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. 1 o C warmer than present

 Recent Time Periods of Climate Change 1. Medieval Warm Period ( AD) 2. Little Ice Age ( 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 ,

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 barleyno grain Iceland population Iceland

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 ( AD) 2. Little Ice Age ( 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

Five Major Glacial Periods in Earth’s History Pleistocene - 15 myr to today Permian - Carboniferous myr Late Ordovician myr Late Proterozoic myr Huronian 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 - CO 2 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 CO 2 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 CO 2 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 AlbedoIce Sheets Global Temp Summer Insolation

Cause of Ice Ages Solar Radiation Position of Land Masses/ Continents/ Ice Greenhouse Effect - CO 2 concentration

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 Variation Drop in CO 2, where does it go? What can cause this variation of CO 2 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 - 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.

Biological Pump Change in marine productivity could explain changes in CO 2 How do we make ocean during glacial times more productive? Fertilize it. How? –Shelf Nutrient Hypothesis –Iron Fertilization

So… Solar Radiation, Ice albedo feedback and Atmospheric CO 2 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

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 Look at this record... 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