Pleistocene Modern Climate

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Pleistocene Modern Climate
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Current grade scale
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Where we are in Geologic time
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Ceonzoic climate has fluctuated

• Changes in surface ocean temperature
• recorded in the O18/O16 ratio in the shells of
  planktonic foraminifera
• provide data about climatic events

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Oxygen Isotope Ratio
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Why the Icehouse?

• Long-term climate drivers
• Plate tectonics
• Opening/closing of seaways
• Ocean currents are our heat and AC
• Uplift and erosion of mountains
• Weathering reduces atmospheric CO2
• Life catastrophic evolution of new capabilities
• O2
• Astronomical drivers
• Other bodies (moon, sun) pull on the Earth,
  changing its distance to the sun

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Why the Pleistocene Icehouse ?

• Long-term tectonic driver
• Redirection of ocean currents
• Isolation of Antarctica
• Collision of N and S America
• New mountains more weathering
• Mineral weathering reduces atmospheric CO2
• less CO2 less greenhouse effect

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Antarctica became isolated ocean circulation
changes, cools
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Why the Icehouse?

• Shut off E/W global ocean flow
• Isthmus of Panama North South American plates
  collided 3.5 Ma

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Glaciers need precipitation

• Closing of Panama canal created Gulf Stream
  bringing warm moist water N

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Cenozoic cooling is here
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Expanded out
You are here
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The Milankovitch Theory

• Put forth by the Serbian astronomer
• Milutin Milankovitch while interned by
  Austro-Hungarians during WWI
• Minor irregularities in Earth's rotation and
  orbit
• are sufficient to alter the amount of solar
  radiation that Earth receives at 65 N
• and hence can change climate
• (criticism at the time why 65 N?!?)

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Three Variables
Ellipticity

• about 100,000 years

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Axis Tilt

• The angle between
• Earth's axis
• and a line perpendicular to the plane of its
  orbit around the Sun
• This angle shifts about 1.5
• from its current value of 23.5
• during a 41,000-year cycle

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Precession

• Earth moves around the Sun
• spinning on its axis
• which is tilted at 23.5 to the plane of its
  orbit
• Earths axis of rotation
• slowly moves
• and traces out the path of a cone in space

Plane of Earths Orbit
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Effects of Precession

• At present, Earth is closer to the Sun in January
• In about 11,000 years, closer to the Sun in July

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Why sensitive to insolation at 65 N?
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Ice-albedo feedback

• Albedo the reflectivity of a surface
• Percent reflected light/total incoming light

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Ice-albedo feedback
http//www.atmo.arizona.edu/students/courselinks/s
pring05/atmo336/lectures/sec5/iceage.html
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Climate atmospheric composition
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What makes a greenhouse gas?

• A greenhouse gas transmits light, but absorbs or
  emits infrared radiation (heat)

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Glass is a solid with greenhouse properties

• Closed car windows black leather seats in
  August.

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Current greenhouses

• Mars background 5C
• Earth background 33C
• Venus background 500 C!

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Water vapor is a climate feedback CO2 is a
greenhouse driver

• Water vapor is close to condensation point
• Earth T goes up --gt more water vapor
• Earth T goes down --gt less water vapor

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CO2 through the Pleistocene
http//www.earthsky.com/shows/profiles/alley.php
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(No Transcript)
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Last 100 years
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Stability and instability of the climate system
the Younger Dryas
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Earth system hiccupped coming out of the last
glaciation
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Oceanic conveyor
http//www.clivar.org/publications/other_pubs/cliv
ar_transp/powerpoint_fig/conveyer_new.gif
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Lake Agassiz collapse
WS Broecker, Fossil fuel CO2 and the Angry
Climate Beast, 2004
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Oceanic conveyor
http//www.clivar.org/publications/other_pubs/cliv
ar_transp/powerpoint_fig/conveyer_new.gif
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Last 100 years
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Modern atmospheric CO2
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Atmospheric CO2 sources

• NET Fossil fuel combustion 6x109 tons/year
• NET biosphere ZERO
• Gross biosphere 60x109tons/year in and out
• will CO2 make trees grow faster?
• A little, but not enough to bail us out.
• Especially if we keep cutting them down!

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Current climate trends
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Current climate trends
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Whats the future?