Chapter 23: Global Change

Global change: refers to all transformations or modifications of physical and biological components of Earth system over time



Types of global change: 

  • Gradual change 

  • Catastrophic 

  • Unidirectional 

  • Cyclic 



Gradual change:

  • Great Oxygenation Event (unidirectional change)

  • Archean → Paleozoci → Mesozoic → Cenozoic 

  • Plate tectonic processes take place over geologic time scales 

  • Supercontinent cycle



Catastrophic change:

  • Formation of Earth Moon system 

    • Collision of large protoplanet with Earth 

    • Ejects debris in space

    • Moon coalesced from the debris 

  • Advance and retreat of glaciers and ice sheets (cyclic)



Earth’s Climate Through Time

  • Climate oscillated between warm and cold conditions 

  • Several ice ages: unusual events occurring at irregular intervals 



Pleistocene Ice age: aka The Ice Age

  • Started with Pleistocene Epoch 

  • Ended with glacial retreat

  • Several ice sheets in northern hemisphere connected by sea ice 

  • Ice sheets flow from center, the point of maximum thickness, outward in all direction

    • Erosion dominates in the interior of ice sheets

    • Deposition dominates along margins


Traces of Pleistocene Ice Age:

  • Great Lakes and Finger Lakes

  • Glacial lakes

  • Submerged terminal moraine

  • Glacially polished landscape

    • Not covered by ice

    • Upper limit of ice cover

  • Till

  • Erratic boulders

  • Glacial striations


Consequences of Pleistocene Ice Age

  • Weight of ice causes lithosphere to bend downwards

    • Land surface subsides

  • Glacial rebound

    • Uplift

    • Rates of uplift depend on location (highest where ice sheet was thickest)

  • Changes in drainage patterns

  • Sea-level rise

    • Melting of ice-age glaciers

  • Colonization of the Americas

  • Climactic belts shifted towards equator

  • Vegetation belts shifted towards pole as glaciers retreated


Little Ice Age

  • Medieval warm period followed by Little Ice Age

  • Glaciers began retreating around 1850


Global T Change

  • T increased more than 1.2 Celcius by end of 2023


CO2 Concentration in Atmosphere

  • 50% increase


Assumption (NGS 2013)

  • All ice in our planet melts → sea level rises by 65 m