Temperature/Precipitation History Faint Young Sun paradox: Fig 12-2

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1 Mon May 8 Announcements: grades through midterm posted (but several extra credit reports not recorded) "Snowball Earth" article available, but not required Great website: " Where we're going: This week: "Ancient Climates" (Chap 12 and a little from Chap 11) begin "Recent Climates" (Chap 14 and 15, selected) ** see "Schedule/Readings" button on class website ** Wed: HW#4 DUE Ancient Climates: Readings see Schedule/Readings button on class website Chap 12 (all) Long-term Climate Regulation Chap 11 Rise of Oxygen (p.212) Modern Controls on Atmospheric Oxygen (p , Fig 11-22) Snowball Earth supplemental material web page: Scientific American article available on class website Snowball Earth book by Gabriele Walker, 2003 end of last ice-age; begin civilization beginning of modern era of ice-ages asteroid impact; end of dinosaurs Cambrian explosion of life; beginning of fossil record Earth freezes over; life survives in pockets rise of atmospheric oxygen (greatest global pollution event; deadly to nearly all existing life) life! (prokaryotic bacteria) Geological Time: Fig 12-8 Ice-ages asteroid! coal/oil Dinosaurs formation of Earth Earth is unfathomably old most of Earth history is very alien Geological Time: Fig 12-8 Cambrian explosion Temperature/Precipitation History Faint Young Sun paradox: Fig 12-2 solar energy simple model of Earth's temperature model assumes: - CO2 in atmosphere same as today - Earth albedo same as today Question: Why do we know this model is wrong? Answer: Because life formed around 4 billion years ago (see next slide) and has existed on Earth ever since. Life requires liquid water. 1

2 Answer: Archeon life! Requires liquid water Fig 10-7: microfossils, 3.5 billion yr old, Australia Tues May 9 Upcoming Talks: Tues 12:30, 310 ATG, weather roundup Wed 12:30, Savery 209, Psychology of weather forecast information Wed 7 pm, Kane 120, Re-birth of environmentalism Thurs 3:30, Mary Gates Hall 258, What do we owe future generations? Thurs 3:30, JHN 102, Glaciers, Climate... in the Himalaya Fri 3:30, JHN 075, Are El Nino episodes becoming more common? Today: Faint Young Sun Marker Events Mesozoic Warmth and Cenozoic Cooling [Sister planets] Wed: Thurs: HW#4 DUE Snowball Earth begin "Recent Climates" Actual (Earth History) Headlines Actual (Earth History) Headlines 4.6 billion ybp (years before present): A new planet forms! ~ 4 billion ybp: Earth acquires life! ~ 2 billion ybp: Poisonous oxygen gas rises to critical levels; further increase appears unstoppable! million ybp: Entire planet freezes over! Life appears doomed 540 million ybp: Life explodes in multicellular diversity! 65 million ybp: Massive Asteroid Strikes Earth; Dinosaur era ends! 3 million ybp: Cooling Earth Enters New Era of Alternating Ice-Ages and Interglacials 10,000 ybp: Ice-Age Glaciers Melt; A New Interglacial Period Begins Faint Young Sun paradox: p paradox: despite less solar energy, Archean was warm enough to support photosynthetic life Possible explanations - sun...? - albedo... no - geothermal energy... no > greenhouse... - H2O... no - NH3... no > CO2... [see figure] less land more volcanism conceptual framework: T s = f(s o, A, T g ) plenty of carbon [see inorganic carbon cycle figure] > CH4 methane? (CH4) [recent Kasting proposal] early life would have produced it far longer atmospheric lifetime than today due to lack of oxygen Fig 12-2 Amount of CO 2 needed to make Earth at least partly ice-free in the past 10 bar = 1/6 Of all C in limestone 0.1 bar = 300X present CO2 (80+ C for bacteria) Illustrates nature of scientific knowledge/progress 2

3 Is that much CO 2 possible? Possible Archaen feedback If early bacteria produced CH 4 and loved heat. Rocks could supply 60 bars of CO 2 to atmosphere (so yes!) (Some bacteria today have these characteristics) Fig 8-3 Earth History: Marker Events: In-Class Activity 1. Origin of Earth 4.6 billion ybp (years before present) Mesozoic Warmth/ Cenozoic Cooling KKC Origin of Life ~4 billion ybp Cenozoic Cooling 3. Rise of Oxygen to ~ modern levels ~2 billion ybp Mesozoic Warmth 4. Snowball Earth events million ybp 5. Beginning of fossil record (Cambrian explosion) 540 million ybp 6. Extinction of Dinosaurs by asteroid 65 million ybp 7. Beginning of modern glaciations 3 million ybp Fig End of last ice-age 10 thousand ybp Arrhenius, 1896 Mesozoic and Early Cenozoic Warmth: million ybp (overheads) What: - Warmer global-mean temperature. - Much warmer Polar Regions; no ice-caps. - Much warmer deep ocean. Evidence: - Lush ferns and alligators in Siberia. - Carbon isotopes in ocean sediments Cause: - Higher CO2 is leading suspect. - sea-floor spreading rate was greater - higher sea level (no ice caps) Remaining mysteries: - Ocean/atmos heat transport must have been much more efficient. - latitudinal and vertical - this is not understood Fig

