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Last Time - Short Term Climate Change

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

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Last Time - Short Term Climate Change

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  1. 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)

  2. Past periods of climate change Insert temperature recoreds CO2

  3. 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

  4. ·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)

  5. Viking settlement on Iceland and Greenland from 800 to 1200

  6. The Little Ice Age • Very cold climate between 1560 and 1850 • Greater frequency of storms • Glacial advances 1560-1610,1816-1890

  7. Iceland Iceland population • 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 barley no grain

  8. 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

  9. ·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)

  10. Long Term Climate Change Changes over hundreds of thousands to millions of years • Ice Ages • Mesozoic Warm Period

  11. Long Term Climate Change

  12. Five Major Glacial Periods in Earth’s History Long Term Climate Change 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?

  13. Geologic Record Unconformities Striations Tillites Oxygen Isotopes for past 200 myrs Evidence

  14. Pleistocene Ice Age

  15. Many interacting factors including: Solar Radiation Greenhouse Effect - CO2 concentration Position of Land Masses/ Continents Cause of Ice Ages

  16. 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 Solar Radiation

  17. Milankovitch Cycles • Precession • Tilt • Eccentricity

  18. Cycle - 100,000 yrs Elliptical - Circular Changes total solar flux by 0.2% Does not affect seasonal contrast Optimum for glacial period? Eccentricity

  19. Cycle - 41,000 yrs More tilt - more sun in summer - less in winter Changes seasonal contrast Optimum for glacial period? Tilt

  20. 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? Precession

  21. 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

  22. Change amount of summer sun - Grow ice sheets - Change Albedo Change energy balance / temperature Positive Feedback Could explain amplification The role of the earth’s surface:The Ice - Albedo Feedback Summer Insolation Global Temp Albedo Ice Sheets

  23. Solar Radiation Position of Land Masses/ Continents/ Ice Greenhouse Effect - CO2 concentration Cause of Ice Ages

  24. But from our ice core records we know that CO2 changes also Temperature matches CO2 change closely Chicken or Egg? Change in greenhouse effect CO2 Variation Sharp Changes

  25. 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? CO2 Variation

  26. 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 Biological Pump CO2 from atm.

  27. 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 Biological Pump

  28. So… Solar Radiation, Ice albedo feedback and Atmospheric CO2 changes explain the cycle in ice ages

  29. Much warmer at high latitudes Evidence from fossil record Oxygen Isotopes - deep ocean 15 C (today it is 2 C) Thermohaline circulation ran backwards? Mesozoic Warm Era 20 degrees warmer at the poles

  30. W - Warm Water Fossils E - Evaporites C - Coal Deposits Ocean much higher less land … why? Effect on albedo? Effect on carbon cycle? Mesozoic Earth

  31. 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 Isotopes

  32. 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 Stable Isotope Notation

  33. 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 Oxygen Isotopes

  34. Cenozoic Cool Starting 30 myrs ago Big cool down • Why? Decrease CO2 • Slow down of mid-ocean ridge spreading • Uplift of Himalayas • Start of Asian Monsoon • Increased weathering • Look at this record...

  35. Two types of forams What does each tell us? Forams and Oxygen Isotopes

  36. Benthic Forams - deep water temp Long term trend Short term trend Causes? Oxygen Isotope Record Warmer Colder

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