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Earth Sciences
Earth Sciences 2240F/G
Jennifer Mac Rae

Earth Science Final Exam Notes Lawrence Wengle Weather: Short term state of the atmosphere with respect to temperature, moisture, wind velocity and barometric pressure Climate: Average long-term weather conditions for a region, including things like average temperature and precipitation  Both have energy supplied by Sun Greenhouse Effect: controls warmth of bodies of water and climate, degree of reflecting infrared radiation back to Earth – Carbon Dioxide, Methane  Presence of CO2 on Venus suggests climate was once the same Energy from impacts: Earth is impacted by 100-1000 tonnes of dust every day  Meteoroid impacts cause massive energy releases, even if small CHAPTER 10 Atmosphere: composed of multiple layers all with their own physical and chemical properties. Consists of 4 layers: 1. Troposphere – surface level to 12km (80% of atmosphere thickest at equator, thinnest at poles), main layer of atmospheric circulation (Tropopause) – equal pressure marked by jet streams 2. Stratosphere – up to 50km – zone above weather, ozone enriched 3. Mesosphere – up to 80km – asteroids begin to burn, lack of ozone 4. Thermosphere – up to 500-700km (ionosphere) – air thin and responsive to solar radiation, dramatic temperature changes Mars, Earth, Venus originally had almost identical atmosphere compositions o Venus: CO2 filled atmosphere, greenhouse very strong, equilibrium reached at very high temperature 737 K o Mars: smaller planet that cooled more quickly, less internal heat, surface dropped, from the water the hydrogen escaped (mars low escape velocity) and oxygen combined in surface soils (red colour). The atmosphere is thin today and surface temperatures fluctuate. Dynamics of the Atmosphere o When a compound changes state, energy is either absorbed (ice to liquid) or released (liquid to ice) in the process o Amount of energy released or absorbed per gram of matter during a change of state is known as latent heat (2260Joules/gram or 540 calories/gram) o Air moves in convection cells in troposphere in response to: o Temperature gradients o Density gradients o Pressure gradients o Density = Mass/Volume The density of air decreases when heated, density increased when increasing pressure o Density at lowest: at high elevation, hot day, low pressure o Density at highest – low elevation, low temperature, high pressure o Adiabatic processes – occur without addition or subtraction of heat from any external source (no heat involved) o Parcels of air heated near earth‟s surface, air pocket expands when heated, becomes less dense and rises to a point of lower pressure at high altitude. The rising parcel of air then cools and its density will slowly increase to match surrounding air and stops rising – no water in this air o Humid air is lighter/less dense than dry air – so evaporation adding water to the air causes a decrease in air density, which can rise to higher elevations. Here the humid air also is heated, rises, expands, and once it cools condensation begins – which releases latent heat Convection and Rotation o Earth‟s surface heated unevenly – more of suns heat is received per unit of land surface near equator than near the poles – uneven heating gives rise to convection currents o Coriolis Effect – effects of rotation on atmosphere o Breaks up the flow of air between the equator and the poles into belts o Hadley cells, ferrel cells, polar cells o Air movement associated with boundaries lead to formation of polar jet stream/subtropical jet stream  Aid in development and direction of storms  Jet stream winds must exceed 57Km/h Wind  The movement of air from high-pressure zone to a lower pressure zone o Wind is effected by the Coriolis force – deflected to right in northern hemisphere and left in southern hemisphere) o Winds around low pressure centre develop inward spiral motion o Winds around high pressure centre develop outward spiral motion o Isobars – show how strong/weak wind is – the more and closer together the stronger the winds o Very close isobars signify spiral patterns of cyclones and anticyclones o Cyclones – strong spiral patterns around low pressure cells  Inward spiral flow leads to upward flow of air at centre, moist air flows upward to produce clouds and rain o Anticyclones - strong spiral patterns around high pressure cells  Outward spiral flow is called divergence, air flows out at base, cold air drawn downward compressed and heated adiabatically leading to clear skies Oceans 2 circulation systems in oceans – wind driven (surface circulation) and density driven (deep water) Ocean Current Flow – expressed in million of cubic meters per second Salinity – density of seawater – grams of