A really long time ago I wrote Ghosts of Climates Past. I’ve read a lot of papers on the ice ages and inter-glacials but never got to the point of being able to write anything coherent.
This post is my attempt to get myself back into gear – after a long time being too busy to write any articles.
The often-accepted hypothesis that the physical laws governing the behavior of an atmosphere determine a unique climate is examined critically. It is noted that there are some physical systems (transitive systems) whose statistics taken over inﬁnite time intervals are uniquely determined by the governing laws and the environmental conditions, and other systems (intransitive systems) where this is not the case.
There are also certain transitive systems (almost intransitive systems) whose statistics taken over very long but finite intervals differ considerably from one such interval to another. The possibility that long-term climatic changes may result from the almost-intransitivity of the atmosphere rather than from environmental changes is suggested.
The language might be obscure to many readers. But he makes it clear in the paper:
Here Lorenz describes transitive systems – that is, starting conditions do not determine the future state of the climate. Instead, the physics and the “outside influences” or forcings (such as the solar radiation incident on the planet) determine the future climate.
Here Lorenz introduces the well-known concept of “chaotic systems” where different initial conditions result in different long term results. (Note that there can be chaotic systems where different initial conditions produce different time-series results but the same statistical results over a period of time – so the term intransitive is a more restrictive term, see the paper for more details).
Well, interesting stuff from the eminent Lorenz.
A later paper, Kagan, Maslova & Sept (1994), commented on (perhaps inspired by) Lorenz’s 1968 paper and produced some interesting results from quite a simple model:
That is, a few coupled systems, working together can produce profound shifts in the Earth’s climate with periods like 80,000 years.
In case anyone thinks it’s just obscure foreign journals that comment approvingly on Lorenz’s work, the well-published climate skeptic James Hansen had this to say:
The variation of the global-mean annual-mean surface air temperature during the 100-year control run is shown in Figure 1. The global mean temperature at the end of the run is very similar to that at the beginning, but there is substantial unforced variability on all time scales that can be examined, that is, up to decadal time scales. Note that an unforced change in global temperature of about 0.4°C (0.3°C, if the curve is smoothed with a 5-year running mean) occurred in one 20-year period (years 50-70). The standard deviation about the 100-year mean is 0.11°C. This unforced variability of global temperature in the model is only slightly smaller than the observed variability of global surface air temperature in the past century, as discussed in section 5. The conclusion that unforced (and unpredictable) climate variability may account for a large portion of climate change has been stressed by many researchers; for example, Lorenz , Hasselmann  and Robock .
And here is their Figure 1, the control run, from that paper:
In later articles we will look at some of the theories of Milankovitch cycles. Confusingly, many different theories, mostly inconsistent with each other, all go by the same name.
Articles in the Series
Part One – An introduction
Part Three – Hays, Imbrie & Shackleton – how everyone got onto the Milankovitch theory
Part Four – Understanding Orbits, Seasons and Stuff – how the wobbles and movements of the earth’s orbit affect incoming solar radiation
Part Five – Obliquity & Precession Changes – and in a bit more detail
Part Six – “Hypotheses Abound” – lots of different theories that confusingly go by the same name
Part Seven – GCM I – early work with climate models to try and get “perennial snow cover” at high latitudes to start an ice age around 116,000 years ago
Part Seven and a Half – Mindmap – my mind map at that time, with many of the papers I have been reviewing and categorizing plus key extracts from those papers
Part Eight – GCM II – more recent work from the “noughties” – GCM results plus EMIC (earth models of intermediate complexity) again trying to produce perennial snow cover
Part Nine – GCM III – very recent work from 2012, a full GCM, with reduced spatial resolution and speeding up external forcings by a factors of 10, modeling the last 120 kyrs
Part Ten – GCM IV – very recent work from 2012, a high resolution GCM called CCSM4, producing glacial inception at 115 kyrs
Pop Quiz: End of An Ice Age – a chance for people to test their ideas about whether solar insolation is the factor that ended the last ice age
Eleven – End of the Last Ice age – latest data showing relationship between Southern Hemisphere temperatures, global temperatures and CO2
Twelve – GCM V – Ice Age Termination – very recent work from He et al 2013, using a high resolution GCM (CCSM3) to analyze the end of the last ice age and the complex link between Antarctic and Greenland
Thirteen – Terminator II – looking at the date of Termination II, the end of the penultimate ice age – and implications for the cause of Termination II
Climatic Determinism, Edward Lorenz (1968)
Discontinuous auto-oscillations of the ocean thermohaline circulation and internal variability of the climate system, Kagan, Maslova & Sept (1994)