Guide Study for Final Exam Chapter 12: Long-Term Climate Regulation Faint Young Sun Paradox During early parts of Earth's history, faintness of young sun probably offset by higher concentrations of greenhouse gases CO2 dominated at first CH4 also important Produced by methanogenic bacteria Combination of CO2 and CH4 kept Earth warm until early Paleoproterozoic Era O2 increased about 2.3 BY ago Eliminated most CH4 Triggered 1st major glaciations Since then, climate balanced by increased solar luminosity and decreased CO2
Importance of CO2 and CH4 in Archean Climate ~3.8 to 2.3 BY ago High CO2 levels not needed if CH4 abundant Abundant CH4 leads to decreased CO2 because warming results in faster silicate weathering
Pink Sky During Archean O2 and N2 scatter blue light CH4 and CO2 scatter orange/red light CH4 polymerized to form higher hydrocarbons Long chains Mie scattering: scattering by particles comparable in size to wavelengths of solar radiation Mars Organic haze formed (+) feedback loop: Increased tempt Faster-growing methanogens Increased methane production Greater greenhouse effect Increased surface temps Archean climate: CO2 and CH4 levels comparable
Anti-Greenhouse Effect
Absorption of sunlight (and radiation of IR energy) by particles or gases high up in Stratosphere. Prevents sunlight from reaching surface Causes surface cooling CO2 levels actually low in Archean Caused by hydrocarbon smog (-) feedback loop: Smog cools Earth Decreased methane production Thinner smog layer Heating of Earth Increased methane production Thicker smog layer Regulated temps in Archean era
3 Major Geological Indicators for Glaciation on BY Timescales Evidence from geologic deposits formed by glacial ice 1. Tillites: mixtures of cobbles, pebbles, sand and mud that have been packed together to form rocks Formed from debris produced when glaciers grind up surface rocks 2. Moraines: piles of rubble along margins of ice sheets Deposited after debris is carried along by glaciers as they move 3. Dropstones: misplaced chunks of rock Formed when rocks trapped in glacial ice are carried out to sea by icebergs Process called "ice-rafting" Glacial striations: long, parallel scratches in rocks formed when moving glaciers drag other rocks across surface
Long-Term Glacial Record 5 major glaciations periods: 1. Huronian 2. Late Proterozoic 3. Late Ordovician 4. Permo-Carboniferous 5. Pleistocene
Geologic Indicators of Paleoclimate Measuring oxygen isotopes in carbonate sediments obtained from deep-sea cores Only more recent timescales
Fossil records Species that can live in certain climates Drawbacks: Continents have drifted Single-cell organisms could survive in multiple climates
Snowball Earth Late Proterozoic glaciations (-) feedback loop: Increased CO2 Increased temp Increased silicate weathering Decreased CO2 Decreased temp Low-latitude glaciations Lower solar luminosity Global glaciations require continents at low latitudes
Most Recent Glaciation Pleistocene 1.8 MY ago
Climate Regulatory Mechanisms Faint young sun vs. more greenhouse gases Increasing solar luminosity vs. decreasing CO2 Negative feedback associated with carbonate-silicate cycle
Mesozoic Warming Age of dinosaurs from Evidence fossils and deep-sea cores Increased CO2 levels Faster sea spreading Less land available to weather silicate rocks Other possible influences: less temp contrast between equator and poles heat transfer more efficient Hadley cells extend further poleward than today
Cenozoic Cooling 30 MY ago Initially, reduced sea spreading rates
Reduced CO2 Silicate weathering enhanced by plate tectonics
Chapter 15: Short-Term Climate Variability Climate Variability Climate change: Long timescales; slow Between 2 time spans Climate variability: short timescales, faster
Proxy Data Proxy data: cannot be directly observed, but can be inferred from other evidence Palynology: study of pollen and organic microfossils Dendrochronology: dating trees by counting rings
Holocene Geological epoch extending from 10,000 years ago to present Interglacial interval Mid-high latitudes: greater temp. change Tropics-subtropics: greater moisture change
Younger Dryas Earth began to warm 10,000~15,000 years ago Vegetation colonized Spread of milder conditions Triggered by diversions of meltwater in N. America N. Atlantic deep-water formation reduction Happened in >1 decade CO2 changes caused global scale
Little Ice Age Late 1500s Possibly global Causes: Volcanoes Anthropogenic activity
Effect of Volcanic Eruptions Ash
Cools Earth Increases albedo Stratospheric SO2 High altitude SO2 produces aerosol cloud Scatters and reflects solar radiation Cools Earth
Sunspot Activities Cooler temps on surface of sun More sunspots leads to Earth receiving more solar radiation Surrounded by plages (hotter-than-normal areas) Direct relationship between # sunspots and Earth's temp
Present-Day Heating of Earth Past 150 years El Nino Southern Oscillation (ENSO) Events Major shift in oceanic circulation Peru/Ecuador coasts Every 2 7 years, around Christmas ENSO causes most variability
La Nina and Southern Oscillation La Nina Part of Southern oscillation Opposite of El Nino More extreme version of "normal" circulation in tropical Pacific (Indonesia) Water colder than normal Southern Oscillation When pressures are low in the west, they're high in the east, and vice versa
Chapter 16: Global Warming Increased CO2 From 1800 to 2001, CO2 increased ~25% Causes: Fossil fuel burning Deforestation (to a lesser extent)
Natural Reservoirs and Fluxes of CO2
Fossil fuel reservoirs: coal, oil, natural gas Largest fluxes: Exchange between atmosphere and terrestrial biosphere Exchange between atmosphere and ocrean
Carbon Dioxide Sinks Gets rid of CO2 Main natural sinks: Oceans Plants and other organisms that remove CO2 from the atmosphere Dissolution of carbonate sediments on ocean floor Silicate weathering
Changes in Sea Level ~ half of the rise in sea level due to thermal expansion of surface ocean water Melting of mountain glaciars Melting of polar ice caps
Effects on Ecosystems Increased rates of plant growth C3 and C4 plants C3 weeds out of control Changes in speciation within forests Extinction Insects will expand to mid-latitude Diseases (i.e. malaria) Coral reef extinction Fishery disruption
Economic Consequences Decreased agricultural output Relocating cities Alternative energy costs