A new book explores how global warming is linked to the worst mass extinctions in earth's history. In Under a Green Sky, paleontologist Peter Ward recounts how a sharp CO2 rise accelerated dramatic environmental changes in the past, and what that can tell us about our future. Rosanne Skirble reports.

Picture this: "Shorelines encrusted with rotting organic matter. From shore to horizon ? as far as the eye can see there is an unending purple color, a vast flat oily purple. We are under a pale green sky, and it has the smell of death and poison."

This is a scene from the book Under A Green Sky: Global Warming, the Mass Extinctions of the Past and What They Can Tell Us About Our Future.

The author, Peter Ward, has spent a career studying fossils. He specializes in catastrophic mass extinctions from the earth's ancient past ? what scientists call the 'Big Five.' "[Those] that killed off at least 50 percent of the species on earth, and one of them, the Permian, may have killed off 90 percent of the species on earth," he explains.

Ward, a University of Washington paleontologist, details the causes and consequences of these events in Under A Green Sky. He says most scientists embrace the idea that a giant asteroid hit the earth around 65 million years ago, hastening the demise of the dinosaurs. He describes the earth as it goes through a global blackout. "We have falling meteors coming back from the impact sites setting all the forests on fire. We have sulfur going into the atmosphere coming back as sulfuric acid, acidifying the ocean, acid rain in the lakes."

But asteroids do not explain the other mass extinctions. For that, Ward and others have found evidence in the fossil record that prolonged volcanic activity spewed huge amounts of carbon dioxide and other gases into the atmosphere. As he points out, "There was a short-term rapid increase in carbon dioxide. High C02 increases greenhouse temperatures on the planet."

Over thousands of years, that spike in CO2 and the resulting worldwide heat wave had nasty consequences. Winds ceased, ocean currents died and most marine life vanished from too much heat and too little oxygen.

Ward says things got even worse. "These warm anoxic oceans produced [surface] blooms of hydrogen sulfide-producing bacteria. Enough of that went into the atmosphere to kill land animals and land plants and cause the ozone to disappear as well."

Records show that environmental change began to accelerate when atmospheric CO2 hit 1,000 parts per million. Today's levels are one-third of that and rising.

Looking at the ancient evidence, Ward notes that ice caps began to shrink. "Melting all the ice caps causes a 75-meter increase in sea level. [That] will remove every coastal city on our planet." It will also cover earth's most productive farmland, the author warns, adding, "It will happen if we do not somehow control CO2 rise in the atmosphere."

Ward does see some positive signs in the fight against global warming. "Most people are now educated as to what it is and most everyone knows that it has to do with carbon dioxide and that we have to slow that down. There is half the battle right there."

Ward is also encouraged that people are beginning to make changes in their daily lives and demanding action from their leaders. He hopes his book helps readers put the current state of the earth into historical perspective. "[Recognizing] that we are on a planet that has violent convulsions, and that we humans are playing with nature in such a way that we could recreate what were some really awful times in earth's history, that we really tinker with the earth's atmosphere at our peril."

As Peter Ward writes in Under a Green Sky, "This moment on this Earth truly is a precious gift, to be savored and appreciated. If we needlessly destroy this world, it is unlikely we will find another to replace it."