Catastrophes!: Earthquakes, Tsunamis, Tornadoes, and Other Earth-Shattering Disasters

10 Greenhouse Planet: Too Hot to Handle?

10 Greenhouse Planet Too Hot to Handle? [Carl] Sagan called [the earth] a pale blue dot and noted that everything that has ever happened in all of human history has happened on that tiny pixel. All the triumphs and tragedies. All the wars. All the famines. It is our only home. And that is what is at stake—to have a future as a civilization. I believe this is a moral issue. It is our time to rise again to secure our future. —Al Gore, An Inconvenient Truth, 2006 Cretaceous Park Imagine taking a time machine to the final half of the age of dinosaurs. Known as the Cretaceous Period, it spanned the interval of time from 145 million years ago until 65 million years ago, a total of 80 million years. This is 15 million years longer than the entire duration of the “age of mammals,” or Cenozoic era, which has lasted for the past 65 million years. If you stepped out of the time machine, you would not recognize much of the landscape and not just because dinosaurs ruled the world. The Rocky Mountains did not exist; most of California, Oregon, and Washington did not exist; and the Appalachians were not nearly so deeply eroded as they are today. The most notice- Greenhouse Planet 243 able difference would have been a huge shallow seaway filled with predatory marine reptiles, such as mosasaurs, plesiosaurs, ichthyosaurs, and sea turtles, as well as gigantic fish, with huge flying reptiles soaring overhead. Today, if you go to western Kansas or South Dakota, you find the ancient marine beds filled with these marine reptile fossils. The Western Interior Cretaceous Seaway (fig. 10.1) once extended all the way from the Arctic Ocean to the Gulf of Mexico, flooding the entire Great Plains and much of the future Rocky Mountain region, cutting North America in half. Although it was only a few hundred meters deep at its deepest, it was an impassable barrier for land animals. The dinosaurs of Montana, Alberta, or New Mexico, which lived on the western shore of this seaway, had more in common with the dinosaurs of Mongolia than with the dinosaurs of New Jersey because there was a temperate-forest land bridge over the Bering Strait to Asia. That would be the second striking fact about the Cretaceous world: instead of polar ice caps, the Arctic and Antarctic were temperate or even subtropical, with abundant trees, and a large fauna of dinosaurs, turtles, crocodiles, frogs, Fig. 10.1. Map showing the high sea levels of the Cretaceous that drowned the continents in many parts of the world and made it easier for dinosaurs from Montana to walk to Mongolia than to New Jersey. (Original drawing by Pat Linse) 244 Catastrophes! salamanders, and other animals living there. Many animals, such as crocodiles , cannot tolerate even the slightest freezing temperature, so they must have lived in relatively mild conditions even though above the Arctic and Antarctic circles the winters mean six months of darkness. For example, Cretaceous rocks on the North Slope of Alaska (below freezing most of the year today) yield abundant fossils of bald cypress, cycads, ginkgoes, ferns, and many other temperate and subtropical plants typically found in the swamps of Georgia or Florida today. Instead of the subfreezing annual temperatures, the summer temperatures in the region were about 10°C (50°F), or cool temperate. This is also true of the southern polar regions. Decades of work in southern Australia and even in Antarctica show the region inside the Antarctic Circle supported a varied fauna of dinosaurs, fish, turtles, flying pterosaurs, birds, amphibians , and even small mammals. The temperatures were similar to Alaska at the time, with lush, green vegetation. It included ferns, ginkgoes, cycads, podocarps (“yew pines”), numerous flowering plants, and Araucaria trees (known today as the Norfolk Island pine, or the monkey-puzzle tree). As in the Arctic, these plants could tolerate six months of darkness but not freezing, so they would have been dormant about half the year. Dinosaurs show an interesting mixture of ecologies. Most dinosaurs from Alaska are the same as the duckbill dinosaurs in southern Alberta, so it is reasonable to assume that they migrated from the region in herds during the winter darkness and returned in the summer (as most Arctic animals do today). Many dinosaurs from southern Australia, however, are small bodied and could not migrate. Their bones...