This is a carefully written hypothesis -- or three separate hypotheses -- to do with human impact on climate. The first two have the most space devoted to them. They assert that over the past 8,000 and 5,000 years respectively, the effect of humans in clearing forests for agriculture and irrigating lowlands for rice cultivation caused increases of carbon dioxide and methane which in turn kept global temperatures high enough to prevent the onset of the next glaciation. It's a good hypothesis and it feels indisputable. But I didn't read enough discussion about the complete cycles involved to totally convince me. He mentions it when discussing climate modelling very briefly: "the models attempt to simulate all of these interconnected responses [of carbon dioxide and methane concentrations in the atmosphere, temperature, ice volume, etc.] rather than analyzing them one-by-one in isolation". But for simplicity's sake he does here consistently analyze factors individually and in pairs, to make his argument. It's not a big flaw but it'd have been nice to see more discussion of how, for example, carbon dioxide, ice volume, and temperature relate to one another. But then you get into one hell of a confusing tangle of interconnected factors, so I can see why he didn't go there. Actually, not unlike the solubility of carbon dioxide in the oceans, which he admirably boils down to a single paragraph.

Anyway, those first two arguments about carbon dioxide and methane are good, and I wouldn't be surprised to see them form a central element in the future understanding of Pleistocene climate change. The last hypothesis is about pandemics causing the short-term drops in temperature over the past 2,000 years. Not so convincing. On balance I think his case is decent, but he had me cringing for half a dozen pages as he listed, in detail, European plagues, without mentioning the large numbers of people in India or China, or the mechanism by which population decline causes carbon dioxide concentrations to drop. Only at the end did he mention farm abandonment and reforestation as the mechanism, and that population densities in East Asia were high enough long enough ago that it didn't happen even with plagues. Fair enough. It's an interesting hypothesis but honestly the data presented here on both sides (two poorly matched ice core CO2 curves, and a cursory glance through the pandemic history of (mostly) Europe) are not good enough to convince me.

The last part is an interesting and brief glimpse at the industrial revolution's effects on climate that we are all probably sick of arguing about. It's interesting because it's the same stuff as usual but seen through a palaeoclimatologist's eyes, which is a much less gloomy perspective. The industrial CO2 pulse will go into the atmosphere, and then the ocean will soak it up. Life will go on. CO2 concentrations will return to their naturally, orbitally-forced decline, and a glaciation may or may not resume. The ice caps will not melt, due to their massive thermal inertia, although they may change a little around the edges. These are not predictions that rest on massive and much-argued-about general atmospheric circulation models, but simple consideration of all the causal relationships and response times. He does point out that by far the biggest casualties of our industrial CO2 emissions will be (1) the future cost of energy for humanity, once we've burned so much of our inherited carbon; and (2) the oceans. This last point he does not stress enough. The carbon we're burning in the form of coal and oil is going in the atmosphere, sure, and it will cause temperatures to spike, although we've already been doing that, as is the point of this book, for 8,000 years. But on a geological scale we're really pumping it into the oceans, which has the effect of acidifying them and irreversibly changing the ecosystems within them, if not (hopefully not) their thermodynamics.

His final point is a disclaimer for climate change denialists, and an odd but reasonable defense, wherein he says that the industrial CO2 input is bad, but not the worst thing we're doing to the Earth. Instead he lists: the destruction of ecosystems and ignorance of ecosystem services (e.g. forests), the depletion of fresh water, esp. groundwater, on a gigantic and irreversible scale, and the erosion and loss of lovely glacial sediments (topsoil) in prime agricultural land. Amen to those. ( )

Ruddiman, a palaeoclimatologist, hypothesizes that forest clearing, agriculture, rice production, and pandemics had begun to artificially change the climate as early as 8000 years ago, with the recent enormous effects of carbon use (oil, gas, and coal) building on the earlier changes. Ruddiman came to his conclusion when he noticed that the major forces in climate change normally caused by cycles in the earth's orbit (100,000 years), tilt (41,000 years) and precession, or wobble, (22,000 years), which had a clear pattern of increases and decreases of methane and CO2, began to veer off course starting about the time agriculture became common and humans began living in settlements. In addition, Ruddiman states that Earth should be in a glaciation of some sort at this part of the normal cycle and that global warming has delayed or, possibly, canceled it. A discussion with Ruddiman can be read at http://www.realclimate.org/index.php/arc.... The book is short (200 pages), very readable, and thought-provoking. ( )

First recommended to my by an anonymous man on a flight to Oakland, I bought this from Amazon and never regretted it. Filled with great and accessible information. ( )

An interesting read, if tedious in spots. William Ruddiman is a very well respected climatologist who advances his latest and somewhat controversial hypothesis in this book. It is generally accepted by scientists that since the dawn of the industrial era (about 200 years ago) human activity have been causing the Earth to be warmer than it would be otherwise. Dr. Ruddiman's hypothesis is that human impact on climate change extends back considerably farther: 8,000 to 10,000 years, to the dawn of agriculture on Earth. These effects are slight, but cumulative over the millennia and have, according to the author, actually prevented a scheduled ice age.

It's an interesting hypothesis, and Dr. Ruddiman certainly has lots of evidence to back it: climate records from glacial ice cores and lake-bottom sedimentary layers, computer models of climate change and information on very slight but significant eccentricities in Earth's orbit that effect overall climate and are responsible for cycles of glaciation. Unfortunately, I am no climate scientist and am in no position to evaluate his sources (this book was assigned reading for a Cultural Anthropology course as an example of a scientific approach to anthropology). Dr. Ruddiman does emphasize the fact that all this is very new and largely untested research; it may or may not hold up to future peer-review.

He also presents his data in a politically neutral way. The author does not say that global warming is either good or bad, but merely is. He does point out that the effect global warming will have on an individual depends largely on where they live and how much money they make. In the mid to high latitudes, global warming results in milder winters, longer summers and better growing seasons (good), but in the topical and sub-tropical latitudes it means either more monsoons or more drought, depending on where you live (bad, but the more money you make, the more you are able to mitigate these circumstances). He also mentions that given the modern, industrialized way of life with it’s dependence on fossil fuels and material consumption, it is unlikely that enough people the world over would be willing to make the sacrifices necessary to have a significant impact on global warming.

All in all an unorthodox hypothesis, interesting to learn, but certain sections (particularly the early chapters about Earth’s orbital variations and the effect it has on glacial patterns) are extremely dry and tough to get through, particularly if you don’t have a background in climatology. However, if what he says is true, it raises questions about current efforts to reduce our impact on the environment. What we tend to think of as "pre-impact" climate is actually not natural at all, but a result of pre-industrial humans efforts in agriculture. Is it then possible or even desirable that we reverse this course? After all, it was human-caused global warming that averted an ice age and allowed our species to thrive as has. On the other hand, we’re approaching average global temperatures that the Earth hasn’t seen for a billion years or more, and no one really knows what that means for life on the planet. ( )