dissolved solids per kilogram of seawater o What's really measured is the water‟s electrical conductivity, which is directly proportional to the amount of dissolved solids in water North Atlantic warmest and most saline – mean potential temp of 5.08C and 35.09 salinity 77% of worlds oceans colder than 4 C, surface 26% colder than 4 C o Cold water sinks Surface Waters o Most of surface circulation is driven by winds – results in huge gyres of water at subtropical altitudes o Gyres – 5 worldwide, wind driven o Blowing wind interacts with upper layer of ocean and sets it in motion in same direction as the wind (surface flow to right in n.hemisphere and left in s.hemisphere) o Top layer of water pushed/drags the layers below, which are deflected a littler further right or left than the surface layer and are slowed by friction – this process continues down into the water column to depth of 100m, creating downward spiral of water gradually deflecting further and further the right/left o Winds blowing toward southwest push waters northwest, mid latitude winds blowing northeast push surface waters southeast o Together these two winds drive the uppermost layer of water into the centres of the subtropical gyres and pile up a lens of warm water o Seawater in the centre of the lens sits 2 meters higher than the rest of the ocean, water flowing away from the lens is turned to the right by the Coriolis effect, creating a huge subtropical gyre spinning in a clockwise direction (counterclockwise in southern hemisphere) o This is transportation toward the equator, cold water from poles moving to equator o In Northern Atlantic transport toward poles occurs in Gulf Stream, warm salty water headed north o Warm northward moving conveyor belt transfers lots of heat to the atmosphere – transfer of warm North Atlantic water to the cold overlying air is about equal to the amount of solar radiation received in the same region Deep ocean circulation – density driven Thermocline – zone of rapid temperature change between warm upper layers and cold water filling the deeper ocean basins (El Nino) 1. Deeper permanent portion maintained throughout year 2. Shallower portion that changes as a result of seasonal heating Poleward flow of warm water occurs above the thermocline – called thermohaline flow (halite meaning salt) Waters form and sink because they are denser than the underlying water o Sea water 3.5% more dense than freshwater o Density can be increased at low latitudes when atmosphere evaporates water, leaving the remaining water saltier (i.e. more dense) and by formation of sea ice that stores freshwater and leaves salt behind o Density also increased if ocean is cooled – salt loses weight and gains density when cooled by the atmosphere Deep water formation in North Atlantic Deep Water region and Antarctic Bottom Water – all this water is sinking because it is dense – water must then come back toward surface through process called „upwelling‟, aided by surface winds and the Coriolis effect. CHAPTER 11 Thunderstorms 3 requirements: 1. Moisture – supplied by large bodies of water 2. Atmospheric instability – unstable air mass has warm moist air near surface below cold dry air above it – if a parcel is forced upward it will continue to rise on its own 3. A lifting mechanism – needs something to initiate upward motion o Differentiation – warmest air above surface, thermals, tend to rise o Cold fronts – boundary b/w two air masses of different temperatures, fronts lift moist air, lifting cold air the most abruptly, if air is moist and unstable, thunderstorms will form along the cold front o Mountains/terrain – air forced up the slope of rocks, upslope thunderstorms in Rocky Mountains in summer are common Lifespan o Thunderstorm cell has a distinct lifespan that lasts about 30 mins 1. Towering cumulus stage – cumulus cloud grows vertically, possibly 6km, air within cloud dominated by updraft, some turbulent eddies around edges 2. Mature stage – 12 to 18km, updrafts/downdrafts coexist – most dangerous stage as updrafts can be very strong 3. Dissipation stage – downdraft cuts off updraft, no more supply of warm moist air to maintain itself so it dissipates. Light rain and weak outflow winds may remain before leaving behind an anvil-shaped top Types of Thunderstorms o Single cell – very rare o Multi-cell – most storms form in clusters – cells merge together, can last for several hours producing hail, damaging winds, floods, tornadoes o Squall Lines – storm formed in line and extends laterally for many miles, most extreme are called “derecho” o Supercells – cells unite producing one massive rotating thunderstorm, responsible for most tornadoes and major hailstorms, sometimes cause wall clouds that extend down to start tornado o Thunderstorms