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What we wish to learn Today:

What we wish to learn Today:. Past Climate Change and the Ice Ages. Paleoclimatology. 1. What do we mean by "paleoclimate"? 2. What evidence exists for ice ages and ancient climate change? What causes the climate to change?. 2. 1. N.H. Temperature (°C). 0. -1. 1400. 1000. 1200.

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What we wish to learn Today:

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  1. What we wish to learn Today: Past Climate Change and the Ice Ages Paleoclimatology • 1. What do we mean by "paleoclimate"? • 2. What evidence exists for ice ages and ancient climate change? • What causes the climate to change?

  2. 2 1 N.H. Temperature (°C) 0 -1 1400 1000 1200 1600 1800 2000 Year “Recent” climate change and variability… Mann et al. (1999) GRL 26:759-762

  3. 6 5 4 3 2 1 1 0.5 0 N.H. Temperature (°C) 0 -0.5 1000 1200 1400 1600 1800 2000 …provides perspective on where we are headed Global Temperature (°C) IPCC Projections to 2100

  4. 1856 1987 2000 We KNOW the climate has changed recently The great Aletsch glacier, Switzerland

  5. 2000 1970 15 10 Area (km2) 5 0 1900 1920 1940 1960 1980 2000 2020 Year Ice on Mt. Kilimanjaro L.Thompson, in prep.

  6. Glacial Changes since last Ice Age Ice and Trees Percent of Spruce in Total Trees

  7. Glacial Europe was treeless in the last ice age Vegetation in present day Europe is dominated by forest, with conifers in the north and deciduous trees in the south. At the glacial maximum, 20 thousand years ago, arctic tundra covered much of Europe south of the ice sheet, and only patches of forests remained near the southern coasts.

  8. Cenozoic Mesozoic Paleozoic PreCambrian Ancient Climates • Climate was warm during the Age of the Dinosaurs (the Mesozoic) • Alligators lived in Siberia! • Dinosaurs lived north of the Arctic Circle in Alaska!

  9. Methods to establish past climate • Isotopic Geochemical Studies: the study of rock isotopic ratios, ice core bubbles, etc. • Dendochronology: the study of tree rings • Pollen Distribution: the study of plant types and prevalence (e.g., Europe’s vegetation in the last ice age) • Lake Varves: (like dendochronology, but with lake sediments) • Coral Bed Rings:(like dendochronology, but with corals) • Fossils: Studies of geological settings, etc. • Historical documents: paintings of glaciers, etc.

  10. d18O ‰ = 18O/16O of sample - 18O/16O of standard  1000 18O/16O of standard Oxygen isotopes and paleoclimate • Oxygen has three stable isotopes: 16O, 17O, and 18O. (We only care about 16O and 18O) • 18O is heavier than 16O (it has 2 extra neutrons). • The amount of 18O compared to 16O is expressed using “delta” notation - the unit is “per mil” (parts per thousand): Fractionation: Natural processes tend to preferentially take up the lighter isotope, and preferentially leave behind the heavier isotope. For most chemistry, the isotopes behave the same.

  11. Isotope “fractionation” • Oxygen isotopes are fractionatedduring evaporation and precipitation of H2O • H216O evaporates more readily than H218O • H218O precipitates more readily than H216O • Oxygen isotopes are also fractionated by marine organisms that secrete CaCO3 shells. The organisms preferentially take up more 16O as temperature increases.

