ESS205 – Confronting Global Change (1).pdf

ESS205 – Confronting Global Change Lecture 1: brief history of the Earth system Environmental science ● Tries to remain objective ● Can be applied in policy and management decisions environmentalism ● Social movement dedicated to protecting the natural world ● Aims at influencing policy The Earth...

ESS205 – Confronting Global Change Lecture 1: brief history of the Earth system Environmental science ● Tries to remain objective ● Can be applied in policy and management decisions environmentalism ● Social movement dedicated to protecting the natural world ● Aims at influencing policy The Earth system: Components: 1. Atmosphere (troposphere) 2. Biosphere 3. Geosphere 4. Hydrosphere *It is closed (matter cycles within system but energy is exchanged with space)* Atmosphere: ● Mixture of gasses ○ 78.084% (in dry state) Nitrogen (N2) ○ 20.947% Oxygen (O2) ○ 0.934% Argon (A) ○ 0.035% Carbon Dioxide (CO2) ● Water vapour (around 4%) ● 5 main layers ○ Based on temperature changes ○ Chemical composition ○ Movement ○ Density ○ Most of the molecules in the troposphere ● Weather in bottom Biosphere: ● All living organisms ○ Around 1.5 million species known Hydrosphere: ● Mostly saltwater (oceans) ● Much freshwater is frozen (cryosphere) ● Surface water is very small portion of total Geosphere: ● Rocks and sediments ● The lithosphere is the upper part of the solid earth which interacts with the other components The carbon cycle: ● Most life on earth is carbon-based ● Concept of residence time ○ Typically flow in = flow out ○ Residence time is average time this material stays in the component i.e. a water molecule spends in the reservoir ○ Calculates as: amount within component divided by flow in or out Earth system science: ● A global view of planet which integrates finding of physical and biological sciences ● Considers complex interconnected web of physical, chemical, and biological processes ● Discusses modification of these processes, and changes of these components through time ● Two sources of energy fuel the dynamic earth system ○ External ■ Solar radiation ● Drives hydrological cycle and ocean and weather circulation which cause erosion of the land surface ○ Internal ■ Radioactive decay and cooling of planet ● Drives volcanism and plate tectonics Global change: ● Modifications of earth system’s components and their interactions ● Both natural and human induced ● Can be gradual over long period (millions of years) or catastrophic (seconds to centuries) ● Can be unidirectional (evolution of life and atmosphere) or cyclic (supercontinents, glacial-interglacial) ● Is not a recent phenomenon ○ It is a characteristic aspect of the earth system ● How does it relate to humans? ○ human-induced change ■ Population growth → environmental impacts ■ Reached 8.1 billion in August 2023 ■ Due to technological and medical advances ■ Humans need energy and resources ○ Environment sets limits ■ Limited water, shelter, resources, predation, disease, waste products in environment ○ Growth rate may go to zero ■ # of deaths = # of births ■ Growth curve becomes S-shaped, logistic growth limit is carrying capacity Drivers of population change: ● Number of births drop, number of deaths increase and will become similar by the end of the century ● Life expectancy has risen ○ From 32 years in 1900 to 71 years in 2021 due to improved health ○ Overall reduction of health inequality Consequences of human-induced change: ● Loss of habits and biodiversity ● Deforestation ● Desertification ● Soil degradation and erosion ● Pollution of water and air ● Ozone hole ● Acid rain ● Enhanced greenhouse effect (CO2 to atmosphere and global warming) ● Ocean acidification Lecture 2: the geography The earth’s structure: Rheology — a property defining deformation and flow of matter ● Changes with temperature, pressure, water content composition strength/behavior Crust Silicate rock (Silicon and oxygen compound) E.g. feldspar KAISi3O8 Elastic; brittle mantle Silicate rock (but with more iron and magnesium) E.g. peridotite, (MgFe)2SiO4 Solid and creeping (a crystalline solid and also very slow solid-state flow) Core Mainly iron and nickel (outer core) fluid-like fast circulation and flow Lithosphere — plate boundaries: ● Plate boundaries are locations of geological activity ○ Volcanoes ○ Mountain belts ○ Earthquakes ○ Geothermal heating Types of plate boundaries: Divergent – move away Convergent – move towards Transform – slide past Continent split apart ● Rift valley ● Ocean Ocean-ocean ● Lithosphere being recycles subduction zone ○ Volcanoes ○ mountains Lithospheric plates sliding past one another E.g. San Andreas fault Ocean-continental New lithosphere being created: Continent-continent collision ● Create fold mountains Plate velocities: ● We can directly measure plate velocities ○ First with VLBI in the 1980s (very long baseline interferometry) ○ Now GPS ● Earth’s magnetism ○ The polarity of the earth’s magnetic field reverses every 500,000 years ■ This is recorded in the sea-floor: as new ocean is created it “locks it” a signal of the magnetic field (normal vs. reversed), yielding symmetric patterns of sea floor stripes Types of rocks: ● Igneous rocks ○ Magma → cools → igneous rock ○ Upper mantle is solid rock, magma forms under special circumstances at: ■ Subduction zones ■ Mid-ocean ridges ■ Hotspots ○ Magma composition determines mineral content ■ Felsic (feldspar, light colour) ■ Mafic (magnesium and iron, dark color) ○ How rapidly magma cools determines mineral size ■ Slow cooling → large crystals ■ Fast cooling → small crystals ○ Composition tells us where rock formed and style of eruption ■ Basalt ● Shield volcano ● Hot spot/MOR ● Lava flows ■ Andesite ● Composite volcano ● Subduction ● Explosive ● Sedimentary rocks ○ Process ■ Sediments → deposit → sedimentary rock ■ Dissolved ions → precipitate → sedimentary rock ■ Animal shells → settle → sedimentary rock ○ Types ■ Clastic sed. Rocks (sandstone, shale) ■ Evaporites (gypsum, rock salt) ■ Biogenic (limestone, chalk, coal) ○ Sedimentary rocks retain information on: ■ Transport mechanism (water, wind, ice) ■ Environment of deposition ● Metamorphic rocks ○ Original rock → pressure & temperature → metamorphic rock The rock cycle: ● Rocks continuously transform from one to another (on slow time scales) Soils: ● Weathering of rocks → regolith becomes soil because of influence of biosphere and atmosphere Lecture 3 – life and time on earth Uniformitariansim – geologic process operating at present are the same as those that operated in the past How to decipher earth/life history: ● Relative time ○ E.g. interpret that trilobites predated dinosaurs who predated humans ○ From understanding the rock formations ○ Sedimentary rocks are deposited in horizontal layers ■ Principle of original horizontality ○ Infer that young strata overlay older ■ Principle of stratigraphic superposition ○ Disrupted pattern is older than the cause of disruption ■ Principle of cross-cutting relationships ■ E.g. faults, magma injections Oldest to youngest: C > B > A > D >E ● Absolute ages ○ Based on radioactive decay of unstable isotopes ○ Since these materials are unstable and decay at very precise rates, we can use them as geological chronometers – geochronology A short history of earth: ● Earth was created 4.7 Ga (giga annum) of years ago ● Earth scientists use the following divisions ○ Eons ○ Eras ○ periods ● Divisions are agreed on by a certain feature (e.g. the appearance of a fossil) anZd described for a specific location Paleozoic (540-250 Ma) Cambrian explosion: ● At ~540 Ma, rapid appearance of complex life in fossil record ● Massive diversification of species (“big bang of ecology”) ● E.g. Gurgess shale, AB Hadean eon: (started 4,567 million years ago) ● Solar system forms from nebula ○ Contracts and spins → disc ○ Sun at center ○ Inner rocky planets (includes earth) ○ Outer gas giants ● Date of formation from radiometric dating of meteorites ● Lots of impact, including a huge one which formed the moon ● Magma ocean, water vapour, lots of impacts Middle Paleozoic: ● First land plants in Silurian ● Amphibians in Devonian ● First seed plants ● First forests ● First soil Mesozoic era: (250-65 Ma) ● Time of dinosaurs ● Emergence of dinosaurs in Triassio, also swimming and flying reptiles ● Mammals also develop in Triassio ● Bipedal movement ● Atlantic opens, first birds in Jurassic ● Gymnsperms, cycad trees K-T extinction event: ● At 65 Ma, almost vertebrates (in land, sea, air) become extinct; many invertebrates, land plants too ○ ~60% of species on planet dies out ● Probably an asteroid ~10km in diameter collides with Earth ● “Nuclear winter” atmospheric effect