Mr. Flannery, a fascinating Renaissance man and scientist from "down under," offers a very compelling and readable treatise on climate change -- its history, science, and potential impacts. He begins by clarifying the simplest of confusions: Greenhouse gases (GHGs) are a class of gases that can trap heat at Earth's surface; Global Warming (GW) can result from the extra heat trapped as GHGs increase in the atmosphere; and Climate Change can result from GW placing pressure on Earth's climate system.

Historically, he describes how "for the past 10,000 years, Earth's thermostat has been set to an average surface temperature of ~57 F ... Earth's thermostat is a complex and delicate mechanism, at the heart of which lies CO2, a colorless and odorless gas. CO2 plays a critical role in maintaining the balance necessary to all life." Flannery delves into the history of climate change on our planet: "The great aerial ocean, indivislbe and omnipresent, has so regulated our planet's temperature that for 4 billion years, Earth has remained the sole known cradle of life amid an infinity of dead gases, rock, and dust ... Perhaps it is the means by which life perpetuates the conditions necessary for its existence ... The sun, like all stars, has become more intense as it has aged. Since life evolved, its rays have increased in intensity by 30%, yet the temperature of the surface of our planet has remained relatively constant. A drop of 0.1% in the solar radiation reaching the Earth can trigger an ice age; so Earth's long-term climate stability ... could not have resulted from mere chance."

The complexity of Earth's climate system is described in terms we can all understand. He identifies three principal cycles that drive Earth's climactic variability: "The longest ... concerns the planet's orbit around the sun ... an ellipse, whose shape changes on a 100,000-year cycle known as Earth's eccentricity [affects the intensity of the sun's rays throughout the year] ... The second cycle takes 42,000 years ... the tilt of the Earth on its axis [determines where radiation will fall]. This varies from 21.8 to 24.4 degrees ... The third and shortest cycle - every 22,000 years - concerns the wobble of the Earth on its axis [affects intensity of the seasons] ... Even at their most extreme ... the cycles bring an annual variation in the total amount of sunlight reaching Earth of less than 0.1%. Yet that seemingly trivial difference can cause Earth's temperature to rise or fall by a whopping 9F... It is certain that GHGs play a role."

Flannery discusses the science of prediction: "Among the most important and best supported of ... predictions are that the Poles will warm more rapidly than the rest of the earth; temperatures over land will rise more rapidly than the global average; there will be more rain; and extreme weather events will increase in both frequency and intensity." He delves into the results of complex models to paint a very clear picture of our not-too-distant future: "Scientists say that a 70% reduction in CO2 emissions from 1990 levels by the middle of the 21st century is required to stabilize earth's climate. This would result in an atmosphere with 450 ppm CO2, and our global climate stabilizing by around 2100 at a temperature of at least 2F higher than the present, with some regions warming as much as 9F ... Earth's average temperature is around 59F, and whether we allow it to rise by a single degree or 5F will decide the fate of hundreds of thousands of species, and most probably, billions of people. Never in the history of humanity has there been a cost-benefit analysis that demands greater scrutiny."

The main "tipping points" that scientists are aware of for earth's climate are explored by  Flannery: (1) a slowing or collapse of the Gulf Stream [cools Europe and becomes unstable in the long term]; (2) the demise of the Amazon rain forests [transpiration reduced, rain reduced, turns into desert]; and (3) the release of gas hydrates from the sea floor [releases colossal amounts of methane gas]. He describes how: "only a small change in temperature capable of turning soils from an absorber of CO2 to a large-scale emitter" (due to bacterial decomposition). He states that "we have known for some decades that the climate change we are creating for the 21st century was of a similar magnitude to that seen at the end of the last ice age, but that it was occurring 30 times faster. We have known that the Gulf Stream shut down on at least three occasions at the end of the last ice age, that sea levels rose at least 300 ft, that the earth's biosphere was profoundly reorganized, and we have known that agriculture was impossible before the Long Summer of 10,000 years ago."

Flannery points out that the politics, the pitfalls of current policies, and many potential solutions including energy efficiency, conservation, and renewable alternatives. He concludes on a positive but ominous note by identifying three possible outcomes: (1) Our response to limiting emissions is too slow or uncoordinated to avert great climate shifts, which destroy Earth's life support systems and destabilize our global civilization; (2) humanity acts promptly ... to reduce emissions, and so avoids serious climactic consequences; or (3) emissions are reduced sufficiently to avoid outright disaster, but serious damage to earth's ecosystems results. [However, over a long] period, the carbon cycle will need to be strictly controlled. Under this final scenario, humans would have no choice but to establish an Earth Commission for Thermostatic Control."

I highly recommend this book to those who wish to better understand the most dire threat to life on earth.