The Two-Mile Time Machine

The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future

Richard B. Alley
Copyright Date: 2000
Edition: STU - Student edition
Pages: 240
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  • Book Info
    The Two-Mile Time Machine
    Book Description:

    Richard Alley, one of the world's leading climate researchers, tells the fascinating history of global climate changes as revealed by reading the annual rings of ice from cores drilled in Greenland. In the 1990s he and his colleagues made headlines with the discovery that the last ice age came to an abrupt end over a period of only three years. Here Alley offers the first popular account of the wildly fluctuating climate that characterized most of prehistory--long deep freezes alternating briefly with mild conditions--and explains that we humans have experienced an unusually temperate climate. But, he warns, our comfortable environment could come to an end in a matter of years.

    The Two-Mile Time Machinebegins with the story behind the extensive research in Greenland in the early 1990s, when scientists were beginning to discover ancient ice as an archive of critical information about the climate. Drilling down two miles into the ice, they found atmospheric chemicals and dust that enabled them to construct a record of such phenomena as wind patterns and precipitation over the past 110,000 years. The record suggests that "switches" as well as "dials" control the earth's climate, affecting, for example, hot ocean currents that today enable roses to grow in Europe farther north than polar bears grow in Canada. Throughout most of history, these currents switched on and off repeatedly (due partly to collapsing ice sheets), throwing much of the world from hot to icy and back again in as little as a few years.

    Alley explains the discovery process in terms the general reader can understand, while laying out the issues that require further study: What are the mechanisms that turn these dials and flip these switches? Is the earth due for another drastic change, one that will reconfigure coastlines or send certain regions into severe drought? Will global warming combine with natural variations in Earth's orbit to flip the North Atlantic switch again? Predicting the long-term climate is one of the greatest challenges facing scientists in the twenty-first century, and Alley tells us what we need to know in order to understand and perhaps overcome climate changes in the future.

    eISBN: 978-1-4008-3920-9
    Subjects: General Science

Table of Contents

  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-vi)
  3. List of Illustrations
    (pp. vii-viii)
      (pp. 3-10)

      We live with familiar weather—ski areas are snowy, deserts are parched, rain forests drip. But what if our climate jumped to something totally unexpected? What if you went to bed in slushy Chicago, but woke up with Atlanta’s mild weather? Or worse, what if your weather jumped back and forth between that of Chicago and Atlanta: a few years cold, a few years hot? Such crazy climates would not doom humanity, but they could pose the most momentous physical challenge we have ever faced, with widespread crop failures and social disruption.

      Large, rapid, and widespread climate changes were common...

      (pp. 11-14)

      To read the record of past climate shifts, we have to find the right history book. Humans hadn’t yet mastered writing the last time the climate jumped, so we can’t look up the answer in the library. Fortunately, there is a sort of “library” in ice sheets, lake beds, and the ocean floor that tells us much of what we wish to know.

      Archaeologists poke around in the trash dumps of ancient humans, looking for lifestyle clues. “Modern archaeologists” do the same in modern trash dumps, sorting out the Barbiedoll heads from the half-eaten hot dogs in our garbage to...

      (pp. 17-30)

      Drilling ice cores in Greenland or Antarctica usually involves getting on a ski-equipped plane and flying a few hundred miles over snow to a place where people live in tents at a temperature of thirty degrees below zero. Using an assortment of snowmobiles, skis, caterpillar tractors, computers, and a lot of “elbow grease” and “bigger hammers,” drillers race the short summer to pull sticks of ice up from the depths beneath their feet, analyze that ice, and ship it home. In the next few pages, we will take a quick look at the origins and practice of this odd pastime....

      (pp. 31-40)

      The ice of Greenland gives us incomparable records of past climates in and beyond Greenland. Tree-ring-like layers tell us how old the ice is. We can read how temperature and snowfall have changed in Greenland. Dust and sea salt in the ice were transported to Greenland by wind, and changes in their concentration in the ice tell us about changes in the winds that brought them. Bubbles of old air trapped in the ice contain information about past changes in the composition of the atmosphere itself. Recent layers are thick, allowing us to learn about individual seasons or even individual...

      (pp. 41-58)

      History is the story of what events occurred, and of when those events occurred. In this chapter, we will discuss how climate historians date ice cores and other sediments, and in the next chapters we will go on to see how to read the story of what happened.

      Many techniques have been developed for “dating” deposits, using changes in radioactivity or in chemical, physical, or biological characteristics that evolve at a known rate. The great number of dating techniques would form a book all their own, and we will not delve into them here. Suffice it to say that many...

    • 6 HOW COLD OF OLD?
      (pp. 59-70)

      Temperature dominates much discussion of climate. Humans live differently in hot summers than in cold winters, and differently in hot tropics than in cold polar regions. Our ancestors certainly noticed the cold of the ice age, and we spend much effort debating whether we will be affected by human-caused greenhouse warming.

      To study past climates and predict future ones, we wish to know temperatures in many places at many times. Patterns of temperature change will help reveal what caused climate shifts. For example, warming of most or all of the globe may result from an increase in greenhouse gases, but...

      (pp. 71-76)

      Whatever blows around in the air can land on an ice sheet and be buried in the snow. We can then analyze those materials and learn the history of things in the atmosphere.

      Aerosols—small particles in the air—have many sources. Dust blows from continents, and especially from the great deserts of the world. Dust from the Sahara falls on the Americas, and Chinese dust helps build soils in Hawaii. The details of the chemistry and minerals of dust can be used to learn where it came from. Such studies show that much of Antarctica’s dust blows in from...

