geol 150 week 9 lecture 1

Overview of Ice Ages and Climate Change

• The climate has varied greatly throughout Earth's history, including periods much colder than today.

• Last Ice Age:

  • Occurred about 20,000 years ago, with large areas of North America covered by glaciers.

  • Ice thickness reached up to two miles in some regions.

• The average global temperature during the last ice age was approximately 4-5 degrees Celsius (7-9 degrees Fahrenheit) cooler than today.

• Concept of Ice Age Units (IAU):

  • One Ice Age Unit reflects significant climatic changes and can serve as a reference for understanding future climate scenarios.

Historical Climate Conditions

• The Earth has experienced various climates over its history:

  • Cretaceous Period:

    • Known as the "pothouse climate," sea levels were about 200 meters higher than today, and palm trees existed in regions now cold.

  • Snowball Earth:

    • An early Earth phase believed to be entirely covered in ice, with little to no geological evidence remaining.

Importance of Studying History

• Understanding Earth's climate history aids in predicting future climate conditions.

• History provides insights into patterns that help prevent repeating past mistakes, emphasizing learning from previous experiences.

  • Quote: "Those who ignore history are condemned to repeat its mistakes."

• Recognizing the unusual nature of current warming trends is crucial for assessing potential risks ahead.

Evidence of Ice Ages

• Geological Indicators:

  • U-shaped valleys, formed by glaciers, indicate past glacial presence as compared to V-shaped valleys typical in warmer climates.

  • Glacial Striations:

    • Marks left on rocks from glacier movement, providing evidence of the former extent and movement of these ice sheets.

  • Erratics:

    • Large boulders transported by glaciers, differing from the local geology and indicating glacial activity.

• Louis Agassiz:

  • Key figure in identifying ice ages through geological observations in the 19th century, despite initial resistance due to conflicts with established beliefs.

Understanding Glacier Mechanics

• Glacier Formation and Movement:

  • Glaciers are rivers of ice that erode land underneath, leaving behind distinctive landforms like moraines and kettle lakes.

  • Glacier movement occurs due to gravitational pull and melting at lower elevations, leading to an Equilibrium Line determining retreat and advance based on accumulation and loss rates.

Historical Mapping of Ice Ages

• At the last glacial maximum, significant ice coverage included the Laurentide Ice Sheet (North America) and Scandinavian Ice Sheet (Europe).

• The extent of these glaciers can be estimated by using geological records, radiocarbon dating of organic materials, and ocean sediment analysis.

Ocean Sediment and Ice Core Data

• Oxygen Isotope Analysis:

  • The ratio of O-18 to O-16 in marine sediments indicates historical ice volume and climate conditions.

• Ice Core Records:

  • Air bubbles trapped in ice provide valuable atmospheric composition data, revealing historical CO2 levels and other atmospheric conditions.

  • Dust particles trapped can inform on wind patterns and climatic phenomena.

Current Climate Insights

• Strong Correlation Between CO2 and Temperature:

  • Historical records show fluctuations in CO2 coincide with temperature changes, implying CO2 plays a significant role in climate systems.

• Recent observations indicate current CO2 levels are about 50% higher than historically recorded averages during ice ages, raising concerns about extreme climatic conditions.

Astronomical Influences on Climate

• Milankovitch Cycles:

  • Variations in Earth's orbit significantly affect climate over long time scales, initiating ice ages.

• Earth’s changing axial position impacts how solar energy is distributed, particularly affecting temperatures at high latitudes (e.g., 65 degrees north).

Conclusion

• Understanding the dynamics of past climates and ice ages is essential for predicting future climatic shifts and potential impacts on ecosystems and human societies.

• Studies combining geological history, oceanic data, and ice cores provide multiple lines of evidence supporting the existence and patterns of historical ice ages.