This book is a time capsule. I've seen it evolve into that over the past 30+ years. I first read it when it was published in 1979. At that time the subject of climate, ice ages, warm periods, and various theories of causation, could be discussed without the heavy dose of politics that are present today. And, make no mistake, whether you ascribe to the theory of human caused global warming or you do not....the adulteration of science and the tainting of it's objectivity caused by this matter have done irreparable harm.
Science must be independent of short term political expediencies.
I've reread this book at least a dozen times. It never strikes me as dated. Yes, there are no personal computers or cell phones and fools don't spend their entire waking lives playing video games as today. But, as the authors point out the "Boeings" still cruised at "42,000 feet" and 550mph. The world hasn't really changed that much in all this time. Climate models are still crunched through a Cray One Research Computer. That it was probably about as powerful as your pda ( or less ) is immaterial. Computers and what they did for science was then as prevalent as now.
The book is about the onset of the next ice age. Whether there will be another glacial period is not in question. As long as the Milankovitch cycles prevail, as long as the Sun's output is stable, and as long as there is significant land mass at high Northern Latitude there will be glacial epochs of approx. 100,000 years punctuated by interglacials of approx 12,000 years.
It should be mentioned that in the 70s the prevailing wisdom was that the start of the next glacial epoch was near. This is not politically popular today despite the fact that this interglacial is now at about the average age when prior warm periods ended.
Today, if anything else, the premise of this book is far more supportable and believable. Not from watching the evening news but from just some simple searching on the internet. Look up "Milankovitch Cycles" or "Vostok Ice Core Graph" when you have finished this little book.
Another interesting thing about this book is that it seems to me to be nearly identical to "The Day After Tomorrow" in many respects. In "Sixth Winter" the jet stream dips downward to bring incredible cold to the surface. In "The Day After Tomorrow" large cyclones pull stratospheric air to the surface with identical results.
One difference is that the authors of the "Sixth Winter" had no political position to support and no preexisting fan club to play to. The onset of the next ice is simply treated as something that will occur....without doubt....and probably in several thousand years. But, how it will begin and how fast it will progress is unknown. We know far more about the end of ice ages since the physical landforms survive to record the events. The beginnings are obscured by the commotion and chaos of the end. Thus, this book is a fictional account of how an ice might begin.
We already know that there will be another ice age....and soon.....if pesky facts like this interfere with your politics or prejudices, that is, if you have a closed mind filled to capacity with canonical truth about climate.....this book would be little else but heresy to you.