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Chapter 20: Problem 78

The carbon dioxide level in the atmosphere today is often compared with that in preindustrial days. Explain how scientists use tree rings and air trapped in polar ice to arrive at the comparison.

Short Answer

Expert verified
Scientists use tree rings (dendrochronology) and air trapped in ice cores to compare pre-industrial and current levels of CO2. Tree rings indicate the amount of CO2 in the atmosphere when the ring was formed, with thicker rings indicating higher CO2 levels. Ice cores preserve a snapshot of the atmosphere's composition over time, which scientists can analyze to measure past CO2 levels.

Step by step solution

01

Understanding Dendrochronology

Dendrochronology is the scientific method of dating tree rings to the exact year they were formed. This technique helps scientists estimate the amount of carbon dioxide in the atmosphere when the ring was formed. Each tree ring represents one year, and the thickness of the ring gives us information about how much the tree has grown in that year. Thicker rings typically indicate years with higher CO2 levels, as trees grow more when CO2 is plentiful.
02

Understanding Ice Core Sampling

Ice cores are cylinders of ice drilled out of an ice sheet or glacier. Air is trapped in the compacted snow and gets encased in the ice, preserving a record of the atmosphere's composition. Scientists can analyze those bubbles to determine the amount of CO2 in the atmosphere when that piece of ice formed. By looking at different layers of the ice core, we can get a snapshot of atmospheric composition going back hundreds of thousands of years.
03

Comparing Historical and Current Data

Using the data from tree rings and ice cores, scientists compare the levels of CO2 from preindustrial times to today. This comparison provides a clear picture of how human activity influences CO2 levels and contributes to climate change since the industrial revolution.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Understanding Dendrochronology
Dendrochronology is a scientific technique used to determine the age of tree growth rings, providing valuable insights into past climate conditions. Each ring on a tree's trunk signifies a year of growth, making trees excellent historical records of their environment.

Thicker rings suggest a year of abundant growth, often related to more favorable weather conditions and higher levels of carbon dioxide (CO2), which plants use during photosynthesis. Thus, by measuring and analyzing the widths of these rings, scientists can reconstruct past CO2 levels. This data is critical in establishing how atmospheric CO2 has fluctuated before industrialization and its natural variability.
Ice Core Sampling Explained
Ice core sampling involves drilling cylindrical ice samples from glaciers or ice sheets. These ice cores contain tiny air bubbles trapped during snow compaction over centuries. By studying the composition of gases enclosed in these bubbles, specifically CO2, scientists unlock secrets of the Earth's atmospheric history.

Each layer of ice corresponds to a different period, much like tree rings, allowing us to peer back into time. The deeper the ice core, the older the atmospheric snapshot. This method can date back hundreds of thousands of years, providing a direct and detailed measure of past CO2 levels and contributing to our understanding of the Earth's climate history.
Climate Change and Its Markers
Climate change is a complex and multifaceted issue that is marked by long-term changes in temperature, precipitation patterns, and other atmospheric conditions. One of the primary drivers of modern climate change is the increase of greenhouse gases, such as CO2, in the atmosphere.

  • Increased CO2 from burning fossil fuels
  • Rising global temperatures
  • Melting polar ice caps
  • More frequent and severe weather events

By analyzing historical data such as tree rings and ice cores, scientists can contextualize current climate trends against natural variability. As the historical CO2 levels were significantly lower than today's measurements, we can deduce that human activities have accelerated climate change.
Carbon Dioxide Comparison Over the Ages
The current atmospheric CO2 level is often contrasted with that of the preindustrial era to illustrate the impact of human activities. Dendrochronology and ice core sampling studies show that preindustrial CO2 levels were substantially lower, hanging around 280 parts per million (ppm), compared to today's levels that exceed 410 ppm.

These comparative studies are vital for understanding how drastically human activities, especially the burning of fossil fuels and deforestation, have altered the atmospheric concentration of CO2. The increase in CO2 is a significant factor driving current climate change because CO2 is a potent greenhouse gas responsible for global warming.
Historical Atmospheric Data and Its Relevance
Historical atmospheric data, obtained from natural recorders like ice cores and tree rings, serves as evidence of Earth's climatic past. It is the benchmark against which current data is compared, helping scientists understand the scale and pace of changes in atmospheric conditions.

By analyzing this historical data, scientists can distinguish natural climate patterns from those influenced by humans. The information is used for a variety of applications, including:
  • Validating climate models
  • Forecasting future climate scenarios
  • Influencing environmental policy and decision-making

This historical perspective is indispensable for assessing human impact and for the scientific community's ongoing efforts to model and predict climate change dynamics.

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Most popular questions from this chapter

How are past temperatures determined from ice cores obtained from the Artic or Antarctica? (Hint: Look up the stable isotopes of hydrogen and oxygen. How does energy required for vaporization depend on the masses of \(\mathrm{H}_{2} \mathrm{O}\) molecules containing different isotopes? How would you determine the age of an ice core?)

What effects do CFCs and their substitutes have on Earth's temperature?

The green color observed in aurora borealis is produced by the emission of a photon by an electronically excited oxygen atom at \(558 \mathrm{nm}\). Calculate the energy difference between the two levels involved in the emission process.

Jupiter's atmosphere consists mainly of hydrogen (90 percent) and helium (9 percent). How does this mixture of gases contrast with the composition of Earth's atmosphere? Why does the composition differ?

What is photochemical smog? List the factors that favor the formation of photochemical smog.
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