9.3 Major climate events in Earth's history

Earth's climate has undergone dramatic shifts throughout its history. From glacial-interglacial cycles to mass extinctions, these events have shaped our planet's ecosystems and biodiversity. Understanding these past climate changes provides crucial context for our current climate crisis.

Causes of past climate events include changes in Earth's orbit, volcanic eruptions, and asteroid impacts. These led to consequences like sea level fluctuations, ocean acidification, and species extinctions. Evidence from ice cores, fossils, and geochemical proxies helps us piece together Earth's climate history.

Major Climate Events in Earth's History

Major climate events in Earth's history

Top images from around the web for Major climate events in Earth's history

• 

  Paleocene-Eocene Thermal Maximum - Wikipedia View original

  Is this image relevant?

• 

  Mass Extinctions | Biology for Majors II View original

  Is this image relevant?

• 

  16.1 Glacial Periods in Earth’s History | Physical Geology View original

  Is this image relevant?

• 

  Paleocene-Eocene Thermal Maximum - Wikipedia View original

  Is this image relevant?

• 

  Mass Extinctions | Biology for Majors II View original

  Is this image relevant?

1 of 3

Top images from around the web for Major climate events in Earth's history

• 

  Paleocene-Eocene Thermal Maximum - Wikipedia View original

  Is this image relevant?

• 

  Mass Extinctions | Biology for Majors II View original

  Is this image relevant?

• 

  16.1 Glacial Periods in Earth’s History | Physical Geology View original

  Is this image relevant?

• 

  Paleocene-Eocene Thermal Maximum - Wikipedia View original

  Is this image relevant?

• 

  Mass Extinctions | Biology for Majors II View original

  Is this image relevant?

1 of 3

• Glacial-interglacial cycles
  • Alternating periods of colder (glacial) and warmer (interglacial) global temperatures
  • Driven by changes in Earth's orbital parameters (Milankovitch cycles)
    • Eccentricity: variation in the shape of Earth's orbit around the sun (circular to elliptical)
    • Obliquity: changes in the tilt of Earth's axis (22.1° to 24.5°)
    • Precession: wobble of Earth's axis (rotation of the axis itself)
  • Examples: Last Glacial Maximum (~20,000 years ago), Holocene (current interglacial)
• Mass extinctions
  • Permian-Triassic extinction (252 million years ago)
    • 96% of marine species and 70% of terrestrial vertebrate species went extinct
    • Causes: Siberian Traps volcanic eruptions, methane release from seafloor clathrates, ocean acidification, and anoxia
  • Cretaceous-Paleogene extinction (66 million years ago)
    • 76% of all species, including non-avian dinosaurs, went extinct
    • Cause: Chicxulub asteroid impact (Mexico) and resulting climate change
• Paleocene-Eocene Thermal Maximum (PETM) (56 million years ago)
  • Rapid warming of 5-8°C over a few thousand years
  • Causes: massive release of carbon into the atmosphere from volcanic activity (North Atlantic Igneous Province) and destabilization of methane clathrates, leading to ocean acidification
  • Examples of effects: migration of tropical species to higher latitudes, ocean acidification, extinction of some deep-sea species

Causes and consequences of climate events

• Causes
  • Changes in Earth's orbital parameters (Milankovitch cycles) alter the amount and distribution of solar radiation reaching Earth's surface
  • Volcanic eruptions release greenhouse gases (CO2, CH4) and aerosols into the atmosphere
  • Methane release from seafloor sediments (clathrates) or permafrost due to warming or pressure changes
  • Asteroid impacts inject dust and aerosols into the atmosphere, blocking sunlight and causing cooling
  • Positive feedback loops amplify initial forcing (e.g., ice-albedo feedback, permafrost carbon feedback)
• Consequences
  • Shifts in global temperature and precipitation patterns affect the distribution of biomes (e.g., expansion or contraction of forests, deserts)
  • Sea level rise (during warm periods) or fall (during cold periods) due to changes in ice sheet volume and thermal expansion/contraction of seawater
  • Ocean acidification occurs when atmospheric CO2 dissolves in seawater, lowering pH and affecting marine organisms (e.g., coral reefs, shellfish)
  • Ocean anoxia (lack of oxygen) can occur due to warming, stratification, and increased microbial respiration, leading to mass extinctions
  • Habitat loss and species extinctions result from rapid changes in climate and ecosystem disruption
  • Ecosystem restructuring occurs as species migrate, adapt, or go extinct in response to changing conditions
  • Biogeochemical cycles (carbon, nitrogen, phosphorus) are altered by changes in temperature, precipitation, and ecosystem processes

Evidence for abrupt climate change

• Ice core records
  • Rapid changes in greenhouse gas concentrations (CO2 and CH4) are recorded in bubbles trapped in ice cores (e.g., Vostok, EPICA Dome C)
  • Abrupt shifts in temperature and precipitation are reflected in the isotopic composition of water molecules (δ18O, δD)
• Marine sediment cores
  • Shifts in ocean circulation patterns are recorded in the distribution of microfossils and geochemical tracers (e.g., δ13C, Nd isotopes)
  • Changes in ocean chemistry (carbon isotopes, oxygen levels) are preserved in the shells of foraminifera and other marine organisms
• Fossil records
  • Rapid turnover of species (originations and extinctions) is evident in the fossil record, particularly during mass extinction events
  • Migrations and extinctions of species can be traced through changes in fossil assemblages across time and space
• Geochemical proxies
  • Stable isotope ratios (oxygen, carbon) in fossils, sediments, and minerals provide information on past temperature, precipitation, and carbon cycle changes
  • Elemental concentrations (calcium, magnesium) in fossils and minerals can indicate changes in ocean chemistry and weathering rates

Past events vs current climate change

• The current rate of climate change is much faster than most past events, with the exception of some abrupt changes (e.g., PETM, Younger Dryas)
• The magnitude of warming projected for the coming centuries exceeds that of many past events, particularly when considering the rapid rate of change
• The primary cause of current climate change is human activities (fossil fuel burning, deforestation), rather than natural factors that drove past events
• The impacts of current climate change are occurring in the context of other human pressures on ecosystems (habitat fragmentation, overexploitation, pollution)
• The ability of species to migrate or adapt to current climate change may be limited by human-modified landscapes and the rapid rate of change
• The consequences of current climate change for human societies are significant, given our dependence on climate-sensitive resources (water, food, infrastructure) and the large populations living in vulnerable areas (coasts, drylands)