cause lightening, hail, strong winds Tornadoes Tornadoes are the smallest most violent weather disturbances on Earth, defined as a rotating column of air (counterclockwise in N. hemisphere) descending from a thunderstorm and in contact with the ground – usually brief but can sometimes last over an hour and travel several kilometers causing considerable damage o 1000 tornadoes in US per year, peak season is April-June o Most tornadoes come from supercell thunderstorms o Vertical tube rotating rapidly (walls are moisture), established internal vacuum o Descending funnel surrounded by water droplets that give it shape, picks up debris and gets wider o In the centnd the vortex is open and air is clear (similar to hurricane) o Canada 2 to US in tornadoes, most in southern Ontario late spring early summer Fujita Scale: Category (MPH) Damage F-0 Gale (40-72) Signs, chimneys, branches broken F-1 Moderate (73-112) Roofs peeling, mobile homes pushed F-2 Significant (113-157) Roofs torn off, mobile homes demolished F-3 Severe (158-206) Roofs/walls torn off, trained overturned, trees uprooted F-4 Devastating (207-260) Houses leveled, cars thrown F-5 Incredible (261-318) Houses thrown, cars thrown hundreds of yards Hurricanes Hurricane 1. Severe tropical storm in North Atlantic Basin 2. Originates within the belt of tropical trade winds, roughly 5-20 degrees from equator 3. Rotates counterclockwise around an „eye‟ with minimum speed of 119km/h o Formed in North Atlantic Ocean, Northeast Pacific, or South Pacific o Need warm tropical oceans, light winds above them o Can produce violent winds, waves, floods and rain Different names: Typhoon – Northwest Pacific Ocean west of dateline Severe Tropical Cyclone Severe Cyclonic storm Tropical Cyclone Atlantic Hurricane Season June 1-Nov 30, 6 per year East Pacific hurricane season May 15-Nov 30, 9 per year Storm Surge – heavy waves that can damage buildings, cars etc., very dangerous and the reason why you must stay away from the Ocean during a hurricane o Governments allow too many people to live in risky areas near the coast Tropical cyclones, hurricanes, typhoons o Slowly advancing or stationary cold front develops a bulge, at the boundary where cool and warm air meet travelling in opposite directions o As moving air deflects, the bulge grows, forming a warm rightward moving front on the right side, and a cool leftward moving front to the left side of the bulge o Since cold air is denser, it moves faster than the slower warm front o As the faster moving cold air catches up with the slower warm air, the cold air under-rides the warm air, lifting a cell upward o This lift produces a low pressure area at the point where the two fronts interact, the lifted air expands, cools adiabatically and condenses over the low pressure zone o When the cold has taken over the warm front, occlusion is formed o Occluded front – lifted completely off the ground into the atmosphere o Disturbance is now a fully developed cyclonic storm, with low pressure centre, moving generally with easterly winds Origin of Hurricanes o Hurricanes (northern hemisphere) begin with a disturbance in the westward-flowing air not far from the equator o Sea surface temperature must be 26 or higher (implication of global warming) o As water vapour rises, it condenses which releases a large amount of latent heat energy – release of latent heat in transformation from gas to liquid o This is the main energy source of hurricanes o Avg hurricane releases 8000x more latent heat than electrical power generated each day by the US o Hurricanes are fueled by warm ocean water so it loses power as it crosses land, but can regenerate if it gets over the ocean again o First thing is a tropical wave, disorganized and characterized by masses of thunderstorms o Next is a tropical storm and a name is given o Difference b/w tropical storm and hurricane is just wind velocity Structure o Hurricanes have series of rain bands, spiral bands of torrential rain surrounding the eye travelling at hurricane wind velocity o The entire storm is also moving at speed called storm-centre velocity o Slowest in tropical regions o Destruction of hurricanes always greater on the right side Effects on Ocean o Sea swells – smooth long period waved that move out in all directions from the storm centre, can be 6-12 hours ahead of the eye o When the hurricane moved to land, the mound of water gathering at the eye also moves inland causing most deaths and destruction from hurricanes in this surge Hurricane Intensity o Measured by numbered categories on the Saffir-Simpson Hurricane Scale o Wind velocity, height of sea rise, and extent of destruction used in scale o 2 does 4x damage of 1, 3 does 40x the damage, 4 120x, 5 240x the damage of a 1 o (Scale) o