Paleoclimates: Climate change and Biodiversity

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Paleoclimates Climate change and Biodiversity

• Ryan van der Marel
• 26 September 2007
• ENVI 5048

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Agenda

• Broecker, W. 2000. Abrupt climate change causal
  constraints provided by the paleoclimate record.
  Earth-Science Reviews. 51 137-154.
• Foley, J., M. Coe, M. Scheffer and G. Wang. 2003.
  Regime shifts in the Sahara and Sahel
  interactions between ecological and climatic
  systems in Northern Africa. Ecosystems. 6
  524-539.
• Discussion.

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The two-mile time machine

• GRIP, GISP II, Vostok
• d18O (oxygen isotope record)
• µA (ECM Electrical conductivity record)
• Benthic foraminifera (forams)

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Climate cyclicities

• Milankovitch cycles (100/40/20 kyr)
• Orbital forcings
• Heinrich events (100 kyr)
• Ice-rafted debris
• Dansgaard-Oeschger oscillations (1.5 kyr)
• Younger Dryas
• Medieval warm-Little ice age oscillation
• Antiphasing in Antarctica

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Glacial/inter- climate record
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Climate forcing

• North Atlantic Deep Water circulation

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The case for rapid climate change

• Thresholds and tipping points
• Paleoclimatic evidence of abrupt reorganizations
• Bi-polar seesaw

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Implications for biodiversity

• . . . for when forced by increasing greenhouse
  gas inventories, the thermohaline circulation in
  most existing joint ocean-atmosphere models
  slows
• (Manabe and Stouffer, 1993 Weaver and Hughes,
  1994
• Stocker and Schmittner, 1997 in Broecker, 2000
  138).

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Outstanding questions

• How much?
• How fast?
• When?

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Case study Foley et al, 2003

• Strong evidence of regime shifts in Sahara and
  Sahel regions.

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The African Humid Period
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Explanations

• Slow, steady changes stochastic trigger
  regime shift
• Insolation GCM positive feedbacks
  vegetative and non-vegetative state switch

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ocean

• Only coupled ocean-atmosphere-biosphere can
  explain intensity of change.
• Eolian records correspond with oceanic-atmospheric
  changes.

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The past becomes the present

• Two stable solutions
• Feedbacks maintain
• system
• Until next trigger
• forces pushes system

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Sahara-Sahel biodiversity

• History of Sahara is characterized by sudden
  change.
• Ecosystems reach climatic solution.
• Other regions also predisposed to regime shifts.
• Climate tolerance, evolutionary responses.

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Conclusion

• So if indeed it is reorganizations of ocean
  circulation that trigger jumps from one state of
  atmospheric operation to another, then by burning
  vast quantities of fossil fuels, we may be
  tampering with a very sensitive element in the
  Earths climate system (Broecker, 2000 139).

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Discussion

• Using the past to predict the future