warming is accelerating…
Here is the graph:
Paul, do I have to point out that you are imputing motive here — you are stating the reason the authors included the graphic is to “create a false impression that global warming is accelerating.” In other words, you are asserting that they knowingly created a graph that misleads about the rate of global warming? I just want to make that clear.
The slope over the last 25 years is significantly greater than that of the last 50 years, which in turn is greater than the slope over 100 years. This ‘proves’ that global warming is accelerating. This grossly misleading calculation does not just appear in chapter 3 of WG1. It also appears in the Summary for Policymakers (SPM): “The linear warming trend over the last 50 years is nearly twice that for the last 100 years“. Thus, policymakers who just look at the numbers and don’t stop to think about the different timescales, will be misled into thinking that global warming is accelerating. Of course, we could equally well start near the left hand end of the graph and obtain the opposite conclusion! (Just in case this is not obvious, see herefor an example). A similar grossly misleading comparison appears at the very beginning of chapter 3, page 237: “The rate of warming over the last 50 years is almost double that over the last 100 years (0.13°C ± 0.03°C vs. 0.07°C ± 0.02°C per decade).“
Will someone more skilled in statistical analysis point out to me why this is grossly misleading and wrong?
Here is another comment:
It is the same story with the misleading comment in the SPM mentioned above (“The linear warming trend over the last 50 years is nearly twice that for the last 100 years“). This statement was not in the original version reviewed by the scientists. It was inserted into the final draft that was only commented on by Governments. The Chinese Government suggested deleting this, pointing out that ‘These two linear rates should not compare with each other because the time scales are not the same’. Well done to the Chinese Government for spotting that. Too bad their valid comment was ignored by the IPCC.
Interesting questions raised:
1. Is it wrong to say that the rate of increase in warming is greater in the last 50 years than over the entire period and why?
2. Why was the new graph included in the final draft?
3. Who was involved in the government review? I imagine governments had their own scientists reviewing it, not just politicos.
Paul — I have to ask — if the report included four different graphs, with each one focusing in on a specific time period, would you still complain about it? If there were four graphs showing 1860 – 2000, 1905 – 2000, 1960 – 2000, and 1980 – 2000?
What do you think the graph shows and what is the proper way of analyzing the graph?