CA

Topic 9 and the Carbon Cycle

Introduction to Grand Cycles and the Anthropocene

  • Define grand cycles and their relevance to Earth's systems.

  • Introduce the term Anthropocene (the age of man), coined by Paul Crutzen around the turn of the millennium.

  • Highlight that geological ages typically span millions of years, while changes in the Earth’s system may occur over decades.

Importance of Understanding Grand Cycles

  • Emphasize the significance of understanding how materials, particularly carbon, cycle through the Earth's system.

  • Pose the key question: "Why do we care about the carbon cycle?"

  • Present data showing the rapid increase of carbon dioxide (CO₂) levels in the atmosphere due to human activities, occurring tens of thousands of times faster than geological changes.

  • Define goals:

    • Understand carbon dioxide movement within the Earth’s system.

    • Understand human impacts on greenhouse gas levels.

Overview of Carbon Cycle

  • Focus on:

    • Reservoirs of carbon: where carbon is stored (e.g., atmosphere, oceans, vegetation, soils).

    • Flows of carbon: how carbon moves between these reservoirs.

Key Components of the Carbon Cycle

  • Reservoirs include:

    • Atmosphere

    • Oceans

    • Plants and animals

    • Soil organic matter

    • Geological (rock) reservoirs

  • Flows include:

    • Photosynthesis: conversion of CO₂ into carbohydrates by plants.

    • Respiration and decomposition: release of carbon back into the atmosphere.

    • Exchange of CO₂ between oceans and atmosphere (both absorption and release).

    • Human activities (e.g., fossil fuel combustion, deforestation).

Human Impact on Carbon Cycle

  • Discuss how human activities alter the carbon cycle, particularly through:

    • Burning fossil fuels

    • Deforestation

    • Changes in land use and soil management

Carbon Cycle Before the Industrial Revolution

  • Reference the year 1750 as a benchmark for pre-industrial carbon levels:

    • Carbon in the atmosphere: 590 gigatons (GT)

    • Carbon in oceans: 38 GT

    • Carbon in plants and soils: 3,800 GT

    • Carbon in fossil fuels (geological reservoir): includes unknown buried quantities.

Post-Industrial Revolution Changes in Carbon Cycle

  • Since 1750, carbon levels have significantly increased:

    • Atmospheric carbon: increased to 794 GT (590 + 204 GT since industrialization).

    • Oceanic absorption: increased to 92.2 GT (70 GT + 22.2 GT since industrialization).

    • Additional human impacts such as land-use changes affecting carbon reservoirs.

Visualizing the Carbon Cycle

  • Emphasize the complexity of the carbon cycle with multiple reservoirs and the intricate flows among them.

  • Recognize the challenge in attributing observed changes in atmospheric carbon solely to fossil fuel use due to multiple interacting factors.

Detailed Examination of Flows in the Carbon Cycle

  • Discuss flows such as:

    • Photosynthesis: The process where plants convert atmospheric CO₂ and water into carbohydrates using sunlight:

    • Basic formula:
      (CO2 + H2O
      ightarrow ext{carbohydrates} + O_2)

    • Additional details on oceanic carbon uptake, biological carbon cycling, and human-induced changes in vegetation dynamics.

Seasonal Carbon Patterns Observed at Mauna Loa

  • Highlight the sawtooth pattern observed in CO₂ levels measured since 1958:

    • Winter peaks vs. summer troughs explained by seasonal vegetation activity (photosynthesis).

    • Increased amplitude in variations potentially linked to changes in vegetation cover and climate dynamics over the years.

Analytic Approaches to Understanding Carbon Dynamics

  • Introduce three analytic methods:

    1. Mass Balance: Identifying inflows and outflows of carbon to determine if reservoirs are increasing or decreasing.

    2. Residence Time: Calculating how long carbon remains in a reservoir before being cycled out.

    3. Response Time: Understanding how long it will take for the atmosphere to stabilize or return to pre-industrial levels after a change in input (e.g., cessation of fossil fuel burning).

Practical Examples and Calculations

  • Analyze the flows going into/out of the atmosphere in GT/year and their implications for atmospheric increase.

  • Show examples of calculating:

    • Estimated annual increase in atmospheric carbon (3 GT/year based on current inflows and outflows).

  • Discuss how residence time is derived from total reservoir content and flow rates:

    • Example Calculation: If approximately 750 GT exists in the atmosphere and flows in/out average out to 150 GT/year, residence time =\frac{750}{150} = 5 years.

Response Time Considerations

  • Elaborate on how changes in carbon inputs affect overall atmospheric carbon levels and the associated lag in atmospheric recovery.

  • Use the lake analogy to explain that the carbon removal process is dynamic, involving multiple pathways that extend the time before seeing stabilization.

Summary

  • Reinforce the complexity and interconnectedness of the carbon cycle, emphasizing the human influence on this critical global system.

  • Prepare for deeper discussions and calculations in future classes, especially as they relate to current and projected climate changes.