This book’s central thesis is that Classical Maya civilization collapsed as a result of a drought in Mesoamerica extending throughout the 9^th century AD. This particular drought was the local manifestation of Northern Hemisphere weather patterns that the author asserts have been repeated frequently over shorter time periods for thousands of years, even into this century, and which nearly always produce drought in Mesoamerica.

Once you accept Dr. Gill’s evidence for Mesoamerican droughts and their regularity, that evidence provides a parsimonious explanation for the end of Classical Maya civilization. After reading this book, I think many people will accept the evidence and the explanation.

There are, of course, more complex hypotheses, including overpopulation, warfare between Mayan city-states, external invasion, disease, over centralization, exhaustion of a stable environment, and peasant revolt. Mr. Gill argues that these are not needed to explain the collapse. This does not mean that such factors, if they existed, did not influence the course of the collapse, just that the collapse would have happened because of the drought whether or not other factors existed.

To support his thesis, which is clearly stated clearly at the beginning of the book, Dr. Gill takes the reader on a tour of a multitude of scientific disciplines. Each discipline studied adds information about the importance, frequency, possible causes and consequences of drought in Mesoamerican and on civilization and population trends throughout the world. Any one of these tours alone is worth the price of the book, since they are extremely well written and provide the foundation for further study on each topic covered.

In a chapter titled "Geology, Hydrology, and Water," the author describes the geology and hydrology of the Yucatan and the Maya highlands and the major drainage basins, and provides an extensive discussion of the water supply problem and how it was managed in the pre-Columbian period. The basic geology is the standard stuff: seasonal rainfall, permeable limestone, karstic drainage, deep underground fresh water usually inaccessible, except in the north through cenotes and along the east cost from freshwater lakes or lagoons. But, this chapter also explained how the Maya adapted to this environment. For example, the author describes natural surface depressions used as water reservoirs and known as aquadas. The Maya paved many of these small depressions and some were provided with chultunes, bell shaped chambers excavated below the aquada bottom to capture additional water when the aquada was filled. (A single chultun could hold 30,000 liters of water, enough to comfortably supply drinking and cooking water for twenty-five people for one year).

In fact, Mayan city-states and even smaller settlements were designed with water management a primary consideration, with central reservoirs, residential reservoirs, canals, and the terrain and pavement of the city itself all engineered to facilitate the collection and storage of water during the wet season. This was important, because, as explained in a chapter on "Paleoclimatology," small-scale (relative to the great final calamity) droughts were endemic to the Maya area as shown both by Maya water management strategies and more recent evidence from sediment recovered from the bottom of lakes. Records during the Spanish colonial period point to further famines on a regular basis after the conquest. In fact, during the colonial period, population looses from drought in the Yucatan ranged up to 30 or 40%.

In another chapter titled "Volcanoes and Weather" Dr. Gill argues that there is a strong correlation between the eruptions of large volcanoes around the world, and the worldwide weather patterns that lead to drought in Mesoamerica. This particular chapter not only provided evidence to support this correlation, but evidence that the volcanoes may have been a forcing mechanism for those weather patterns. Volcanoes and weather are a topic of some interest to me, and until I read this book, I had trouble finding a good introduction to the study of volcanoes, and to the relationship between volcanoes and weather. Now I have.

To save space and my own energy, I am not going to discuss the chapter on "Thermohaline Circulation." Except, I will say that that I learned enough in that one chapter on North Atlantic deep water formation and three dimensional ocean circulation models for all of the world’s oceans to help me understand an article on the subject recently published in the journal Nature. I will also skip lightly over the early chapter titled "Self-Organization" which discusses, among other things, the overall flow of energy in a civilization, and the important roll of exporting entropy to the environment by a civilization to reduce the potentially disruptive entropy in the civilization. I will also skip lightly over the chapter titled "Famine and the Individual" which describes how famine can rapidly lead to the complete collapse of social norms and the massive disruption of "normal" energy flows in any civilization.

Probably the most important or challenging single assertion Dr. Gill makes is changing the timing of the collapse of Chichen Itza. Traditionally dated around 1150 AD, and cited as an example of the ability of some Maya cities to survive the Classical collapse, the author re-dates this event to the 9^th century based partly on re-interpretation of inscribed calendar dates attributed to the period after the collapse. This particular assertion is probably one of the most controversial in the book and is critical to the author’s basic thesis. I suspect that it will be the focus of considerable argument. In support of this claim, the author provides a new interpretation of the relationship between Chichen Itza and the Toltecs, which itself is probably worth a fair amount of discussion.

I strongly recommend this book to just about anyone with an analytical mind. If you are interested in the general flow of Maya civilization this book has a lot to offer. If you are generally interested in the interplay between climate and civilization, this book also has a lot to offer. If you are just somewhat interested in topics such as global meteorology, volcanoes, tree-ring records in Europe and America, or the debate between uniformitariansm and neocatastrophism in the early study of geology, you will still find useful information that is readily accessible.