Lecture 3

• daily cycle

  Earth's rotation
• seasonal


  Earth's orbit of the sun and axial tilt (obliquity)
• seasonal change

  • changing heat budget with latitude
  • change in daylight hours
  • change in weather patterns in terms of temperature and, indirectly precipitation, ice and snow melt
  • biosphere response in terms of vegetation growth and reproduction and in animal behavior (e.g. migration)
• sunspot cycle related to small variations in sun's output. low sunspots generally related to lower atmospheric temperatures
• earths orbit and axial tilt are key to controlling the warmth of northern hemisphere summers and the melting of winter snow
• croll-milankovitch cycles are the driver of glacial - interglacial oscillations
• Major climatic cycles over the past ~2.7 million years include glacial-interglacial cycles
• Effects of solar radiation variations associated with Milankovitch cycles are small compared with observed climatic changes
• The climatic system responds in complex ways, involving amplification (positive feedback) and damping (negative feedback) effects
• Factors involved in these effects include planetary albedo, greenhouse gases, and ice sheets
• The major variation over the past ~1 million years is a ~100,000-year cycle, with eccentricity having a smaller effect on solar radiation compared to obliquity or precession
• The 100,000 - year glacial-interglacial cyclicity only extends back to about 1 million years ago, before which the dominant cyclicity is around 40,000 years
• supercontinent cycle

  • climate
  • ocean currents
  • sea-level
  • mountain building (due to collisions)
  • environments
  • evolution
  • migration
• what determines the concentration of CO2 in the Earth's atmosphere?

  CO2 pumped into the atmosphere through terrestrial and submarine volcanism
• snowball earth:

  • Two low-latitude“snowball Earth”glaciations
  • 57 Ma and <16 Ma duration
  • Good evidence that CO2 outgassing by volcanic activity helped to end at least the Marinoan glaciation
• tsunami:

  • movement of water caused by an eruption, earthquake, terrestrial or submarine landslide
  • movement of whole column of water across oceans
  • potential catastrophic 1000s kms from the source
• Chicxulub crater, Mexico

  • association with the K-Pg mass extinction event
  • global layer of iridium-rich clays from the time (66Ma) indicating asteroid source
  • 300 Gt of sulphur (short-term cooling)
  • 425 Gt CO2 (long-term cooling)
  • 75% of all life extinct
  • possible link to Deccan flood basalts?
• 1918 flu pandemic (Jan 1918 – Dec 1920):involved H1N1 influenza virus, affected 500million worldwide, and killed 50-100 million
• The butterfly effect:

  • Simple systems of equations can result in non repeating behaviour that is very sensitive to initial conditions
  • Discovered by Edward Lorenz in1961 after looking at observations of a weather model
  • Gave rise to the scientific field of chaos theory
• Example of systems that exhibit deterministic chaos

  • Turbulence in fluid flows
  • Meteorology
  • Insect populations
  • geomorphological systems
  • hydrological systems
  • economic systems
• implications of deterministic chaos:

  • Complex patterns of change do not necessarily arise from complex causes
  • Complex effects can arise from simple non-linear relationships
  • Some natural systems maybe inherently‘unpredictable’:implications for predictions and forecasting
• Human-induced changes affect the lithosphere, hydrosphere, atmosphere, and biosphere
• Human-induced changes can occur more rapidly than natural background rates
• Land use change and disruption of river systems are examples of rapid human-induced changes
• Humans are now significantly more influential in moving sediment on Earth's surface compared to natural processes
• Direct human-induced changes can lead to significant indirect changes
• Examples include the increase in atmospheric CO2 concentration, global mean temperature rise, and sea level rise