Several category 1s occur many times yearly, while a category 5 occurs once in several years Example: Hurricane Andrew (1992) o Category 4 in Miami, almost went right through city o Crossed Florida and lost power, but continued, caused $25 billion in damages, but only 50 deaths o “Spin-up vortices” produce hurricanes most powerful winds but small area, can be double the speed of rotation of the main vortex Katrina (2005) o Costliest, one of deadliest hurrithnes in American history o Category 5, second of 2005, 6 strongest Atlantic hurricane ever o Locks were breached, flooded 80% of New Orleans o $75 billion in damages, costliest in US history, killed over 1600 Storm Prediction o No atmospheric conditions measurable that can predict where a hurricane will develop (thunderstorms can be predicted) o But satellites can spot the development of hurricanes and can follow them o Correlation between West African rainfall and hurricanes – the more rainfall produces more vegetation and enhanced evapotranspiration from plants (water added to air from plants) decreasing air density, thus more upward air convection over Western Africa. That interferes with the eastern airflow moving across Western Africa into the Atlantic, favouring hurricane development o Wet/dry periods in Africa also correlate well with increases and decreases in US hurricane exposure o Currently in dry period low exposure to hurricanes past 25 years so low hurricane awareness to people living on southeast coast, meaning if a wet period begins with increased frequency and intensity, likely to be enormous loss of life and property o As atmosphere warms so does the surface of the ocean, leads to increase in evaporation rates and rapid convection leads to increased latent heat energy from condensation at the dew point elevation, and this latent heat energy is the driving force of storms, warmer oceans provide more energy to develop more frequent and intense hurricanes, and more northward storms Names o Once known by date and place o 2 name lists developed for Pacific Basin and Atlantic Basin o 6 separate sets of each basin, sets repeat every 6 years o Very destructive storm names go to Hurricane hall of fame and are retired (Andrew 1992, Mitch 1998) o Not enough names, assigned Greek letters Stormfury - seeding o US effort to seed hurricanes and measure resulting modifications because even a small decrease in a hurricanes energy would be worthwhile o Adding silver iodide or dry ice to hurricane by means of an airplane o Purpose is to produce ice crystals from the super-cooled water in the hurricane walls o Believe that growth of ice from water would release some of the latent heat energy in the wall of the eye, if seeded properly it would widen the eye spreading energy out over more area, thus decreasing its velocity o Hurricane Debbie seeded successfully in 1969 o Seeding ended, not legit Frequency of Atlantic Basin Hurricanes o Every year is different, 8 in 1999, but only 4 in 2002 o 15 in 2005, 4 of them at category-5 o Likely to occur again as earth and oceans warm CHAPTER 12 Climate: Average long-term weather conditions for a region, including things like average temperature and precipitation Climate of Earth has changed over time, 21,000 years ago ice covered Canada and Europe and sea levels were over 100m lower than today. 100 million years ago there was no ice and sea levels were very high To consider substantive change, need to look at geologic time which has been around for hundred of millions of years. o Earth formed at 4.54 billion years ago o Use linear and log scales Climate System o Forcing – factors what cause climate changes o Response – variation in climate produced by forcing event 3 causes of climate change – forcing factors 1. Plate tectonics – internal heat engine, ocean circulation/currents based on arrangement of continents 2. Earth’s orbit – Milankovitch‟s 3 factors of orbital variation a. Orbit varies in periods lasting over 100,000 years, sometimes orbit is circular sometimes its more elliptical – can vary Earth‟s solar radiation by as much as 10% each period b. Tilt changes from 21.5 to 24.5 in pattern over 41,000 years, lower tilt gives less radiation in summer more in winter, smaller tilt means greater contrast between summer and winter c. Wobble of axis by gravitational pull of Sun and Moon changed equatorial bulge, changing direction of tilt, 26,000 year cycle 3. Sun’s energy – strength of sun has increased slowly throughout history, and sunspots result in variations in radiation arriving to Earth Climate system response o Quick changes give little time for response, more gradual changes are responded by the climate system o Equilibrium is difficult to achieve 1. Rate of response of the system is fastest when