Unit 20


Unit Overview

This unit discusses the concept of climate change through various temporal lenses. The main sections are:

  • Evidence of climate change
  • The climatic history of the Earth
  • Mechanisms of climate change
  • The climatic future

Climate change is the long-term variability associated with the earth┬┐ocean┬┐climate system. The variability is caused by changes in certain boundary conditions, such as intensity of sunlight, arrangement of continents and oceans, and the composition of the atmosphere. Therefore, associated with the boundary conditions are the mechanisms of climate change. These mechanisms include solar output, Earth's orbit, continental drift, surface characteristics, and atmospheric particulates, and all those variables have been changing since Earth's beginnings. Consequently, Earth has experienced major changes in climate over the past hundreds, thousands, millions, and billions of years.

Evidence of climate change has been obtained from fossils, sediment cores, ice cores, tree rings, fossilized pollen, harvest records, and historical narratives. There is no reason to believe that changes in the Earth's climate should not happen in the future as well.

Unit Objectives

  • To examine various lines of evidence for climate change
  • To trace the history of climatic change on Earth, focusing on the past two million years
  • To discuss mechanisms that can cause climatic variations

Glossary of Key Terms

Glaciation A period of global cooling during which continental ice sheets and mountain glaciers expand.
Interglacial A period of warmer global temperatures between the most recent deglaciation and the onset of the next glaciation.
Teleconnections Relationships involving long-distance linkages between weather patterns that occur in widely separated parts of the world; El Nino is a classic example.

Unit Outline

  • Earth's environmental history
    • Formation of the atmosphere
    • Snowball Earth hypothesis
    • Cambrian explosion of life
    • Climate change
  • Evidence of climate change
    • Landforms and soils
    • Animal and plant fossils
    • Oceanic and lake sediment
    • Assembling the record of recent climatic variation
      • written records of direct observations
      • seafloor and ice sheet cores
      • tree rings
      • fossil pollen
      • glacial varves
  • Mechanisms of climate change
    • Challenging complexities
      • climate change analysis involves all five Earth spheres
      • focus on the interlinked atmosphere-ocean-ice-Earth system
    • External processes
      • variations in solar radiation
        • sunspots (short-term)
        • orbital cycles involving stretch, roll, and wobble (longer-term)
      • volcanism
      • uplifting and wearing away of land surface
      • plate tectonics (shifting distribution of landmasses and oceans)
      • greenhouse effect
    • Internal processes
      • circulation of heat and moisture by atmosphere
      • positive feedback effects
      • negative feedback effects
      • teleconnections
  • The climatic future
    • Speculation taking into account human interference

Review Questions

  1. Briefly describe the climate changes that have occurred from 1940 to the present.
  2. Chart the general climate trends for the past 1.5 million years, citing major episodes of glaciations and interglacials.
  3. Define the concepts of positive and negative feedback as they apply to internal processes of climate change, illustrating each with an example.