by Judith Curry
The thread on the recent Loehle and Scafetta paper (here and WUWT) have spawned the term “cyclomania” in the context of searches for natural cycles that can explain 20th century climate change and potentially predict climate change in the 21st century.
Cycles Research Institute
For those of you who are cyclomaniacs, you can indulge your mania at the Cycles Research Institute blog. The mission of the CRI:
“Our mission is to discover, understand, and explain the true nature and origin of cycles, thereby solving the mystery of recurrent rhythmic phenomena, as has been observed in both the natural and the social sciences, and while so doing, to instruct others, and to apply this new knowledge for the greater good of all life.”
The principals of the CRI include a physics professor, a professor of finance, market analysts, and Climate Etc. denizen Rog Tallbloke.
Some analyses of climate cycles
On timescales of decades to centuries, there have been several analyses of global climate cycles (on decadal and multidecadal time scales):
Loehle and Scafetta argue that previously observed cycles in solar motion and activity of 60 and 20 years, combined with an anthropogenic trend, can be used to model Earth temperature variations.
Actually, two and a half years ago I replicated the Global Surface Temperature record from about 1900 to present using only NINO3.4 SST anomalies, volcanic aerosol and sunspot data. My results also include the year-to-year wiggles. Do yours?
The graph is from the following post:
Here is another near perfect wiggle match (with accelerated response since 1995)
to coincide with sudden departure from natural event in 1995
but what does it mean?
Appinsys has an extensive post on 60 year cycles.
I also just spotted this new analysis by Clive Best.
I’m sure there are other similar analyses, these are ones that I have recently encountered. There are relatively few papers on this topic that have been published for global climate, but numerous papers have been published for regional climate. I would appreciate the citation of any articles that you are aware of on regional or global climate cycles on century time time scales.
Oscillations vs cycles
The favored period for cycles in these analyses seems to be 60, 20, and 9 years. A range of different mechanisms have been proposed (both forced and unforced).
In a chaotic system, one wouldn’t expect cycles but rather oscillations. Even regular external forcing is likely to result in an irregular and possibly lagged response. While variations in the sun, planetary orbits and magnetic fields may appear cyclic on some timescales, they are not cyclic on much longer timescales. For example, the Wikipedia has this to say on orbital variations:
Though the planets have been stable historically, and will be in the short term, their weak gravitational effects on one another can add up in unpredictable ways. For this reason (among others) the Solar System is chaotic, and even the most precise long-term models for the orbital motion of the Solar System are not valid over more than a few tens of millions of years.
Sunspots are cyclic, except for when they disappear for long periods such as during the Maunder minimum.
Oscillations such as the AMO and PDO are not cycles but irregular oscillations, with irregular periods. Assuming that the AMO and PDO are manifestations of natural internal variability of a chaotic system, the existence of these particular modes may come and go at any time.
In a complex chaotic system, there is no reason to expect that the forcings and response are easily separable from the decadal modes of natural internal variability. I think the approach of Tsonis in terms of diagnosing climate shifts in a chaotic system (synchronized spatiotemporal chaos) is generally the correct way to go in sorting this out.
The IPCC’s 20th century attribution problem
The IPCC’s attribution argument assumes that 20th century climate variability and change can be explained solely by external forcing (volcanoes, aerosol, greenhouse gases, solar). While the ambiguous word “most” in the IPCC’s attribution statement leaves room for unspecified natural internal variability and unknown forcing, their discussion of attribution makes clear their assumption of forced variations.
My judgment of the failure of the IPCC to make a convincing argument at the “very likely” confidence level was discussed in numerous previous posts, notably this post. Further, the only CMIP5 simulations that I’ve seen to date (NCAR) show results that don’t do a very good job of capturing either the magnitude of the trend or the decadal scale wiggles. So the possible explanations are:
- natural internal variability
- inadequacies in the forcing data for known agents
- unknown forcing agents
- model inadequacies