climate system is farthest from the equilibrium it seeks 2. The system has many components with different response times; each responds to the same forcing at its own tempo Climate system feedbacks o Positive feedback: Some factors already in climate system may amplify the forcing o Ex. If there were a decrease in Sun‟s energy to heat earth, it would result in more ice and snow cover on land. This snow would reflect sunlight decreasing the amount of heat received by Earth, further cooling the climate. o Negative feedback: factors suppress the primary forcing o Ex. Reflection of energy on warming of the atmospheric greenhouse that increasing CO2 content might be producing. Amount of incoming sunlight and amounts reflected and absorbed radiation depends on latitude. Albedo is the percentage of incoming radiation that is reflected rather than absorbed by a surface o Snow and ice have high albedos ranging from 60-90% o Albedo also vary depending on the angle the incoming solar radiation arrives o Type of vegetation covering land can affect average albedo o Vegetation-albedo feedback is when solar radiation is reflected leading to less absorbed heat and further cooling of the climate Climate Data Archives o Historical – thermometers and barometers to measure temperature and air pressure, over time have gained more info as temperatures are recorded, also now use balloons and satellites o Pre-Historical - Climate proxy records – record of some natural event that is closely controlled by climate, ex. Wine harvest, price of wheat – most widely used proxy record is distribution of isotopes, particularly oxygen o Sediments/ice: sediments from thousands of years ago preserved in sedimentary rock layers that have not yet subducted and are also preserved in ice, but as Earth changes with plates moving sediments can be mixed, degrading the quality of climate related data it may contain  Deep Antarctic ice sheet layers that extend over 400,000 years  Greenland over 100,000 years, mountain glaciers 10,000 yrs  Fossils used to determine age through isotope dating o Oxygen is16opes: using oxygen to date things18  O forms 99.8% of all oxygen and O accounts for the rest for about a 1/400 ratio and both are in all materials that have oxygen  Variation in isotopes in materials is called fractionation, occurs because of temperature – bonds are stronger in higher mass number  All materials in water have the same isotopic ratio between the material and the fluid, so we can figure out temperature of the ocean 1000 years ago if we can find a material that was in the ocean at that time.  Use oxygen isotope ratios as a geothermometer Climate Models 1. Physical – emphasize things like atmosphere and ocean current variations o Simulate climate today, control case 2. Geochemical – track the movement of distinctive chemical tracers through the system o Used to follow mass movement of Earth‟s materials like sediments, dissolved ions Past Glaciations o Major cold periods “icehouses” o Major extreme periods “greenhouses” o In past 500 million years Earth has experienced 3 intervals of Icehouse conditions, lasting millions of years Glaciers o To form glaciers, need accumulations of snow and ice that exceed the rate of ablation o As the snow ice buildup thickens, it reaches a point where the glacier or ice sheet moves due to slope and pressure of overlying ice, pressure of overlying ice can produce melting at the base that helps it slide o From glacier to ice sheet need: o Cold climate for extensive period o Good supply of precipitation – warm ocean current to polar region o Stable platform upon which to build the structure – large stable continent that allows ice and snow buildup (Antarctica/Greenland) o Sea levels around glaciers/ice sheets will be low as large volumes of water are sitting on the land CHAPTER 13 Icehouse-Greenhouse o Icehouse – times when ice sheets are present on continents o Greenhouse – times when continental ice sheets are absent o Faint Young Sun Paradox – Earth being warm enough in the past to have an abundance of liquid water, even though sun‟s strength was 25-30% less back then o There must have been something else that kept early Earth warm that made the planet habitable Carbon in Rocks o Present day carbon in atmosphere is 390 ppm (390 parts per million units of air) o This carbon comes from human contribution, but mostly from volcanoes emitting 0.15 gigatons per year o Mildly acidic rain (carbonic acid) will break down any rock with Calcium turning it into calcium carbonate, which removes carbon from the atmosphere, so this process could cool down climate by removing CO2 o Plants add to decrease of CO2 by taking it from air and adding it to soil o Chemical weathering in rocks used as a thermostat, lower energy from