4 What: - Earth cools, beginning ~60 million ybp. - Life retreats from Poles. - Polar ice caps form. - Eventually, ice-ages begin. Cause (one leading theory): - India collides with Asia. - Himalayas form. - Silicate weathering increases. - Atmospheric CO2 goes down. Cenozoic cooling: 40-3 million ybp Upcoming Talks: Wed 12:30, Savery 209, Psychology of weather forecast information Wed 7 pm, Kane 120, Re-birth of environmentalism Thurs 3:30, Mary Gates Hall 258, What do we owe future generations? Thurs 3:30, JHN 102, Glaciers, Climate... in the Himalaya Fri 3:30, JHN 075, Are El Nino episodes becoming more common? Today: Sister Planets Snowball Earth Thurs: begin recent climates Wed May 10 Fig Venus (runaway greenhouse) Sister planets (Ch 19, p ) Earth ("just right") Mars (virtually no greenhouse) Mars (virtually no greenhouse) Mars, CO2 and Greenhouse - CO2 is ~10 times Earth - T g = ~3C - Oceans boiled away -has oceans - No more weathering - Carbon partitions to atmosphere - CO2 is ~100,000 times that on Earth -T s = 427 C; T g = 466C - hydrological cycle - weathering returns CO2 to lithosphere - plate tectonics (volcanoes) return carbon to atmos. - negative feedback - farther from Sun; too cold for liquid water - no water vapor greenhouse - too small for plate tectonics - no carbon cycle - CO2 is ~10 times Earth -T s = -53C; T g = ~3C Do you notice something strange about these facts??? What can we conclude about the cause of the greenhouse effect on Earth??? Hoffmann, Schrag, and Dropstone Snowball Publications Snowball Compendium: 1.4: Histogram of papers relating to Precambrian glacials and glaciation by year of publication (445 papers) from 1930 to

5 Snowball Science History -1 Budyko Model: Multiple Steady States 1960's: Mikhail Budyko (theoretical climate modeling) "run-away" ice-albedo feedback if Earth freezes below 30-degree latitude this must never have happened for two reasons... Anti-Snowball arguments: 1. Continuous life 2. Earth could never recover 1964: Brian Harland (geologist) Late proterozoic glacial deposits on almost every continent magnetic alignment of grains indicate continents were near Equator 7.3: Ice-line latitude on an all-ocean planet as a function of Solar flux or equivalent pco 2, based on a simple energy-balance model of the Budyko-Sellers type. Under the present Solar flux (1.0), three stable climate states are possible, all ice (blue), no ice (red) and small ice (yellow). Large ice (open circle) is unstable and spontaneously falls to all ice. Black arrows indicate jumps in the CO 2 hysteresis loop of a snowball earth cycle. ice-albedo feedback Geological Sites Showing Evidence of Glaciations Fig 3-21 Positive feedback loop: - amplifies an initial perturbation - potentially causes current equilibrium state to be unstable 1.7: Present global distribution of younger ( Marinoan ) Cryogenian (ca Ma) glacial and glacial-marine deposits. Red dots indicate deposits that include banded iron or iron-manganese formations (BIF). Earth's Magnetic Field Possible continental positions during Late Proterozoic Glaciations: Fig Critical latitude for "runaway" ice-albedo (~30 degrees): Why would ice-albedo feedback get stronger as the ice-line got to lower and lower latitudes??? Answer: - more sunlight to reflect at lower latitudes - the amount of area per degree latitude gets much larger (major factor) 5

6 Snowball Science History -2 Anti-Snowball arguments: 1. Continuous life 2. Earth could never recover 1960's: Martin Rudwick (biologist) with Brian Harland Recovery from global glaciation may have spurred Cambrian explosion "all 11 animal phyla ever to inhabit the earth emerged within a narrow window of time" after the end of the last glaciation geological carbon cycle: picture 1970's: more biology discovery of life in extreme environments organisms near geothermal vents at ocean bottom have no need of sunlight bacteria and algae living in snow, ice, and rock pores under extreme cold, heat, and pressure overcomes argument (1), above 1992: Joseph Kirschvink (geophysicist) Atmospheric CO2 would build up during a global glaciation CO2 removal by silicate weathering would cease, but CO2 input from volcanoes would continue unabated overcomes argument (2), above volcano in ice-covered world snowball carbon cycle More Questions 1. What is the major greenhouse gas in the present climate? 2. Use this fact to expand on the argument that it would be very difficult for Earth to recover from and ice-covered ("snowball") state. Answers: 1. Water vapor 2. Colder temperatures (about -50C) would mean far less water vapor in the atmosphere, thus almost no greenhouse effect at all. Thus, it would take a huge amount of CO2 to overcome the deficit and raise the temperature back above freezing. Snowball Science History : Kenneth Caldeira and James Kasting Calculate that CO2 would have to be 350 times current levels to melt a global glaciation This would take about 10 million years 1992: Joseph Kirschvink Iron deposits mixed with glacial debris indicate ocean lacked oxygen This implies ice-covered oceans 1990's: Hoffman and Schrag Carbon isotopes in rocks surrounding glacial deposits indicate a virtual shut-down of biological activity Massive carbonate deposits on top of the glacial deposits ("cap carbonates") indicate very warm water and sudden deposition of huge amounts of carbon Apparently, the glaciation events were immediately followed by a global hothouse period This is consistent with huge buildup of atmospheric CO2. 6

