In this sober warning, Mann (The New Climate War), director of the Center for Science, Sustainability and the Media at the University of Pennsylvania, examines epochal climate events of the past to underscore the current threat posed by global warming. The Earth, Mann explains, can self-regulate its...

In this sober warning, Mann (The New Climate War), director of the Center for Science, Sustainability and the Media at the University of Pennsylvania, examines epochal climate events of the past to underscore the current threat posed by global warming. The Earth, Mann explains, can self-regulate its temperature (as the sun brightened over billions of years, the greater heat caused more evaporation and rainfall on Earth, washing carbon dioxide from the atmosphere and keeping it cool), but doing so takes time; for example, 56 million years ago volcanoes released carbon into the atmosphere for 10,000 years at such high rates that the Earth’s temperature rose by 9˚F and remained elevated for 200,000 years afterward. Mann describes how 250 million years ago the Great Dying, which was caused by a spike in carbon dioxide levels from volcanic eruptions in Siberia, killed 96% of marine species despite playing out “about a hundred times more slowly than the current warming spike,” underscoring the urgency of the current crisis. The climate history edifies, though discussions of the physics involved in global warming can get a bit technical (“The Stefan–Boltzmann law of physics... tells us that all objects radiate energy in proportion to the fourth power of their temperature”). Still, this enlightens even as it unsettles. (Sept.)