sun compensated by greenhouse effect in past, now with stronger sun greenhouse effect is less as more CO2 is taken out of the atmosphere. Polar Position Hypothesis o Ice sheets should appear on continents when they are located at or near polar positions o No ice sheets should appear anywhere on earth if no continent exists anywhere near the poles o Gondwana, part of Pangaea, drifted over the south pole from 450- 240 mya but didn‟t have ice – hypothesis not supported for this period o Antarctica has been over south pole since 125 mya but didn‟t have ice sheets until 25 mya – not supported again Pangaea o 350-250 mya: assembly o 240-180 mya: stability o 180 mya: breakup began o Occupied 1/3 of area of Earth, and extended high to north and low to south latitudes, symmetrical at equator o Put a bunch of info into a computer to try to figure out climate during Pangaea, things like sea level, elevation of continent, CO2 level of 1650ppm o Results:  Interior of continent had little precipitation  In the interior seasonal temperatures were extreme, hot winters very cold summers – if glaciers formed they melted o This was climate modeling in its infancy, and applied conclusions to modern day Tectonic Control of CO2 BLAG Hypothesis – by Berner Lasaga and Garrels  When there is lots of active volcanoes and floor spreading, there's high atmospheric CO2, and when there's less spreading and volcanism theses less CO2 in the atmosphere (less activity less CO2, more activity more CO2)  Can determine spreading rates by measuring rock band distances from the central ridge  Good for testing rocks younger than 100 mya Uplift Weathering Hypothesis  Chemical weather viewed as active driver of climate change, not a thermostat  The more surface area, the greater erosion, and the fresher the rock surface the more rapid weathering will take place  Continental collisions correlate with times of ice sheet glaciations for the past 325 million years  When current period of “fossil fuel warming” is over, global climate likely to drop rapidly Ocean Heat Transport Hypothesis  Processes that can change ocean volumes: 1. Changes in volume of ocean floor ridges – higher the ridge the higher the sea level 2. Collision of continents – when continents collide, sea level reduced 3. Construction of volcanic plateaus on ocean floors – basalt spills increase sea levels 4. Water storage in ice sheets – Antarctica melts would cause seas to rise 66m 5. Thermal expansion of water – water expands when heated  Hypothesis states that sea levels can control long term icehouse- greenhouse climates: high water levels cause warmer climates, low water levels cause cooler climates o Criticism of the hypothesis:  Low sea levels should lead to more extreme warm/cold periods and if glaciers grew during winter they would be melted in hot summer  High sea levels should lead to moderate climates, but this does not happen in wet maritime areas as they promote ice growth in winter, growth of ice sheets at high latitudes Snowball Earth  Good geological evidence there was ice on continents near the equator several hundred million years ago – meaning the whole of Earth‟s surface was at or close to freezing point  To address this controversy, must be able to age date rocks containing the glacial evidence and determine latitude positions of the land masses containing the ice  Problem is reliability of latitude data  Consensus is that ice sheet bearing continents were just barely in the tropical area and near tropics it wasn‟t frozen maybe slush – “Slushball Earth” model  Back to snowball Earth, it would have heated again though spreading and volcanism putting CO2 into the oceans, once oceans saturated in CO2 it find its way out to the atmosphere leading to a stronger greenhouse effect so Earth heats and melts the snow  Thermostat always there, when earth is cool it will heat, when it is too hot it will cool Paleocene-Eocene Thermal Maximum (PETM)  Eocene Optimum a 6 million year period when earth was warm until temps dropped significantly and ice sheets forming 35 million years ago  On the Eocene Optimum big spike in temperatures – PETM – lasting for about 20,000 years where ocean temps raised by 6 degrees initiated by an event that only took 1000 years  Some event released 2000 gigatons of carbon into the atmosphere (same amount as co2 emissions today)  Waters at this time circulated in ways that prevented the formation of ice sheets Effects  Global temps increased 6 degrees, seas 22 degrees in arctic summer  Sea levels rose from thermal expansion of water  Circulation was different, water flowed south to north warming the deep ocean basins dramatically, opposite today  Extinction of close to 50% of deep ocean formanifera, but land mammals in abundance Possible Causes  