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Pleistocene + Modern Climate
Current grade scale
percent
9 2 -1 0 0
9 0 -9 1
8 8 -8 9
8 2 -8 7
8 0 -8 1
7 8 -7 9
7 2 -7 7
7 0 -7 1
6 8 -6 9
6 2 -6 7
6 0 -6 1
0 -5 9
grade
A
AB+
B
BC+
C
CD+
D
DF
Where we are in
Geologic time
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
Oxygen Isotope Ratio
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
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
Antarctica became
isolated:
– ocean circulation
changes, cools
Why the Icehouse?
• Shut off E/W global ocean flow
Isthmus of Panama: North & South
American plates collided ~ 3.5 Ma
Glaciers need precipitation
• Closing of
Panama canal
created Gulf
Stream
bringing warm
moist water N
Cenozoic cooling is here
Expanded out:
You are here
The Milankovitch Theory
• Put forth by the Serbian astronomer
– Milutin Milankovitch while interned by AustroHungarians 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?!?)
Three Variables
Ellipticity
• about 100,000 years
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
Precession
• Earth moves
around the Sun
– spinning on its
axis
– which is tilted at
23.5° to the plane
of its orbit
• Earth’s axis of
rotation
– slowly moves
– and traces out
the path of a
cone in space
Plane of Earth’s Orbit
Effects of Precession
• At present, Earth is closer to the Sun in January
• In about 11,000 years, closer to the Sun in July
Why sensitive to insolation at
65° N?
Ice-albedo feedback
• Albedo: the reflectivity of a surface
– Percent reflected light/total incoming light
s urfac e
s and
gras s
fores t
water
fres h s now
thic k c loud
albedo
0 .2 0 - 0 .3 0
0 .2 0 - 0 .2 5
0 .0 5 - 0 .1 0
0 .0 3 - 0 .8 0
0 .8 0 - 0 .8 5
0 .7 0 - 0 .8 0
Ice-albedo feedback
http://www.atmo.arizona.edu/students/courselinks/spring05/atmo336/lectures/sec5/iceage.html
Climate: atmospheric composition
major atmos . gas es
nitrogen, N2
oxygen, O2
A rgon, A r
water vapor, H
2O
c arbon dioxide, C2O
% by volume
78%
21%
0 .9 0 %
0 .0 0 0 0 0 1 - 4 %
0 .0 3 7
major greenhous e
gas es
water vapor, H
2O
c arbon dioxide, C2O
methane, C H
4
nitrous oxide, N
2O
ozone, O3
freon- 1 1 , C C
3Fl
freon- 1 2 , C C
2Fl 2
parts per million
(ppm)
0 .1 - 4 0 ,0 0 0
370
1 .7
0 .3
.0 .1
0 .0 0 0 2 6
0 .0 0 0 5 4
What makes a greenhouse gas?
• A greenhouse gas transmits light, but
absorbs or emits infrared radiation (heat)
Glass is a solid with greenhouse
properties
• Closed car windows + black leather
seats in August….
Current greenhouses
• Mars: background +5°C
• Earth: background + 33°C
• Venus: background +500 °C!
Water vapor is a climate feedback;
CO2 is a greenhouse driver
• Water vapor is close to condensation
point:
– Earth T goes up --> more water vapor
– Earth T goes down --> less water vapor
CO2 through the Pleistocene
http://www.earthsky.com/shows/profiles/alley.php
Last 100 years
Stability and instability of the
climate system: the Younger Dryas
Earth system hiccupped coming out
of the last glaciation
Oceanic conveyor
http://www.clivar.org/publications/other_pubs/clivar_transp/powerpoint_fig/conveyer_new.gif
Lake Agassiz collapse
WS Broecker, Fossil fuel CO2 and the Angry Climate Beast, 2004
Oceanic conveyor
http://www.clivar.org/publications/other_pubs/clivar_transp/powerpoint_fig/conveyer_new.gif
Last 100 years
Modern atmospheric CO2
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!
Current climate trends
Current climate trends
What’s the future?