Last Time - Short Term Climate Change

         Methods to Document Climate Change•

1.      Sedimentation• 2.      Ice cores• 3.      Dendrochronolgy• 4.      Coral Reefs• 5.      Pollen • 6.      Direct land and ocean measurements•

         Causes of Short-Term Change

• 1.      Volcanoes (atmospheric aerosols) …ex. Mt. Pinatubo• 2.      El Nino Southern Oscillation & La Nina• 3.      Solar Variability (sunspot 11 year cycle)

Past periods of climate change

Insert temperature recoreds

CO

2

The Medieval Warm Period

• 800 to 1300 AD• regional warming (not necessarily global)• Longer and warmer growing season

– grapes in England

• Higher treelines• Warmer sea surface temperatures in North

Atlantic• approx. 1o C warmer than present

         Recent Time Periods of Climate Change

1.      Medieval Warm Period (800-1300 AD)

2.      Little Ice Age (1450-1850 AD)

3. Dust Bowl (1940’s in North America)

Viking settlement on Iceland and Greenland from 800 to 1200

The Little Ice Age• Very cold climate between 1560 and 1850

• Greater frequency of storms

• Glacial advances 1560-1610,1816-1890

• Population declines in Iceland indicated by tax records

• shift from grains to barley (short growing season) to no grains

• fishing failed as fish migrated southward due to water temperatures.

• Height declines– from 5’8” in 900s to 5’6”

in 1700s in Iceland 0

100000

1000 1200 1400 1600 1800 2000

barley no grain

Iceland populationIceland

Greenland• 1300 highest

population (3000)• Poor harvests,

fewer livestock• Increase in sea ice

decreased trade• Settlements

abandoned• Height decrease

from 5’7” to < 5’ by 1400

         Recent Time Periods of Climate Change

• 1.      Medieval Warm Period (800-1300 AD)

• 2.      Little Ice Age (1450-1850 AD)

3. Dust Bowl (1930’s in North America)

Long Term Climate Change

Changes over hundreds of thousands to millions of years – Ice Ages

– Mesozoic Warm Period

Long Term Climate Change

Long Term Climate Change• Five Major Glacial

Periods in Earth’s History

Pleistocene - 15 myr to today

Permian - Carboniferous - 280 myr

Late Ordovician - 440 myr

Late Proterozoic - 800-600 myr

Huronian - 2200 -2500 myr

• How do we know this?• What causes Ice Ages?• Warm Mesozoic?

Evidence

• Geologic Record– Unconformities– Striations – Tillites

• Oxygen Isotopes for past 200 myrs

Pleistocene Ice Age

Cause of Ice Ages

• Many interacting factors including:

– Solar Radiation

– Greenhouse Effect - CO2 concentration

– Position of Land Masses/ Continents

Solar Radiation• Milutin Milankovitch - Serb astronomer /

mathematician described:

• Orbital variations that affect climate

• Esp. Summer insolation in the high latitudes …seasonal contrast

• Idea developed in 1920’s before the oxygen isotope record

•Milankovitch Cycles

–Precession

–Tilt

–Eccentricity

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?

Pleistocene Glaciations• General cool down in Cenozoic

– More chemical weathering - lower CO2

• Variations during this period seem to have a regular beat– Milankovitch Cycles

• Problem is largest temp shift is 100 kyrs but this is smallest orbital change– Need a feedback to amplify this signal– Look back at CO2 and the carbon cycle

The role of the earth’s surface:The Ice - Albedo Feedback

• Change amount of summer sun - Grow ice sheets - Change Albedo

• Change energy balance / temperature• Positive Feedback• Could explain amplification

Albedo Ice Sheets

Global TempSummer

Insolation

Cause of Ice Ages

Solar Radiation

Position of Land Masses/ Continents/ Ice

Greenhouse Effect - CO2 concentration

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 Variation

• Drop in CO2, where does it go?

• What can cause this variation of CO2 on this time scale(100 kyrs)?

• Geologic reservoirs?

• Biomass? During a glacial period?

• Oceans? Biological Pump?

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.

Biological Pump

• Change in marine productivity could explain changes in CO2

• How do we make ocean during glacial times more productive?

• Fertilize it. How?– Shelf Nutrient Hypothesis – Iron Fertilization

So…

Solar Radiation, Ice albedo feedback andAtmospheric CO2 changes

explain the cycle in ice ages

Mesozoic Warm Era• Much warmer at high

latitudes• Evidence from fossil

record • Oxygen Isotopes - deep

ocean 15 C (today it is 2 C)

• Thermohaline circulation ran backwards?

20 degrees warmer at the poles

Mesozoic Earth

• W - Warm Water Fossils

• E - Evaporites

• C - Coal Deposits

• Ocean much higher less land … why?

• Effect on albedo?

• Effect on carbon cycle?

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

• Look at this record...

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