Volcanic activity degassing mantle  Comet rich in carbon impacted earth  Burning of large volume of peat (early coal) – not possible  Orbital anomaly repeated over and over – no  Release to the atmosphere of large volumes of methane (CH4) o Methane comes from decay of marine life, escapes to atmosphere as CO2 and water o On cold ocean floors methane combines with water to form methane clathrate o As ocean floor temperature rises or pressure decreases, methane clathrate breaks down, releasing CO2 into the atmosphere, raising temperatures o This release of methane is responsible for the PETM and lasted for about 1000 years Current Icehouse  Currently go back and forth between glacial and interglacial periods  Clearly the big cycles of glaciations correspond with the 100,000 year cycles Milankovitch was talking about, also the 41,000 year cycle, and on a smaller scale would see the 23,000 year cycle as well  Past 35 million years CO2 has been decreasing (not including human industrial capacity)  Most recent glacial period began 110,000 years ago and was over by 12,500 years ago Younger Dryas Event  Dramatic cooling event well documented in pollen records from Arctic plant called Dryas in Europe – 13,000-11,700 years ago in North Atlantic  Freshwater lakes formed in depressions of glaciers, overflowed and spilled onto the denser salt water  Cold surface melt water reduced evaporation, pushed cold air across Europe Little Ice Age  1000-1300 Medieval Climatic Optimum warm climate  In 1400 when climates got colder shipping in North Atlantic stopped.  Only about 1 degree colder than now, but much harsher conditions esp. in winter  Getting cooler and cooler Millennial Oscillations  Events as short as 1000 years in duration, first was the Young Dryas Event  Events that appear to not be explained by Milankovitch orbital factors  3 hypotheses  Natural oscillations inherent in the internal behaviour of northern ice sheet  Result of internal interactions among several parts of the climate system  Response to solar variations external to the climate system  Origin of millennium oscillations unknown, but may be correlated with periods of frequent ice rafting El Nino  Name given to an ocean circulation pattern in Pacific Ocean that recurs every 2 to 7 years  During El Niño years effects on sea life and humans on South American coast is devastating as strong winds fail to blow in eastern and tropical Pacific, upwelling doesn‟t occur, and surface waters near coast are warm, large amounts of moisture lead to floods and natural disasters Sunspots  Appear as dark spots on sun‟s surface  Appear on roughly 11 year cycle, being monitored for about 400 years  Tracks pattern of disturbance of magnetic field orientation  Unlikely it had any effect on the Little Ice Age Humans and Climate Change  CO2 concentration in atmosphere at 280ppm and remained for thousands of years  Around 1800 CO2 values began gradually increasing and accelerating  Land clearing and burning of fossil fuels the primary processes o Burning wood directly produces CO2, less vegetation leads carbon levels to sink  Biosphere capable of removing great quantities of atmospheric CO2  Biosphere cannot remove as much CO2 as is being added annually  Methane is also increased in today‟s atmosphere o Released as natural gas in coal mining and oil drilling  “Door to hell” – 35 years ago drilling for natural gas in Uzbekistan, drill collapsed the roof of an underground cavern o Crew set the gas on fire, worried it was poisonous, has burned steadily contributing to atmospheric gas ever since  3 reasons as to amount of CO2 in atmosphere today 1. Warming trend solely due to greenhouse effect induced by human activity 2. Has been a slow natural climatic trend, small human contribution to greenhouse effect 3. Has been a slow natural climatic cooling trend, so human contribution to greenhouse is very large o Reality lies between 1 and 3, 2 has no evidence o Climatic scientists try to solve the problem by first looking at natural trends then looking at volumes of gasses evolved from human activity and assessing their effect as greenhouse contributors o Consensus is that to date added CO2 should account for 2.5 degrees Celsius of global warming, at most 4.5 at least 1.5 o 1800-1870: 13.6 C o 2009: 14.5 C Next 100-1000 years o CO2 levels will continue to rise and global climate will continue to warm o Over the next millennium orbital variations (Milankovitch factors) will produce cooling but maximum effect will be decrease temp of .2 degrees, insignificant in the face of a strengthened greenhouse o 2xCO2 and 4xCO2 scenarios, times the amount of CO2 from pre- industrial levels o These models project that human technology exi
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