review: wednesday 5:30 –6:30, harshbarger 206. last class review milankovitch cycles –precession...
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Review: Wednesday 5:30 –6:30, Harshbarger 206
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Last Class• Review Milankovitch Cycles
– Precession
– Tilt
– Eccentricity
Variations in CO2 and Climate
Using Oxygen isotopes to reconstruct climate
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Eccentricity
• Cycle - 100,000 yrs• Elliptical - Circular• Changes total solar
flux by 0.2% • Does not affect
seasonal contrast• Optimum for
glacial period?
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Tilt
• Cycle - 41,000 yrs• More tilt - more
sun in summer - less in winter
• Changes seasonal contrast
• Optimum for glacial period?
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Precession• Cycle - 23,000 yrs• Precession of the
equinoxes• Due to wobble of the
axis• Impact due to elliptical
nature of orbit• Optimum for glacial
period?
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CO2 Variation• From our ice core
records we know that CO2 changes rapidly
• Temperature matches CO2 change closely
• Chicken or Egg?
• Change in greenhouse effect
Sharp Changes
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Stable Isotopes • Isotopes - same number of protons different
number of neutrons• Radioactive Isotopes - decay - age dating• Stable Isotopes - do not decay but ….• Due to difference in mass they react at different
rates in chemical processes such as evaporation, photosynthesis, etc…
• Leads to variations in the ratio of these stable isotopes
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Stable Isotope Notation• Express variation as per mil differences from a
standard
• Called delta values• Positive, relatively more of the heavy isotope• Negative more of the lighter isotope
18O 18O/16O sample 18O/16O s tan dard
18O /16O s tan dard
*1000
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Oxygen Isotopes
• Foraminifera Shells - CaCO3
• Look at oxygen isotopes in these shell
• 18O and 16O
• The colder the water the more oxygen-18 incorporated in the shell
• Use oxygen isotopes as a “paleo-thermometer – idea developed by Urey in the 1950’s
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Cenozoic Cool
• Why? Decrease CO2
– Slow down of mid-ocean ridge spreading
– Uplift of Himalayas– Start of Asian
Monsoon– Increased weathering
Starting 30 myrs agoBig cool down
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Forams and Oxygen Isotopes
• Two types of forams
• What does each tell us?
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Oxygen Isotope Record
• Benthic Forams - deep water temp• Long term trend• Short term trend• Causes?
Warmer
Colder
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Absorption Spectra of Atmospheric Gases
Anthes, p. 55
WAVELENGTH (micrometers)
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CO2 Variation• But from our ice core
records we know that CO2 changes also
• Temperature matches CO2 change closely
• Chicken or Egg?
• Change in greenhouse effect
Sharp Changes
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CO2 - The Human Influence
• Burning Fossil Fuels
– 60% of total
• Changes in land use
– “Pioneer Effect”
– Deforestation
– Loss of organic matter in soil
– 40% of totalEurope N.A.
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Fossil Fuels
• Always increasing…
• Presently around 6 – 7 Gtons
• Europe, N.America and China account for almost all of this
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Fossil Fuels and Atmospheric CO2
• Burning fossil fuels - release CO2 to atmosphere
• But CO2 in atmosphere is increasing slower than the rate at which we are burning fossil fuels
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Where is the missing CO2
• CO2 is being transferred to another reservoir….
• Rate is very fast…
• What carbon reservoirs are connected to atmospheric CO2 with large fluxes?
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Global CO2 Variations • Increasing
trend with time
• Seasonal effect
• Larger in the N. Hemisphere
• Increase greater in N. Hemisphere
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Atmospheric CO2 Budget
What we know– Rate of fossil fuel
consumption (10%)– Atm. Increase (1%)
• What we don’t know very well– Deforestation– Greening– Ocean uptake
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CO2 Sinks
• The Ocean – Dissolution of CO2 -> carbonic acid ->
bicarbonate-> carbonate
• Reforestation - Northern Hemisphere– Northeast US 1850’s ~20% forest - today ~80%– 0.5 Gtons C/yr in northern hemisphere
• Fertilize Existing Forest– The “Greening” of the earth
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CO2 Feedback
• CO2 Fertilization• Increase CO2 in atmosphere• Photosynthesis goes faster• But many other things limit biomass production
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Biological Pump
• What if we change how efficient this is?
• Turn it off - CO2 will rise in atmosphere to 720 ppm
• 100% efficient (i.e. use all nutrients
• CO2 to 165 ppm
CO2 from atm.