In Depth Notes on Lectures 9-15

Lecture 9: Pleistocene Megafaunal Extinctions

• Arguments Supporting Human Role in Extinctions

• Many extinctions occurred ~10,000 BC coinciding with human migration to North America.

• Megafauna were not adapted to human presence, unlike in Africa where they developed survival instincts against humans.

• Advanced hunting technologies contributed to a rapid decline in megafaunal populations.

• Climate Change and Extinction

• Climate change alone is unlikely to explain the extinctions. Other factors include:

  • Human activity

  • Potential asteroid or comet impacts

• Around this time, global temperatures rose by 3 degrees, leading to biome shifts and ecosystem pressures.

• Ecosystem Imbalance from Species Removal

• Removing a single species can destabilize ecosystems (e.g., keystone species like Mammoths).

• Loss can cause a cascade of population declines among dependent species.

• Example: Alligators in the Everglades create water holes, crucial for other species' survival; their removal would endanger these species.

• Predator-Prey Dynamics and Extinctions

• Poor balance in predator-prey populations can lead to crashes.

• Over-predation can cause a decline in prey, leading to starvation among predators.

• Absence of predators can cause prey populations to explode, surpassing environmental carrying capacity, resulting in starvation.

• Comparison with Polynesian Extinctions

• Similar extinction patterns observed in Polynesia with human migrations.

• Burney’s Recipe for Disaster

• Extinction caused by a combination of factors:

  • Environmental stresses (climate change)

  • Increased hunting pressures due to reduced prey populations.

Lecture 10: Climate Events

• Medieval Warm Period & Little Ice Age

• Medieval Warm: 9th century A.D., conducive to agriculture in Europe (e.g., vineyards).

• Little Ice Age: 14th to 16th centuries, resulting in cooler temperatures, abandoned Viking settlements in Greenland.

• Evidence for Climatic Changes

  • Historical records, pollen data, and sea temperature analyses evidence the Medieval Warm Period and its subsequent cooling.

• Causes of Climatic Changes

  • Volcanic activity, reduced solar activity, increased productions of radioactive carbon-14 and beryllium-10.

• Cooling attributed to volcanic eruptions releasing sulfur which scatters solar radiation.

Lecture 11: Climate Models and IPCC

• IPCC Reports

• Provide scientific bases for climate policy.

• Address future warming scenarios and risks of climate change.

• IPCC Author Selection and Funding

• Scientists nominated by governments and NGOs; work is voluntary through institutions.

• Review and Approval Process

• Large groups of government officials and thousands of experts contribute to assure comprehensive scientific representation.

• Climate System Components
  Different components in models:

  • Atmospheric Component: simulates clouds, aerosols, and heat transport.

  • Land Surface Component: focuses on soil, vegetation, and water characteristics.

  • Ocean Component: simulates current movements and biogeochemical interactions.

  • Sea Ice Component: impacts solar radiation absorption and water exchanges.

• Forcings in Climate Models

• External factors, like greenhouse gas emissions and solar variability, impact energy absorption by the Earth.

Lecture 12: Nitrogen Cycle

• Nitrogen in Atmosphere

• Exists predominantly as N2 (78% of atmosphere).

• Natural Pathways for Nitrogen

• Nitrogen fixation (biological, human, lightning) re-enters atmosphere via denitrification.

• Reactive Nitrogen

• Forms like NH4, NO3, signaling its unstable state in the environment.

• Impacts of Reactive Nitrogen

• Eutrophication, air pollution, acid rain, and negative health impacts.

• N2O is a potent greenhouse gas impacting climate change.

Lecture 13: Ocean Acidification

• CO2 and Ocean pH

• Increased atmospheric CO2 leads to ocean acidification via carbonic acid production.

• Eutrophication and Coastal Waters

• Nutrient overload causes algal blooms, depleting oxygen, and intensifying acidification through decomposition.

• Impact on Marine Life

• Acidification affects shell-forming organisms (e.g., corals, pteropods), impacting marine ecosystems.

Lecture 14: Plastic Environmental Impact

• Plastic Production

• Crude oil and natural gas as primary materials.

• Greenhouse Gas Emissions

• Emissions during extraction, disposal, and incineration of plastics produce significant carbon emissions.

• Microplastics Distribution

• Found globally, including human tissues, affecting food chains and health.

• Degradation of Plastics

• Plastics release harmful additives and contribute to microbial disease spread, affecting aquatic ecosystems.

Summary of Key Points

Pleistocene Megafaunal Extinctions

• Human Impact: Extinctions around 10,000 BC coincide with human migration to North America; megafauna lacked survival adaptations.

• Climate Change Influence: Climate change was a factor, but human activity and potential asteroid impacts also contributed to extinctions.

• Ecosystem Disruption: The removal of keystone species destabilizes ecosystems, leading to population declines among dependent species.

• Predator-Prey Dynamics: Imbalance in predator-prey relationships can lead to either over-predation or prey population explosions, causing ecological collapse.

• Polynesian Comparison: Similar extinction patterns can be observed with human migrations in Polynesia.

• Causative Factors: Extinction driven by environmental stresses alongside increased hunting pressures due to reduced prey.

Climate Events

• Medieval Warm Period: Beneficial for agriculture in Europe; followed by the cooler Little Ice Age, which affected settlements like those in Greenland.

• Evidence of Climatic Changes: Derived from historical records and scientific data reflecting temperature variations.

• Climatic Change Causes: Influenced by volcanic activity and solar variations, particularly cooling from volcanic eruptions.

Climate Models and IPCC

• IPCC Reports: These provide a scientific foundation for climate policy regarding future climate risks.

• Model Components: Include atmospheric, land surface, ocean, and sea ice components which simulate various climate interactions.

• Climate Forcings: External elements affecting Earth’s energy balance, such as greenhouse gas emissions.

Nitrogen Cycle

• Atmospheric Nitrogen: Predominantly in N2 form; reactive forms lead to environmental issues like eutrophication and health risks.

Ocean Acidification

• Effects of CO2: Increased atmospheric CO2 results in ocean acidification.

• Impact on Marine Life: Negatively affects organisms that rely on calcium carbonate, like corals.

Plastic Environmental Impact

• Production and Emissions: Plastics produced from fossil fuels contribute extensively to greenhouse gas emissions.

• Microplastics: Ubiquity in ecosystems and potential harm to food chains and human health.

Arctic Amplification & Tipping Points

• Rapid Arctic Warming: Linked to global temperature rise due to loss of sea ice.

• Migration Challenges: Species face complexities when migrating to optimal conditions.

• Health Impacts: Climate change poses risks to vulnerable populations, exacerbating existing health issues.