Chapter 23 - Lecture

Chapter 23: Global Ecology

Definition: ENSO is a large-scale atmospheric and oceanic phenomenon that influences ecological systems globally.
Impact:
- Warmer currents appear off Peru, typically during the Christmas season (El Niño relates to "Christ child").
- The Southern Oscillation refers to atmospheric pressure fluctuations across the Pacific Ocean.

Walker (1924): Identified a link between Pacific barometric pressure and monsoon rainfall, establishing the concept of the Southern Oscillation, which is linked to droughts in various regions.
Bjerknes's Contribution: Connected El Niño's temperature changes to atmospheric circulation, leading to storm formation over the eastern Pacific.

El Niño Phase:
- Characterized by warmer sea surface temperatures in the eastern tropical Pacific and lower pressure.
- Results in increased storms and precipitation in North and South America.
La Niña Phase:
- Cooler sea surface temperatures and higher pressure in the eastern Pacific, causing droughts in North America and increased rainfall elsewhere.

Under normal conditions, upwelling supports nutrient-rich waters along the South American coast.
During El Niño: Upwelling is reduced, compromising nutrient availability and leading to declines in fish populations.

Impact on the Great Salt Lake: The strong El Niño of 1982-83 resulted in high precipitation and significant ecological changes in the lake, demonstrating the interconnectedness of climate phenomena and ecosystems.
Effect on Australia:
- El Niño leads to droughts, while La Niña creates favorable conditions for plant establishment and diverse animal populations.
- Red kangaroos adapt breeding patterns based on rainfall, showcasing the influence of climate shifts on their life cycles.

Nitrogen Fixation: Human activities have increased nitrogen cycling significantly, with sources such as agriculture and industry contributing to 135-145 Tg/yr, which exceeds natural levels.

Tropical Deforestation:
- Critical for biodiversity; tropical forests contain half of Earth’s species. Brazil experiences the highest deforestation rates.
- Historical data shows a significant loss of forest area, adversely affecting global biodiversity and ecosystem health.

Loss of forest and the creation of edges expose fragments to harsher environmental conditions, impacting species diversity and survival.

Ice cores have revealed atmospheric CO2 records over the last 800,000 years, showing strong correlations between CO2 levels and global temperature patterns.

Fossil Fuel Impact: Burning fossil fuels contributes substantially to atmospheric CO2 levels, with several historical events disrupting the pattern of increases.
Ozone Layer Depletion: Discovery of significant ozone depletion led to international efforts, including the Montreal Protocol, showing human ability to manage atmospheric issues.