Is the Sun almost-intransitive?

Abstract

THERE is now ample instrumental, historical and proxy evidence for palaeoclimatic variability over time scales ranging from 10 to 10⁹ yr (ref 1). Although a great deal of research is still needed to establish more precisely the nature and finer spatial and temporal resolution of these changes, the main theoretical problem is to understand the mechanisms responsible for this variability over such a wide range of time scales. We suggest here that if the Sun were almost-intransitive, it could explain some of this climatic variability. Many hypotheses have been advanced by researchers in various disciplines based on physical processes, both terrestrial and extra-terrestrial^1–8 and although there is no general consensus as to the causes of variability over various time scales, the common view among climatologists is that the very long time-scale fluctuations with periods of ∼10⁸ yr can be explained by causes of terrestrial origin, such as the changes in oceanic and continental geometries^3,10. The intermediate time-scale fluctuations with periods of ∼10⁴–10⁵ yr are thought to have been caused by variations in Earth's orbital elements⁹. The relatively short time-scale fluctuations with periods of ∼10²–10⁴ yr are, on the other hand, hard to explain, because of the clear lack of a physical process with the appropriate time scale. Solar variability is, however, accepted as a serious contender^3,10. All these hypotheses, whether terrestrial or extra-terrestrial, have in common the assumption that the changes in climate are deterministic, that is, they are a causal response of the climatic system to a change in some environmental (internal or external) parameter, even though the actual mechanism of change is not usually understood.