Something New Under the Sun: An Environmental History of the Twentieth-Century World.

• Author: Conniff, Ruth

Something New Under the Sun: An Environmental History of the Twentieth-Century World, by J.R. McNeill (Norton, 2000), is a sort of physics-for-poets explanation of the massive changes in our biosphere wrought by human beings over the last 100 years. McNeill is a historian, and he brings his humanistic perspective to bear on our current environmental predicament. If only we lived 700 or 7,000 years, instead of seventy, we would understand by simple firsthand experience the incredible effects we humans are having on our global life-support system, McNeill declares. Since we can't see it for ourselves, he does his best to describe it for us.

"The twentieth century ... may be an early stage in mass extinction," he writes. About 1 percent of the birds and mammals living in 1900 were extinct by 1995, putting us on the road to the sixth mass extinction in the Earth's history, the last one of which wiped out the dinosaurs. For the first time, however, the cause would be a single "rogue mammal"--homo sapiens. In one of many interesting and quirky asides, McNeill tells us that a particular person, Thomas Midgley, born in 1889 and the inventor of Freon and leaded gasoline, "had more impact on the atmosphere than any other single organism in Earth history." He compares the massive changes in land and water through catastrophic events like volcanoes and earthquakes, and he points out that recently humans have managed to have as grand an effect on the water and soil.

All in all, the news is not good, except from the point of view of certain select species we humans helped nurture--domestic plants and animals, rats, rabbits, cockroaches, crabgrass, and the viruses that cause the common cold.

McNeill compares us to cyanobacteria, which refashioned the world's atmosphere two billion years ago by excreting oxygen and increasing its presence in the air from one part per trillion to...