  12. 16O 16O 18O 18O 16O 18O 18O 16O 16O 16O 18O 16O Fractionation effects (1) Sea water is heavier than water vapor Precipitation favors H218O (2) cloud water becomes more depletedin H218O as it moves inland or poleward… Evaporation favors H216O H218O H218O Ice Land H216O, H218O Ocean (3) Snow and ice are depletedin H218O relative to sea water. 18O 18O 18O 16O 18O 18O 16O 18O 18O

  13. δ18O = -20 o/oo δ18O = -15 o/oo δ18O = -10 o/oo -11 o/oo -6 o/oo CaCO3 Carbonate sediments also record the signal of the ocean, and the signal of temperature Fractionation effects rain rain Ice Land δ18O = 0 o/oo Ocean

  14. Vostok Record We can also show that the d18O of precipitation is well correlated with temperature! So, if we know the d18O of water or ice, we know what the air temperature was at that time. (Note that hydrogen isotopes work the same way)

  15. The Antarctic Ice Coring operation at Vostok station The Greenland Ice Coring operation at Summit station

  16. Ice Core Analyses The ice can be analyzed for its 18O content to estimate temperature The air bubbles trapped in the ice can be analyzed for their carbon dioxide and methane content

  17. Ocean Sediment analysis Isotopes of organisms deep-sea foraminifera Growing glaciers δ18O = - 30 δ18O = - 35 Interglacial Ice • The “Ice Volume” effect • Light isotope removed from ocean, locked into large ice sheets • Remaining ocean water was +1.5‰ heavier in 18O, as recorded in marine organism shells (CaCO3) • Ocean level was ~120 m lower than today δ18O = 0.0 Glacial Ice δ18O = 1.5

  18. Possible Causes of Climate Change • Long-Term • Solar Luminosity • Shifting Continents • Greenhouse gases • Medium-Term • Orbital parameters • Greenhouse gases • Short-Term • Greenhouse gases • Sunspots • Ocean currents Power: 4 x 1026 W 2 x 1017 W

  19. 1 6 . 1 . 4 1 . 2 Luminosity 1 0 . 8 0 . 6 0 2 4 6 8 1 0 Time (billions of years) . Evolution of our Sun‘s Luminosity Today Snowball Earth ?

  20. Today’s configuration Shifting land masses (by plate tectonics) may have changed greenhouse gas concentrations, thus affecting climate Past configurations

  21. As the continents shift there is increased subduction and volcanic activity which increases CO2 into the atmosphere That atmospheric CO2 is then consumed in weathering reactions on continents, and eventually returned to the ocean. This is the long-term “weathering” control of climate.

  22. Silicate weathering From C. Poulsen’s lecture, 24 Sep • CO2 + H2O  H2CO3 (carbonic acid) • CaSiO3 + 2H2CO3 Ca2+ + 2HCO3- + SiO2 + H2O (silicate weathering) • Ca2+ + 2HCO3-  CaCO3 + H2CO3 (carbonate precipitation & burial) Net: CaSiO3 + CO2  CaCO3 + SiO2 Conversion of CO2 gas to limestone! H2CO3 H2CO3 Ca2 Ca2 Ca3SiO3 Ca3SiO3 CO2 CO2

  23. Orbital forcing (Milankovitch) 1.Shape (eccentricity, ~100K and 400K yrs) 2.Tilt (obliquity, ~41,000 yrs = 41K yrs) 3.Wobble (precession, ~23K yrs) 1879-1958

  24. Interaction of orbital periods give different patterns of change.The magnitude of shifts in solar insolation are large enough to explain changes in climate

  25. ~ 23ky 0 -10 -20 Tilt 41ky Milankovitch Forcing Explains Ice Core Data 1000s of years Before Present ( kyr B.P. )

  26. d18O in Chinese caves and insolation Orbital forcing GISP2 Ice Core 1000s of years Before Present ( kyr B.P. ) D. Yuan et al., Science 304, 575

  27. -5 order chaos -10 order chaos -5 -10 -15 -20 Greenland What causes rapid and unpredictable changes in climate? Antarctica 1000s of years Before Present ( kyr B.P. )

  28. Causes of Climate change A. Tectonic B. Orbital C. ?? D. ??

  29. Summary Past changes in climate have been dramatic on Earth The longest-term changes (100s Million years, Ma) are driven by shifting continents and interactions with greenhouse gases. At medium time scales (1-10s Ma), changes are triggered by variations in orbital characteristics. Take-home point: “If you don’t like the climate, hang around awhile…”

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