Archive for September, 2010

Colouring Doubt’s Flag

2010-09-24

Judith Curry is keen to frame doubt in the form of an italian flag. Specifically with reference to this statement from IPCC WG1 Summary for Policy Makers:

Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.

Curry’s flag interpretation of this statement is that we could colour the flag 5% white (uncommitted belief), 67% green (anthropogenic forcing), 28% red (natural variability). A minor quibble: the opposite of “due to increase in anthropogenic GHG” is not “natural variability” as that excludes other anthropogenic activies such as sulphate emissions and secondary effects like ozone increases due to Montreal protocol. Anyway, her flag would look like this (if she drew it):

Does that seem right, can we be almost certain that there is only 5% wiggle room for doubt? Also, if I say that 70% of the variation is anthropogenic that doesn’t mean the rest (or almost all the rest) is natural, it just means I don’t know. I interpret the IPCC statement as meaning that there are a wide range of supportable beliefs about the anthropogenic cause of 20th century warming, but 95% (ish) of those will have more than 50% of the flag coloured green. Amongst the population of possible flags is this one:

Note that this flag already represents quite an extreme position with respect to the IPCC statement, because whilst it’s compatible with the IPCC statement, only 5% of the flags have a smaller green area than this. Here’s a more median position:

How can we represent the range of beliefs that are compatible with the IPCC statement. Like this?

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