David Peat

Re-envisioning the Planet 183tion, followed by a return as the ice melted. This ice age also providedthe opportunity for groups of Asian hunters to cross an ice bridge connectingthat continent to Alaska. From there they spread into theAmerican continent. (Other groups had probably colonized the Americaseven earlier.)There had been major ice ages before, during the Pleistocene era,just as there have been mini–ice ages in historical times. During one ofthe latter the Thames froze over to such an extent that Londoners wereable to hold winter fairs on the river. Likewise, as the sun’s output ofenergy changed, there have been periods of warming. We are now facedwith yet another such period of global warming that could well resultin major climatic disruptions. Again, this is the price we will have topay for all that progress and consumption during the twentieth century.A percentage of the sunlight that falls on the surface of the earth isreflected back into the depths of space. But naturally occurring gasesin the upper atmosphere, including carbon dioxide, methane, and nitrousoxide, trap this reflected heat and direct it back to earth again.The effect is like the panes of glass in a greenhouse that cause it to bewarmer inside than outside. Hence the term “the greenhouse effect.”Since the coming of industrialization and the widespread burningof fossil fuels—coal, oil, gasoline, and natural gas—the carbon dioxidecontent of the earth’s atmosphere has increased dramatically. The naturalconsequence is global warming. Some scientists predict a temperaturerise of 5°C over the next 50 years—taking us to the time whenthese same fuels will run out!Five degrees does not sound like that much. In general, it will meanwarmer winters and hotter summers. That doesn’t seem a high price topay, but the overall effect could be far more dramatic. To begin with,warming will not be uniform in each part of the globe; rather it willgive rise to a series of localized but major climatic disturbances. Whenone area suffers from drought another will experience highly increasedrainfall. Melting of the polar ice caps and mountain glaciers will releasean enormous amount of fresh water and result in a rise in thelevels of the world’s oceans, causing flooding of coastal areas and thepossible inundation of coastal cities. Also a combination of climatic