Biology: How Life Works - Unit 4 Study Notes

Climate Patterns Over Geological Time

  • Earth’s temperature and CO₂ levels have fluctuated in cycles, transitioning between cold (glacial) and warm (interglacial) periods over 400,000 years.
  • The natural carbon cycle and ocean-atmosphere interactions previously stabilized Earth's climate without human influence.

Keeling Curve and CO₂ Trends

  • The Keeling Curve shows continuous CO₂ increase since 1958, revealing:
    • Seasonal fluctuations: CO₂ drops in warm months due to plant absorption and rises in cooler months from decay.
    • Long-term trend: Annual increase in CO₂ levels linked to human activities (fossil fuel combustion, deforestation).

Climate Change and Temperature

  • As CO₂ levels rise, so do mean surface temperatures.
  • Greenhouse gases cause temperature increases; natural climate models fail to explain recent warming without accounting for human emissions.

Oceanic Effects of CO₂

  • Rising CO₂ leads to two key oceanic consequences:
    • Increased ocean temperatures.
    • Decreased seawater pH (acidification) and lower oxygen storage capacity (deoxygenation).

Positive Climate Feedback Mechanisms

  • Soil Respiration: Higher temperatures increase soil microbial activity, releasing more CO₂.
  • Permafrost thawing releases CH₄ and CO₂, amplifying greenhouse effects.

Negative Climate Feedback Mechanisms

  • CO₂ fertilization may enhance plant growth leading to greater carbon sequestration.
  • Increased photosynthesis can stabilize atmospheric CO₂ levels, although crop nutrient quality may decline.

Nitrogen and Phosphorus Cycles

  • Nitrogen and phosphorus are limiting nutrients that control primary production and energy flow in ecosystems.
  • Human activities increase nitrogen availability, leading to:
    • Acid rain formation.
    • Eutrophication of water bodies.

Eutrophication and Dead Zones

  • Excess agricultural nutrients lead to algal blooms, depleting oxygen (dead zones) due to bacterial decomposition.
  • Aquatic life often cannot survive in these hypoxic environments.

Feedback Between Climate Change and Biogeochemical Cycles

  • Climate change directly impacts nutrient and carbon cycling.
    • Positive feedbacks can accelerate warming (e.g., permafrost melting).
    • Negative feedbacks can stabilize climate (e.g., carbon uptake by plants).
  • Eutrophication could represent both a positive and negative feedback mechanism depending on context.