Two strands of environmental philosophy run through the course of human history. The first holds that the natural state of the universe is one of infinite stability, with an unchanging earth anchoring the predictable revolutions of the sun, moon, and stars. Every scientific revolution that challenged this notion, from Copernicus’ heliocentricity to Hubble’s expanding universe, from Wegener’s continental drift to Heisenberg’s uncertainty and Lorenz’s macroscopic chaos, met with fierce resistance from religious, political, and even scientific hegemonies.

The second strand also sees stability as the natural state of the universe but holds that human beings destabilize it. The great floods...

As the last chapter’s sketch of the planet’s early climatic history shows, the greenhouse effect plays a critical role in the earth’s climate, and no sensible discussion of climate could proceed without grasping its nature.

The greenhouse effect has to do with radiation, which in this context refers to energy carried by electromagnetic waves, which include such phenomena as visible light, radio waves, and infrared radiation. All matter with a temperature above absolute zero emits radiation. The hotter the substance, the more radiation it emits and the shorter the average wavelength of that radiation. A fairly narrow range of wavelengths...

This basic climate physics is entirely uncontroversial among scientists.² And if one could change the concentration of a single greenhouse gas while holding the rest of the system (except its temperature) fixed, it would be fairly simple to calculate the corresponding change in surface temperature. For example, doubling the concentration of CO₂ would raise the average surface temperature by about 1.9°F, enough to detect but probably not enough to cause serious problems.

But, of course, it’s not actually that simple. Almost all of the uncertainty in climate science arises from the fact that, in reality, changing any single greenhouse gas...

How do we tell the difference between natural climate variations—both free and forced—and those that are forced by our own activities?

One way to tell the difference is to make use of the fact that the increase in greenhouse gases and sulfate aerosols dates back only to the industrial revolution of the nineteenth century: before that, the human influence is probably small. If we can estimate how climate changed before this time, we will have some idea of how the system varies naturally. Unfortunately, detailed measurements of climate did not themselves begin in earnest until the nineteenth century,...

Projections based on climate models suggest that the globe will continue to warm another 3–7°F over the next century. This is similar to the temperature change one could experience by moving, say, from Boston to Philadelphia. The warming of already hot regions—the tropics—is expected to be somewhat less than the global average warming, while the warming of cold regions like the arctic is projected to be more, a signal already discernible in global temperature measurements. Nighttime temperatures are increasing more rapidly than daytime temperatures, and the temperature over continents is increasing faster than that over the oceans....

Science proceeds by continually testing and discarding or refining hypotheses, a process greatly aided by the naturally skeptical disposition of scientists. We are, most of us, driven by a passion to understand nature, and that compels us to be dispassionate about pet ideas. Partisanship—whatever its source—is likely to be detected by our colleagues and hurt our credibility, the true stock of the trade. We share a faith—justified by experience—that at the end of the day, there are truths to be found, and those who cling, for emotional or ulterior reasons, to wrong ideas will be judged...

Global climate change presents us with unprecedented challenges. Since science can do no more than estimate a broad envelope of possible outcomes, from the benign to the catastrophic, society must treat the problem as one of risk assessment and management. At one extreme, we could elect to do nothing and gamble on a benign outcome. But if we are wrong we will saddle our grandchildren and their descendents with enormous problems. At the other, we could make serious economic and other tangible sacrifices that might prove unnecessary. Unfortunately, waiting much longer to see which way things go is not a...

Especially in the United States, the political debate about global climate change became polarized along the conservative-liberal axis some decades ago.

Although we take this for granted now, it is not obvious why the chips fell the way they did. The Republican Party has a respectable track record in protecting the environment, from Abraham Lincoln’s deeding of Yosemite Valley to California, to Richard Nixon’s establishment of the Environmental Protection Agency and signing of the Clean Air Act, to Ronald Reagan’s strong advocacy of the Montreal Protocol, which sought to protect the ozone layer, and George H. W. Bush’s support of...