7 Idealized carbon isotope record through a Snowball event Measured carbon isotope record through a Snowball event Ghaub Glaciation, Otavi Group, NW Namibia Iron Solubility and Deposition in Relation to a Snowball Event banded-iron formations banded-iron formation Namibia cliffs, snowball record 7

8 Evidence: 13-Carbon etc snowball sequence Thurs May 11 Welcome Thunderbirds! banded-iron formation Why are the banded iron formations "banded"? If the ice melted rapidly and in a single, global-scale event, all the iron should be laid down in a single band! This data looks like multiple, global glaciations over very short time periods! Upcoming Talks: Thurs 3:30, Mary Gates Hall 258, What do we owe future generations? Thurs 3:30, JHN 102, Glaciers, Climate... in the Himalaya Fri 3:30, JHN 075, Are El Nino episodes becoming more common? Today: wrap-up: Snowball Earth begin: Recent Climates Tentative answer (see KKC p224): Dissolved iron builds up in the deep ocean (emitted from hydrothermal vents). It remains there long after the melting. These sediments are from continental margins. The deep water gets mixed into the shallow water at continental margins in pulses. geological carbon cycle: picture Geological Carbon Cycle Fig 8/18 8

9 Paleoclimate: why study? We address questions like Has climate changed in the past? How much? How fast? The answers provide a context for assessing human-induced climate change (e.g. global warming). Paleoclimate studies may give us insights into - mechanisms of climate change - functioning of the Earth system - stabilizing or amplifying feedbacks "Recent" Climates: Readings KKC focus topics Chap 14: Geological Evidence of glaciations Milankovitch Cycles (orbital theory) Glacial-climate feedbacks Chap 15: "Introduction" "Volcanoes and Climate" "Solar Variability" "El Nino-Southern Oscillation" pages 14: : : : : : : Figures 14-2, 14-3, , 14-6, , , , Old edition of textbook KKC focus topics for old, 1st edition Chap 11: Geological Evidence of glaciations Milankovitch Cycles (orbital theory) Glacial-climate feedbacks Chap 12: "Introduction" "Volcanoes and Climate" "Solar Variability" "El Nino-Southern Oscillation" Glaciation Map pages 11: : : : : : : Figures 11-2, 11-3, , 11-7, , , , Ice-Cover During Last Ice Age Puget Sound buried from Olympics to Cascades Map: Lake Missoula Floods Pleistocene Glaciations: OVERVIEW Geological evidence abundant, overwhelmingly convincing timing info is not precise (recall Ahrrenius, 1896) Ocean sediments 18O provides record of glacial ice amount detailed, precise timing information timing seems to correspond to orbital parameters Ice-core record 18O provides record of local temperature air bubbles provide record of CO2 and other gases remarkable correlation between temperature and CO2 Orbital parameters precession (23 k.y.), tilt (41 k.y.), eccentricity (100 k.y.) Cause of glacial oscillations (theory) orbital trigger involving N. Hem. Summer ice-albedo feedback CO2 as contributing driver Problems eccentricity: tiny trigger but dominant oscillation timing not always logical for specific events lapse rate in the Tropics 9

10 Pleistocene Glaciations: LESSONS 1. Current climate is not the only possible one for Earth (indeed, glacial conditions seem to be preferred) 16 O vs 18 O "light" (normal) "heavy" Isotopic Evidence (updated version of Fig 11-3) evaporation selects for "light" condensation (precipitation) selects for "heavy" 2. A change in global-mean surface temperature of about -5C is associated with a massive climate shift 3. Global climate and CO 2 appear to be intimately intertwined 4. If the orbital parameter theory is right, small triggers can produce major climate changes under some conditions 5. And there are many remaining questions and enigmas 18 O in ocean sediments records glacial ice volume: More "light" water in ice-sheets means remaining ocean water is "heavier". 18 O in ice-cores indicates local temperature: Colder conditions means more precipitation en route so "lighter" snow. 3.5 Million Year Record of Global Ice Volume 3.5 Million Year Record of Global Ice Volume Oscillations get longer Ice-ages begin TIME Questions: 1. Is this an ocean sediment record or a polar ice-core record? 2. Which way does time go on this plot (left-to-right or right-to-left)? 1. Ocean sediments record ice volume. Ice-core records only extend back to about 500,000 years at most. TIME Questions: 3. What two major transitions do you see in this record? 4. Was sea-level lower or higher than today during the three most prominent previous interglacial periods? 4. Less ice-volume, therefore higher sea level. (May have been warmer than today as well.) Eccentricity 100,000 years Orbital Parameters Obliquity (or Tilt) 41,000 years Precession 26,000 years 10