Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgments
- PART ONE THE ASTRONOMICAL PLANET: EARTH'S PLACE IN THE COSMOS
- PART TWO THE MEASURABLE PLANET: TOOLS TO DISCERN THE HISTORY OF EARTH AND THE PLANETS
- PART THREE THE HISTORICAL PLANET: EARTH AND SOLAR SYSTEM THROUGH TIME
- PART FOUR THE ONCE AND FUTURE PLANET
- 21 Climate Change Over the Past 100,000 Years
- 22 Human-Induced Global Warming
- 23 Limited Resources: The Human Dilemma
- 24 Coda: The Once and Future Earth
- Index
- Plate section
22 - Human-Induced Global Warming
from PART FOUR - THE ONCE AND FUTURE PLANET
- Frontmatter
- Contents
- Preface
- Acknowledgments
- PART ONE THE ASTRONOMICAL PLANET: EARTH'S PLACE IN THE COSMOS
- PART TWO THE MEASURABLE PLANET: TOOLS TO DISCERN THE HISTORY OF EARTH AND THE PLANETS
- PART THREE THE HISTORICAL PLANET: EARTH AND SOLAR SYSTEM THROUGH TIME
- PART FOUR THE ONCE AND FUTURE PLANET
- 21 Climate Change Over the Past 100,000 Years
- 22 Human-Induced Global Warming
- 23 Limited Resources: The Human Dilemma
- 24 Coda: The Once and Future Earth
- Index
- Plate section
Summary
THE RECORDS OF CO2 ABUNDANCE AND GLOBAL TEMPERATURES IN MODERN TIMES
Ice cores contain trapped bubbles of air which, provided they can be properly dated, represent a record of the composition of air over time. Because of the weight of overlying layers of ice, compressing the pores in the ice, it is very difficult to extend the record back as far as that for temperature derived from the isotopic composition of the water itself. In fact, the manner in which the air bubbles were originally trapped in ice results in their movement upward or downward relative to the ice itself, making age determination a challenge.
Figure 22.1 displays CO2 values from an ice core collected in Greenland. The dating of the air was achieved by taking advantage of a byproduct of nuclear weapons testing: The isotope 14C reached a peak in Earth's atmosphere, from the detonation of nuclear bombs, in 1963. Using this peak in heavy carbon, geochemists M. Wahlen of Scripps Institution of Oceanography and colleagues determined that the trapped air was displaced by the equivalent of 200 years relative to the ice surrounding it.
With this important correction, the figure shows that, during the Little Ice Age, CO2 values were fairly constant. Beginning in the mid-1800s, carbon dioxide began to increase. Direct measurements from a station in Hawaii, selected to be high above any local industries and hence sampling worldwide CO2 borne by the trade winds, show that the increase accelerates after World War II.
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- EarthEvolution of a Habitable World, pp. 281 - 297Publisher: Cambridge University PressPrint publication year: 1998