Evidence for Bolide Impact: ● Spike for iridium (extra-terrestrial element) at K-T boundary ● Chicxulub impact crater at Yucatan ● Massive tsunamis along Atlantic coasts at ~65 Ma Cenozoic (65 Ma to present) – time of the mammals The future: ● We can predict next supercontinent “Pangea Ultima” in 250 Myrs ● Earth will cease to exist in about 5 billion yrs ○ Sun will run out of fuel and briefly expand into a red giant ○ Earth will evaporate Lecture 4 — the hazardous earth Tectonic hazards – earthquakes ● Release of seismic energy at fault zones in the earth ○ Seismic events = acoustic events moving through the solid earth ■ E.g. an ultrasound – acoustic event through your body ● Definition ○ ground motion (shaking) resulting from a sudden release of acoustic energy in the lithosphere ○ Normally these occur along geological faults ■ Planar factures in the earth ■ Tectonic stress/energy builds up when faults are locked, and when these faults rupture or slip, seismic energy is released in the form of an earthquake ● Magnitude ○ A measure of the strength of an earthquake is the Richter scale ○ It is calculated by the amplitude of the seismic waves from an e/q ○ A logarithmic scale ■ Each number increase in magnitude means ○ We now use the moment magnitude scale ● Largest earthquakes ever recorded by humans ○ 1960 - 9.5 - Chile - subduction zone ○ 1964 - 9.2 - Alaska ○ 2004 - 9.1 - Sumatra ● ● ● ● ○ 2011 - 9.1 - Japan ○ 1952 - 9.0 - Kamchatka ○ 1906 - 8.8 - Ecuador ○ 2010 - 8.8 - Chile Case study - 2023 Turkle events ○ At 4:17AM february 6, a M7.8 earthquake occurred in SE Turklye ○ Followed by a M7.5 event nearby at 1:24pm that same dat ○ Rupture along the east Anatolian Fault ○ Over 67,000 people lost their lives in Turkiye and Syria ■ Mainly from collapsing buildings Seismic hazards of Southern Ontario ○ Southern Ontario has some earthquake activity, but this is low magnitude ○ But its not on a tectonic boundary, so what causes these earthquakes? ■ Usually occur along pre-existing structural faults (ancient suture zones and upper crustal features) ○ Dresses may be due to glacial isostatic adjustment or perhaps just to background intraplate stresses Local geology shows near-surface structures in glacial units Can we predict earthquakes? ○ Tsunami hazards: ● How it is caused ○ Series of ocean waves created when seafloor is rapidly displaces ■ E.g. by an undersea earthquake ■ Could also be triggered by undersea landslide, asteroid impact ○ From Japense: (tsu) habor (nami)wave ○ Even a small displacement of the seafloor causes a tsunami (just 10m vertical fault motion displacement can induce a massive tsunami) ○ A major earthquake with modest (10’s m) vertical fault rupture causes uplift of several km of a water column above (the normal ocean is ~4km deep) ■ This is a huge amount of energy transferred to ocean (e.g. compared to wind perturbation of water) ● In deep ocean, the wave perturbation has: ○ Small amplitude (height) ○ Long wavelength (width) ○ High speed: ● As tsunami approaches shore: ○ Amplitude increases ○ Wavelength decreases ○ Speed decreases ● Case study: 2004 Sumatra-Andaman tsunami ○ December 26th, 2004, a M9.2 earthquake occurred off the coast of Sumatra at 30km depth ○ Seafloor crustal rupture along 1600km and several metres ■ This displaces ~30km^3 of ocean water to produce the tsunmai ○ Tsunami wave front rockets around Indian Ocean ○ Waves up to 30m high across Indian Ocean >227,000 people die from the tsnami ● Detection ○ Detection systems have been deployed ■ E.g. using bottom pressure detectors and communication buoys ○ DART: deep-ocean assessment and reporting of Tsunami ■ This is a warning system (not prediction) Natural hazards of the planet: ● Tectonic ○ Volcanoes ○ Earthquakes ○ Tsunamis ● Weather ○ Storms ○ hurricanes/typhoons ○ Tornados ○ Floods ○ Wild fires ● Extra-terrestrial ○ Meteorites ○ Solar storms ● Geological ○ Mass wasting Lecture 5: resources from our changing planet Populationa and resources: People overpopulation ● Too many people living in a given geographic area Consumption overpopulation ● Each individual consumes too large a share of resources *both lead to increased use of resources and destruction of environment* ● 25% of humans consume ○ 50% energy ○ 86% aluminum ○ 76% harvested timber ○ 61% meat ○ 42% fresh water ● 75% of pollution and waste Resources: ● Non-renewable ○ Limited supply, do not regnereate (or very, very slowly) ○ Fossil fuels ■ Millions of years oto accumulate oil, gas, coal ○ Nuclear fuel ■ Safety and waste a concern ○ Minerals ■ Metals: iron, aluminum ■ Industrial: gravel, sand ■ Critical: lithium, nickel, cobalt ○ Environmental impacts of mining ○ Our consumption of these non-renewable materials is changing the earth ● Renewable resources ○ Virtually unlimited, replenish over short time period (e.g. forests, fisheries, groundwater, agricultural land and soil) ○ Easy to overexploit ■ E.g. fish stocks → used in a non-renewable way ○ Renewable energy ■ Hydropower → environmental impacts ■ Solar → expensive ■ Wind → unpredictable ■ Geothermal → limited locales (for electricity) Minerals and mining: ● The importance of mining for Canada ○ $97 B (6% of Canada’s GDP is directly linked to mining Canadian mining assets totalled $273 B in 2020 (of this 69% were located abroad) ○ Canadian companies in 2021 spent $3.6 B on exploration and appraisal ● “Critical minerals” ○ Important for green/digital economy and security ● Primary (in host rock) vs secondary (after moving) mineral deposits ○ Primary ■ Hydrothermal ore deposit and gold vein (industrail: open pit or underground) ○ Secondary ■ Placer deposits and gold nugget (artesinal: panning or dredging) ○ *these determine the type of exploration, extraction, and production required* ● Mineral resources cycle ○ Largest underground salt mine: Goderich, Ontario ○ Largest open pit mine: Bingham Canyon Mine, Utah, 1,2 km deep, 4km wide ○ “Monte Kali” near Heringen, Germany 100m high, mining of potash for over 125 yrs, 200M tons of salt, 14,000 tons/day added ● Mine tailings – wastes that comes from mining ○ Gold ■ Ore typically contains 1g/ton ■ Ore is crushed ■ Gold may be removed from rock by acid leaching or now more ○ Oil sands ■ Bitumen is removed from sand using hot water ● Acid rock drainage – leaching of metals, weathering of exposed sulfides creates sulfuric acid ○ E.g. Britannia Mine, BC ■ Operating from the 1880s, was largest copper mine in British Empire in the 1920s ■ Local groundwater and surface water polluted by sulphuric acid and dissolved metals from the mning ○ WQC = water quality criteria ● Reclamation ○ Return land to end use (habitat, agriculture, development) Case study: Efemcukuru gold mine ● A “sustainable” mining operation in western Turkiye near Izmir ● Partly owned by Eldorado Gold, a Canadian company ● Vein ore deposit requires underground mining to follow the deposit to depth ● In lifetime of operation it is estimated that 8.5 million tons of ore will be mined ● Estimated mine life of 7 years (a relatively short time…) ● conservation/reclamation ○ Backfill excavation ○ Filtered waste water mised with cement for backfill ○ Slope stabilization and site rehabilitation with olive groves What is gold? ● Native chemical element Au ● Dence, soft, malleable, ductile ● Very non-reactive chemically ● Used in jewelry, electrical connectors, IR shielding, teeth ● Mainly used as a common financial standard ● Alloyed with other metals to strengthen Au ● “Karat” unit measures purity ○ 24kt gold is pure (100%) gold ○ 18 kt gold is approx 75% gold Diamonds: ● A natural mineral ● Solid form of carbon © with atoms in cubic diamond crustla structure ● Hardest know natural material (hardness 10 on Moh scale) Diamonds created beneath the lithosphere (high pressure: 4-6 GPa; 150-200km beneath the surface) Brought to the surface in kimberlite pipes Volcanic ultramafic magma from mantel possibly containing diamond xenoliths A properly cut diamond takes into account the internal reflection of light in the diamond An ideal cut internally reflects the light back out to make a more brilliant diamond Color is influenced by chemical or structural impurities in diamond Huge variation in colour, although some are especially rare Clarity: ● Flaws in diamonds can result from inclusions fractures (during cutting, etc) ● Most natural diamonds have inclusions, hence the flawless diamonds have most value ● The inclusions can give us interesting scientific information on the age/conditions in the earth’s mantle Production in Canada: ● Most diamonds in canada are mined in the NWT ○ E.g. Diavik mine starts producing in 1998 ● Part of kimberlite filed archean in the slave province (a geological unit) The