Kelsey et al have replied to Eric Wolff’s comment on their Climate of the Past Discussion Paper which I discussed yesterday. Wolff is concerned that the paper’s opening statement that “The existence of a ~1470 year cycle of abrupt climate change is well-established” does not reflect recent literature, citing multiple papers to make this point.
Kelsey’s response is “Please see references from highly ranked publications referenced in this article” followed by a list of papers (one of which, as Wolff points out in his subsequent reply, does not exist). This is not a response that indicates she is open to input from reviewers.
But what about these nutations which Kelsey et al think are, together with sunspots, driving the DO cycles. Nutations are wobbles in the Earth’s orbit caused by the gravitational pull of the Sun and the Moon on the Earth’s equatorial bulge. This wobble will cause a redistribution of insolation over the Earth, just like the obliquity and precession components of Milankovitch cycles. The key question is by how much? Is it enough, in conjunction with sunspots, to cause the DO cycles? The paper does not explore this critical question.
For reference, the obliquity cycle changes the angle at which the Earth’s angle tilts from 22.1° and 24.5°. The latitudinal component of the 18.6-year nutation is ±9.2″ (i.e. 9.2/60/60 = ±0.0025°). This causes the Tropic of Cancer (where the Sun is directly overhead at noon on the summer solstice) to move by a few hundred metres. It should be fairly obvious that insolation does not vary appreciably over such short distances. Nutation will also be linked to some changes in tidal amplitude, but it is really hard to imagine an 18.6-year cycle having much effect on millennial timescales.
I had expected A. M. Kelsey to be a retired engineer. Actually, she is a PhD student at the University of Queensland studying the palaeoecology and palaeoclimatology of Fraser Island in southern Queensland. Her coauthors are her supervisors – who I think are somewhat remiss for allowing her to submit this paper.
Why am I interested in this dubious paper? Three main reasons:
- If nutations and sunspots caused DO cycles then our climate is far more sensitive to forcings than anybody thinks it is.
- Climate change deniers will probably use it to argue our climate is only sensitive to sunspots and nutations and that greenhouse gas forcings are somehow insignificant.
- The open peer review process at Climate of the Past gives a window onto how peer review copes with “interesting” papers.