Judith Curry: aanhangers menselijke broeikashypothese krabbelen terug

The issue of separating natural from anthropogenically forced variability, particularly in context of the attribution of 20th century climate change, has been a topic of several previous threads at Climate Etc. The issue of natural vs anthropogenically forced climate variability/change has been a key issue of contention between the climate establishment and skeptics. There are some encouraging signs that the climate establishment is maturing in their consideration of this issue.

Given that over the course of the next 10–30 years the magnitude of natural decadal variations may rival that of anthropogenically forced climate change on regional scales, it is envisioned that initialized decadal predictions will provide important information for climate-related management and adaptation decisions. Such predictions are presently one of the grand challenges for the climate community. This requires identifying those physical phenomena—and their model equivalents—that may provide additional predictability on decadal time scales, including an assessment of the physical processes through which anthropogenic forcing may interact with or project upon natural variability. Such a physical framework is necessary to provide a consistent assessment (and insight into potential improvement) of the decadal prediction experiments planned to be assessed as part of the IPCC’s Fifth Assessment Report.

The first sentence of the abstract really caught my attention: Given that over the course of the next 10–30 years the magnitude of natural decadal variations may rival that of anthropogenically forced climate change on regional scales. . . I don’t recall the climate establishment “giving” this one before. The implication of this is that the warming between 1970 or 1980 to 2000 should be operating under the same givens also.

The authors of this paper are members of the climate establishment, in terms of being involved with the WCRP CLIVAR Programme and also the IPCC. This paper arguably provides more fodder for skepticism of the AR4 conclusions than anything that I have seen from the climate establishment (the authors may not realize this). The issues surrounding natural internal decadal scale variability are a huge challenge for separating out natural from forced climate change. The same issues and challenges raised for future projections remain also for the warming in the last few decades of the 20th century. Sorting this out is the key challenge. No more unequivocals or very likelys in the AR5, please.