challenge: ● The operation ○ ~2.8 carats per ton of ore ○ ~reserves of 52.8 million carats ○ Employing 1000 people onsite for 25-30 years lifespan of the mine ○ Close connections and involvement with local indigenous groups ○ “Ethically and sustainably” sourced diamonds Lecture 6: fossil fuels and our changing planet Fossil fuels: ● A hydrocarbon-containing material of biological origin, sourced in the solid earth, that can be source of energy ○ May include such material as coal, petroleum, natural gas, oil sand and heavy oils ○ Fossil fuels may be burned to produce energy, but this reaction releases CO2 into the atmosphere ○ >80% of primary energy production by humans is through fossil fuels ○ Petroleum may be refined into other products such as plastics, textiles, paints, fertilizers ● Hydrocarbons ○ Dead organic matter from plants and animals ○ Energy originally from the sun stored in organic carbon ○ Under the right pressure and temperature, will form some type of hydrocarbon ○ Deposited and trapped in the Earth’s crust ● Future ○ Oil ■ 33% of current energy use, 22 billion barrels per year current reserves > 1,000 billion barrels estimate undiscovered 500 billion barrels consumption projected to increase ○ Coal ■ 30% of energy use, abundant current reserves > 800 gigatons (equivalent to 4,500 billion barrels of oil) ■ Expansion has been growing ■ Contains impurities (sulfur, mercury, arsenic) ● Depends on how it is formed (e.g. eastern canada high in sulfur because formed in ocean) ○ Gas ■ 24% of energy use ■ Current reserves 180 trillion cubic meters (equivalent to 1,000 billion barrels) Extracting petroleum: ● Production types ○ Pumping ○ Steam injection ○ Strip mining ■ E.g. Alberta tar sands ● Petroleum or “crude oil” is a liquid that can be pumped out of the ground ● Human causes of increasing earthquake events ○ Fracking / hydraulic fracturing ■ A method used to extract natural gas and oil from deep underground ● Usually in a rock type called shale that holds the hydrocarbons more closely ● Process involves injecting large amounts of water, sand, and chemicals into a wellbore ● The injected fluid helps to prop open the fractures, while the sand acts as a proppant to keep the fractures from closing when the pressure is released ● These fractures allow the trapped gas or oil to flow more freely and be extracted ■ Environmental concern: impact on groundwater ● Migration of fracking fluid directly into groundwater ● Flowback of contaminated wastewater at the surface ● Methane leaks into groundwater ■ Fracking also induces seismicity ● Injection of fracking fluids into the ground can change the stress field around the fractured layers ● This can cause slip/motion on the fractures → release of acoustic energy as a small earthquake ● In most cases, magnitudes are in the range M1-M3 ● E.g. fracking induced major events: M4.7 in NW BC in 2015; M4.0 in texas in 2018; M5.7 in China in 2017 What does combustion of petroleum mean for the Earth system: ● The issue in global change is whether humans significantly disturbing Earth’s carbon cycle ○ I.e. combustion of fossil fuels moves carbon (in the form of carbon dioxide) to the atmosphere ○ Cars are just one source of emission of greenhouse gases that are influencing the planet’s climate ● Commercial gas ○ 87 octane is approximately 87% octane and 13% heptane ○ 92 octane is approximately 92% and 8% heptane ● Ideal combustion of pure octane ○ 2C8H18 + 25O2 → 16CO2 +18H2O ● Realistic combustion ○ Fuel + air (N, O2) → unburned HC’s + NxO + SOx + CO + H2O + CO2 Lecture 7: Climate Factors that affect climate change: ● Atmosphere ○ Greenhouse gases ● Biosphere ○ Photosynthesis and respiration ○ Oceanic biological pump ● Hydrosphere (and cryosphere) ○ Ocean circulation ○ Reflectivity (albedo) ● Geosphere ○ Tectonics ○ Catastrophic events (volcanism, meteorites) ● Changes in solar radiation ○ Sunspots ○ Earth’s orbit Climate forcing – drivers of climate: ● Greenhouse gases ○ CO2, methane, nitrous oxide ■ Burning of fossil fuels have increased these re-radiate heat in atmosphere, cause surface warming ● Aerosols ○ Dust, smoke, soot, sulfates ○ Burning of coal, volcanicn eruptions ○ Net effect is cooling Climate feedbacks – amplify or reduce effects of forcing: ● Positive = amplifying ● Negative = stabilizing ● Clouds ○ Reflect ~⅓ of incoming sunlight ● Precipitation ○ Warmer atmosphere → increased precipitation ○ But some regions drier ○ Effect on planet growth ● Forests ○ Trees remove CO2 from atmosphere (carbon sink) ● Ice albedo ○ Warmer → less ice ● Water vapour ○ Most abundant greenhouse gas ○ Warmer atmosphere → more water vapor Climate tipping point — abrupt shifts, irreversible: ● Ocean circulation ○ E.g. slowing of gulf stream → cooling in europe, but warming in North America ● Ice loss ○ Ice reflects light, land surface absorbs heat ○ Less ice → runaway heating ● Rapid release of methane ○ Thawing of permafrost will release methane ● Tipping points are not independent of one another! Other influences on climate: ● Oceanic biological pump ○ Photosynthesis uses CO2 + more dust during glacial period ■ → more nutrients ■ → stronger biological pump ■ → drawdown of CO2 ■ → further cooling Peatlands: carbon storage Evidence for warming climate: ● CO2 increase ● Temperature increase ● Sea-surface temperature increase ● Sea-level rise (1997-2023: 97mm) ● Loss of sea ice and ice sheets ● Retreat of glaciers ● More weather-realted disasters Effects of Canada: ● Snow fall will increase ● Erosion ○ Loss of sea ice causes more wave action at shor ● Ice roads ○ Costly all-weather roads may need to be built to support mines and communities ● Fire — wldfires below the tree line ○ Threaten infrastructure, remote microwave towers ● Melting permafrost — threaten structures ○ E.g. roads, runways, pipelines, fuel storage Climate engineering: ● Adjusting climate by ○ Increasing albedo ○ Removing CO2 Intergovernmental panel on climate change (IPCC) report 2023: ● IPCC established in 1988 by the UN ● Provides assessments and recommendations about climate change to policy makers ● Sixth report completed in march 2023 ● The graph summarizes: ○ The cenozoic climate ○ The recent ice ages ○ The human induced change ○ Predictions for the future climate Lecture 8: climate change through earth history Key terms: Weather — state of the atmosphere over a short time Climate — weather averaged over a long period of time (>30 years) Global warming — the rise in global temperatures due mainly to the increasing concentrations of greenhouse gases in the atmosphere Climate change — encompasses all types of changes in the atmospheric climate that ccan be and have been observed from regional to global scales Receding glaciers: ● Both continental glaciers (Greenland, Antarctica) and alpine glaciers ○ E.g. Franz Josef glacier, South Island of New Zealand ● Last glacial maximum: ○ Cold period in earth’s climate from ~26,000-20,000 years ago ○ Maximum extent of recent glaciations ○ Global temperature about 6 degrees C lower than today ● Laurentide ice sheet ○ Covers most of Canad at LGM ○ Primary feature of Pleistocene epoch ○ Up to 3km thick at its maximum; several km’s covers the GTA ● Ice cores ○ By measuring oxygen isotopes in glacial ice cores, scientists can reconstruct global temperature trends – paleo climate ■ E.g. ice corres from Antartica and Greenland can have ice as old as 100,000’s years ○ Interpretation from Paleo climate data: ■ Warming and cooling cycles on earth ■ Ranges between about 10 degrees ■ Even the CO2 level in atmosphere is changing a lot ■ The climate excursions seem to be repeating (periodic) ■ The period of the main signal seems to be about every 100,000 years ■ Time scale: humans were around but not doing much ● Main causes ○ Most energy into the earth’s climate system is from the sun ○ In early 20th century, geophysicist Milutin Milankovitch suggested that glaciers advance and retreat through changes in earth’s orbital motions – since termed the “Milankovitch cycles” ○ Eccentricity ■ Measure the departure of the earth’s orbital ellipse around the sun from circulartiy ■ A more eccentric orbit = more seasonal variation ○ Obliquity ■ The angle of the earth’s axial tilt with respect to the orbital plane ■ Current tilt of 23.44 degrees is halfway between maximum and minimum tilt ■ Increased tilt generally = more extreme seasonal variations ○ Precession ■ The trend in the direction of the earth’s axis of rotation relative to a fixed distant point ● E.g. during northern hemisphere winter, we are currently at the closet point to the sun in the earth’s elliptical orbit ■ When earth precesses away, this will make for a colder winter (glacial) ■ Cyclical variations