      (pp. 77-80)

      Most glacier ice is bubbly. As snow turns to ice, much of the air between the ice grains is squeezed out, but some is trapped as bubbles. Ice is a great material for bottling old air—gas molecules don’t interact with the ice much, and gas molecules have a great deal of difficulty moving through the ice. The bubbles thus contain samples of old air, stacked up by age.

      Old air is a difficult thing to find except in ice cores. Some researchers have looked in antique fishing floats and the artwork of glassblowers, hoping to learn how the atmosphere...

      (pp. 83-90)

      By now, I hope that you are convinced that a dedicated team of drillers, pilots, cooks, scientists, and others can pull a two-mile-long piece of ice out of Greenland, cut up the ice, analyze it, and tell you how and when the climate changed in Greenland and in many other places. Our friends can analyze trees and mud from other regions, and tell you much about the past climates where the trees grew and the mud settled. The stories from these studies, and what they might mean, are the reason the government paid for us to go to Greenland, and...

      (pp. 91-98)

      Earth appears to have had a significant amount of ice for at least the last few million years, so we are away from the warm end of the full range of Earth climates. But the climate has been far from static over these few million cold years. Ice covers 10 percent of our land today, but covered 30 percent of our land only twenty thousand years ago. Walk across the U.S. Midwest or the plains of northern Europe and you’ll find the deposits left by vast ice sheets. These deposits are layers of mud and rocks that the glaciers picked...

      (pp. 99-108)

      We must now solve two riddles—why tiny changes in sunlight over 100,000 years have caused such huge changes in the world’s climate, and why sunlight on Canada, Europe, and Siberia is more important than sunlight on New Zealand Antarctica, or many other places. Neither riddle has been fully solved. It seems as though the ice sheets themselves are responsible for the size of the 100,000-year changes, primarily because the ice sheets take tens of thousands of years to grow but only thousands of years to die. And, somehow, it appears that the levels of carbon dioxide and other greenhouse...

      (pp. 109-128)

      We have now seen that Earth’s climate didn’t change too much over billions of years, and that ice-free and icy times have alternated over hundreds of millions of years, leaving us in an icy time during which glaciers have grown and shrunk over the last hundreds of thousands of years. The most important processes have been different over these different time scales—changes in the sun have been offset by changes in greenhouse gas consumption by rock weathering over billions of years, continental drift has altered patterns of atmospheric and oceanic circulation and of greenhouse gas production and removal over...

      (pp. 131-146)

      The Greenland ice cores and other records show that climate changes large enough and rapid enough to scare civilized peoples have occurred repeatedly in the past, and that our civilization has risen during an anomalously stable time. We would like to understand the climate jumps to learn whether they might happen again, and whether changes in human behavior can make climate jumps less likely.

      The jumps have occurred in Earth’s wildly complex, linked, feedback-dominated climate system in which atmosphere, oceans, ice, land surface, and living things interact with each other and with the solar system to drive weather forecasters and...

      (pp. 147-158)

      Conveyor belts in grocery stores usually work quite well, but occasionally one will fail. The great oceanic conveyor can also fail, tipping the world into new and unexpected climates.

      Suppose you wanted to stop a grocery conveyor. You could locate some of the store’s special, limited-time-only, free-with-$40-purchase flatware, grab a fork, and try to jam it into the mechanism. A good plan is to stick the fork into the gap where the conveyor belt goes down. The conveyor will try to pull the fork down but get it stuck, which may cause the conveyor to bind up and stop.


      (pp. 159-166)

      Why must the climate keep jumping among rows and levels, rather than settling down to watch the concert? We have a good story for the Heinrich events, with changes in ice sheets causing sudden delivery of fresh water to the north Atlantic and stopping the conveyor. For other events, however, we really don’t know. Volcanoes, the sun, floods, and other causes have been suggested. Some of these can now be eliminated—it probably wasn’t the volcanoes—and others may be part of the answer—the floods matter.

      A large volcanic eruption puts enough sulfuric acid into the stratosphere to block...

    • 16 FUELISH
      (pp. 169-180)

      Ice cores and other sediments show that large, rapid, and widespread climate changes have been common on Earth for most of the time for which we have good records, but have been absent during the critical few millennia during which agriculture and industry arose. At least some of those large changes appear to have been triggered by increased freshwater delivery to the north Atlantic. Climate jumps have been especially common when changes were occurring in important parts of the climate system, including summer sunshine in the north, carbon dioxide in the atmosphere, and ice-sheet size.

      The critical questions for us...

    • 17 DOWN THE ROAD
      (pp. 181-184)

      What are the odds that natural or human activities will trigger an abrupt climate change big enough, fast enough, and soon enough to matter in economic discussions? The simple answer, again, is that we do not know. The widespread realization that such an event is even possible is only a few years old. We continue to suspect that the known north Atlantic “light switch” is only one of several such switches in the climate system, but we aren’t even sure about this. Much knowledge is needed before we can begin to predict the known light switch, and it remains possible,...

      (pp. 185-192)

      By now, we have extracted a lot of information from the Greenland ice cores and many other sources. I hope you are convinced that the climate has changed in the past—greatly, rapidly, and across much of Earth. Such changes could happen again, and cause grave problems for humans. Humans ourselves might trigger such changes. What should we do about this?

      The simple answer is that I don’t know. As a scientist, I am one of those lucky people who are paid to go to fascinating places with wonderful people and learn new things. We hope that the things we...

    (pp. 201-222)
    (pp. 223-224)
  12. INDEX
    (pp. 225-229)