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

Last Class Review Milankovitch Cycles –Precession –Tilt –Eccentricity Variations in CO 2 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?

CO 2 Variation From our ice core records we know that CO 2 changes rapidly Temperature matches CO 2 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

Oxygen Isotopes Foraminifera Shells - CaCO 3 Look at oxygen isotopes in these shell 18 O and 16 O 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 CO 2 –Slow down of mid- ocean ridge spreading –Uplift of Himalayas –Start of Asian Monsoon –Increased weathering Starting 30 myrs ago Big 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)

CO 2 Variation But from our ice core records we know that CO 2 changes also Temperature matches CO 2 change closely Chicken or Egg? Change in greenhouse effect Sharp Changes

CO 2 - The Human Influence Burning Fossil Fuels –60% of total Changes in land use –“Pioneer Effect” –Deforestation –Loss of organic matter in soil –40% of total EuropeN.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 CO 2 Burning fossil fuels - release CO 2 to atmosphere But CO 2 in atmosphere is increasing slower than the rate at which we are burning fossil fuels

Where is the missing CO 2 CO 2 is being transferred to another reservoir…. Rate is very fast… What carbon reservoirs are connected to atmospheric CO 2 with large fluxes?

Global CO 2 Variations Increasing trend with time Seasonal effect Larger in the N. Hemisphere Increase greater in N. Hemisphere

Atmospheric CO 2 Budget What we know –Rate of fossil fuel consumption (10%) –Atm. Increase (1%) What we don’t know very well –Deforestation –Greening –Ocean uptake

CO 2 Sinks The Ocean –Dissolution of CO 2 -> 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

CO 2 Feedback CO 2 Fertilization Increase CO 2 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 - CO 2 will rise in atmosphere to 720 ppm 100% efficient (i.e. use all nutrients CO 2 to 165 ppm CO 2 from atm.