in earth’s orbit ○ Cyclical variations in Earth’s orbit ■ These variations change how much energy Earth receives from the sun ■ Put all these together, and we get the periodic variations in global temperature that seem to correspond roughly to the ice core data ■ So the earth itself is spinning itself in and out of these glacial/interglacial cooling/warming periods The disappearance of the Mediterranean sea: ● From about 5.9-5.3 myr ago, the mediterranean sea entirely dried up ○ Called the Messinian salinity crisis ○ The sea closed off from the Atlantic and evaporated over ~1000 years ○ Probably due to tectonics and a warm/dry climate ○ Strait of Gibraltar opened up again at 5.3 Ma ○ Zanclean flood Paleocene-Ecoene thermal maximum: ● Approx. 55 Ma, there was a hothouse Earth ● Global temperature rose by 5-8 degrees ● hot/wet climate dominated the entire planet, evven the arctic regions ● Probably caused by enhanced CO2 degassing of planetary interior by volcanism ● Eventually planet recovered with enhanced biological activity: moving carbon from atmosphere to ocean floor Snowball Earth: ● Its been proposed that Earth has gone through periods where entire planetary surface is frozen or galciated ● Most notably in the Neoproterozoic (about 650 Ma) ● Evidence is glacial deposits at this age occurring globally, and even at equatorial paleolatitudes ● Most of the earth’s surface energy comes from the sun ○ As more heat is immediately reflected, earth’s surface and atmosphere become cooler ○ A measure of how radiation is reflected from the surface of a body is called albedo ○ When snow falls on land or ice forms at sea, increase in albedo causes increased cooling which stabilizes snow and ice — ice-albedo feedback ○ As ice forms at lower and lower latitudes on earth, planetary albedo rises at a faster and faster rate (since surface area increases towards equator) ■ Ice-albedo feedback causes runaway freezing → a snowball earth ● How did earth get out of the snowball? ○ No carbon sink from atmosphere to surface ocean (no precipitation and weathering) ○ However, plate tectonics continues beneath the ice, and volcanism spews CO2 to the atmosphere: warming the planet Lecture 9: The Anthropocene The anthropocene — a geological epoch where humans are the dominant influence on Earth’s climate and environment Effects humans have had on the earth system: 1. Climate forcing from greenhouse gas emissions ● The “hockey stick” graph ○ “Increase in atmospheric carbon dioxide over the past 60 years is about 100 times faster than previous natural increases” ● Current global warming is happening much faster than it did compared to the warming interglacial events over the past million years ○ Humans could witness a warming of 4 degrees C over 110 years; normally this warming would take 5000 years according to climate controls ○ Greenhouse gas concentration left natural trend about 8,000 years ago (time of onset of cattle and wet rice farming) ○ Warming may have started ~15,000 yrs ago 2. Ocean acidification and heating ● “The ocean has absorbed enough carbon dioxide to lower its pH by 0.1 units a 30% increase in acidity 3. Current extinction ● Although extinction is a natural phenomenon, it occurs at a natural ‘background’ rate of about one to five species per year ● Losing species ~1,000 times the background rate 4. Garbage and plastic in oceans ● Pollution of groundwater and surface waters 5. Engineering and agriculture ● Agriculture and excavations shape the landscape more than rivers and glaciers How geologists may define the “Anthropocene”: ● Geological boundaries ratified based on one specific location GSSP (global stratotype section and point = “golden spike”) ○ 65 ratified, most based on fossils Arguments for defining the Anthropocene as a new geological period ● Philosophical arguments ○ Human history v.s. Geologic history ○ Uniting different disciplines ○ Irreversibility: loss of biodiversity, climate stability ● Ethical arguments ○ Societal context for geosciences ○ Difficult situation for geoscientists if this new division would be rejected ● Paradigm shift ○ Stratigraphy linked with huma history ■ Still, stratigraphic determination of ‘Anthropocene’ requires something unique in the sedimentary record ■ Likely candidate: Plutonium 239 from above-ground nuclear tests starting in 1952 (detectable world-wide)