Frozen Earth: The Once and Future Story of Ice Ages Read Online Free PDF Page A

determining temperature changes through time at any latitude on Earth; and an iconoclastic American schoolteacher-turned-academic who proved that parts of the northwestern United States had been ravaged by floods beyond imagining as ice age glaciers melted back into Canada.
    Louis Agassiz began discussing his ideas about an ice age at scientific gatherings in 1837, and within a few years, in 1840, he had published his observations and theory in a book.What was truly radical about his treatment was his proposal that ice had covered most of Europe during the ice age, even, perhaps, most of the land on Earth.As is often the case with new concepts, this one did not initially win many adherents.However, the debate about the reality of ice ages quickly became one of the most fiercely argued controversies of nineteenth-century science.It continued, unabated, for decades.

    And the eventual acceptance of the ice age theory was far from the end of the story.Since that time, literally hundreds, perhaps even thousands, of scientists have pursued research into the causes and effects of the ice ages, and many thousands of scientific papers have been written on the subject.In the course of that work, Agassiz’s contributions have been remembered in small ways and large.When researchers discovered evidence of a vast ice-dammed lake that had formed along the margins of the melting ice age glaciers in the central part of North America, they named it Lake Agassiz.In Winnipeg, Canada, which lies within the area that had been covered by the waters of glacial Lake Agassiz, there is even an Agassiz microbrewery.Agassiz, who complained when he came to the United States about the American practice of drinking iced tea with lunch instead of wine, undoubtedly would have been pleased.
    In principle, the idea of an ice age is a simple one—in the past, it was colder, glaciers were much more extensive than they are today, and huge ice sheets covered large sections of the continents that are now free of ice.However, understanding the phenomenon and determining how an ice age occurs, and what the ramifications are for the Earth and all its inhabitants, is far from simple.Today, it is difficult for anyone to be an expert in every aspect of ice age studies: the intellectual challenge presented by the geological evidence, with its multiple puzzles, has attracted the efforts of geologists, chemists, physicists, mathematicians, biologists, and climatologists.The work has taken on additional urgency in recent years because of mounting concern about the future of the Earth’s climate system.While at first thought this might seem odd—the dominant problem today is global warming, not cooling—it has become clear that our planet has experienced huge climate shifts during the current ice age (as we shall see, the Earth today is still in the grip of an ice age).Understanding how these changes in the global climate occurred in the past, and what their effects were, is a key step toward predicting future changes.But in spite of the great advances that have been made in working out the details of what actually happened during the ice age, there is still much uncertainty about how, andespecially why, an ice age actually begins.To be sure, there are hypotheses, but none have yet attained the status of an accepted scientific theory.Much remains to be done.
    Louis Agassiz built his ice age theory within the framework of the then-popular catastrophist view of Earth history: the idea that rapid, large-scale events were responsible for many geological observations.He didn’t really concern himself with a mechanism; he just assumed that temperatures had plummeted suddenly and the Earth “froze.”He envisioned glaciers extending as far south as the Mediterranean Sea in Europe, and deep into North America.However, later research has shown that Agassiz’s ice age was neither as rapid in onset as he proposed nor just a single cold period.We now know that the Earth’s most