Third Assessment Report: 2003
“Most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”.
Fourth Assessment Report: 2007
“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.”
Fifth Assessment Report: 2012 (draft)
“Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use.”
It seems that the 95% confidence interval associated with the IPCC definition of “very likely” is now worth no more than a toss of the coin. How much have we been paying these people to produce “Well crafted figures and punchy take home messages“?
Still, look on the bright side, the overpaid and underclued IPCC numpties are starting to wander in the right direction.
Roger Pielke Sr also notes that the definition of climate change itself has changed:
It is interesting to note that the Inter-Governmental Panel on Climate Change (IPCC) (IPCC, 2012) has recently redefined climate change as
“A change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use”.
This is different from the previous definition. IPCC states
“This definition differs from that in the United Nations Framework Convention on Climate Change (UNFCCC), where climate change is defined as: “a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability.”
This is a sneaky move. In effect they are making a post hoc rationalisation to make their previous position more tenable, or a least less untenable…
Of course it remains to be seen whether the IPCC will put figures on the relative natural and anthropogenic contributions to climate change in the final version of the summary for policy makers.
Perhaps it’ll look a bit like one of the MET Office’s statements:
“We’re 40% certain at least 30% of the weather forecasts will be at least 30% correct.”