Review: Wednesday 5:30 –6:30, Harshbarger 206

Last Class• Review Milankovitch Cycles

– Precession

– Tilt

– Eccentricity

Variations in CO2 and Climate

Using Oxygen isotopes to reconstruct climate

Eccentricity

• Cycle - 100,000 yrs• Elliptical - Circular• Changes total solar

flux by 0.2% • Does not affect

seasonal contrast• Optimum for

glacial period?

Tilt

• Cycle - 41,000 yrs• More tilt - more

sun in summer - less in winter

• Changes seasonal contrast

• Optimum for glacial period?

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?

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

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

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

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

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

Forams and Oxygen Isotopes

• Two types of forams

• What does each tell us?

Oxygen Isotope Record

• Benthic Forams - deep water temp• Long term trend• Short term trend• Causes?

Warmer

Colder

Absorption Spectra of Atmospheric Gases

Anthes, p. 55

WAVELENGTH (micrometers)

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

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.

Fossil Fuels

• Always increasing…

• Presently around 6 – 7 Gtons

• Europe, N.America and China account for almost all of this

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

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?

Global CO2 Variations • Increasing

trend with time

• Seasonal effect

• Larger in the N. Hemisphere

• Increase greater in N. Hemisphere

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

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

CO2 Feedback

• CO2 Fertilization• Increase CO2 in atmosphere• Photosynthesis goes faster• But many other things limit biomass production

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.