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Midterm Notes

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McGill University
GEOG 205
Gail Chmura

GEOG 205 – Global Change: Past, Present and Future – Midterm Notes Winter 2013 UNIT 1: PRESENT  Thomas Maltus  populations grow exponentially but power to support them doesn’t  positive checks: things that increase mortality rates (hunger, disease, war)  preventative checks: things that decrease fertility rates (abortion, birth control, celibacy)  fertility rates: average number of children a woman is expected to have based on where they are in the world  Canada, US & China have low fertility rates due to immigration and the one child rule  3 stages influencing population growth o stage 1  non-industrial country where birth & death rates high; with industrialization, birth rates high & death rates drop o stage 2  high population growth; standard of living increases, more education & family planning o stage 3  birth rates drop toward death rates; zero or negative growth becomes normal; few children in families  sustainability: development which meets needs of current generations without compromising ability of future generations to meet their own needs  carrying capacity: the maximum number of individuals of a species that can be sustained by an environment without lessening the environment’s ability to sustain the same number of individuals in the future o depends on how we want to live & how we want those who follow to live o most environmental damage from very large number of people on earth  environmental challenges o biodiversity  species declining o deforestation  80% original forests cleared/damaged/fragmented o water  industrial wastes dumped into waters of developing countries o air pollution  killing more & more people  amount of people living in urban areas increasing  William Cronon  divide between urban dwellers & impacts of major environmental problems  energy consumption increasing over time  in past humans lived rural lifestyle (hunting, agriculture) but now rely on energy to power homes, cars, processes, technology, etc.)  the Gaia hypothesis: a metaphor that the environment at global levels has be changed by life throughout history & the changes have improved the chance that life on earth will continue  life manipulates the environment for the maintenance of life  James Lovelock argued atmospheric composition can be used to test for presence of life by comparing gases with those based on biological activity  Daisy world hypothesis: under low temperatures, black daisies have advantage since absorb radiation; under high temperatures, white daisies have advantage since reflect radiation  weather: day to day variation in the state of the atmosphere  combination of temperature, humidity, cloudiness  climate: weather information & how the atmosphere typically “behaves” over long periods of time  precipitation, expected temperature, etc.  causes and effects of global warming can be changed through adaptation & mitigation o adaptation: aimed at reducing the effects GEOG 205 – Global Change: Past, Present and Future – Midterm Notes Winter 2013 o mitigation: aimed at reducing the causes  James Hansen began to think about impacts of airborne particles from volcanoes  block the radiation from the sun so darkened earth’s surface & therefore cooled it  Milankovitch theory  describes collective effects of changes in earth’s movements on climate o eccentricity  the earth doesn’t orbit around the sun in a perfect circle, period of 100 000 years o axial tilt changes  change of the earth’s tilt every 41 000 years leads to different amounts of radiation  low axial tilt = small seasonal variation in solar insolation  high axial tilt = large seasonal variation in solar insolation o precession  change in orientation of earth’s orbit every 26 000 years  one square metre of earth directly faces sun & receives 1370 watts of energy but most receive 342 watts o 6% scattered back to space by atmospheric particles o 10% reflected back to space by land & ocean surfaces o 84% remains to heat surface  earth balances incoming & outgoing radiation  calculations show planet should be -6C to maintain balance which is 20C colder than reality o sunlight attenuated (gradual loss of intensity) by scattering & absorption through atmosphere o difference due to greenhouse effect  greenhouse gas molecules vibrate & absorb heat  gases at top of atmosphere cold so emit less radiation but capture more from earth  radiative forcing: change in average net radiation at top of troposphere due to change in concentration of greenhouse gases  cloud radiative forcing: change in average net radiation at top of troposphere due to presence of clouds  feedbacks: factors which tend to increase rate of a process (positive) or decrease it (negative)  albedo: measure of surface reflectivity  possible causes of recent climate change o astronomic  changes in earth’s orbit; increasing solar radiation (not true since sun’s radiation decreasing & climate increasing) o volcanic activity  episodic & irregular production of ash & chemicals that block solar radiation so have cooling effect o land use  changes from natural vegetation to grazing land, agricultural crops, bare soil & urban areas; decreases albedo & increases proportion of radiation transformed into sensible heat o circulation patterns  El Nino & La Nina o atmospheric chemistry  greenhouse gases warm the earth but also add more reflective & cloud forming particles that cool the earth  the greenhouse effect: water vapour, carbon dioxide, etc. absorb some of the thermal radiation leaving the surface of the earth, and in turn heat up the earth o there is a natural greenhouse effect since all gases there before human beings, but the enhanced greenhouse effect is due to added effect of human activities GEOG 205 – Global Change: Past, Present and Future – Midterm Notes Winter 2013  clouds reflect radiation from sun back to space, but also absorb thermal radiation  two effects working opposite each other but in general, clouds slightly cool the earth’s surface  runaway greenhouse effect: interior of Venus contains a lot of water vapour which forms the atmosphere, and creates a greenhouse effect; the temperature rises because of this which leads to more evaporation and therefore higher increases in temperature; process continues until atmosphere saturated with water vapour o Venus closer to sun so started at a warmer temperature  won’t happen to earth  temperature anomaly: departure from a reference value or long term average o positive anomaly: observed temperature warmer than reference value o negative anomaly: observed temperature colder than reference value  urban heat isle effect: metropolitan area which is significantly warmer than its surrounding rural areas due to buildings blocking surface heat from radiating into cold sky, thermal properties of materials absorbing more & lack of evapotranspiration through lack of vegetation  characteristics of rate of growth of proxie materials (ice cores, tree rings, pollen, etc.) influenced by climatic conditions  future precipitation & storm changes will vary by season & region th  aphelion: when the earth is farthest from the sun (July 4 )  perihelion: when the earth is closest to the sun (January 4 )  there is an equatorial surplus of energy which is transferred poleward through atmospheric & oceanic circulation  atmospheric circulation patterns due to differences in pressure & unequal heating of earth’s atmosphere  air moves to the warmer location (less dense)  latitudinal circulation established as Hadley cells  warm air rises at equator & falls at 30 degrees  Coriolis Effect: direction of air motion on a global scale is affect by the earth’s rotation o flows to the E in northern hemisphere & to the W in southern hemisphere o strongest near poles & decreases to zero at equator  polar front: where subtropical air meets polar air  land ocean effect: ocean retains temperatures longer than land surfaces; land heats up more quickly; hot/low pressure air rises & ocean’s low pressure moves in  opposite happens in winter  ocean circulation patterns driven by atmospheric circulation  thermohaline circulation = the global conveyor belt o slow movement of water between Pacific & Atlantic o transfers warm water from equatorial Atlantic to North Atlantic where it cools & becomes denser with salt to sinks o this water then travels to Southern Ocean  upwelling & mixing occur to deep waters brought to surface of Indian & Southern Pacific oceans o circulation loop moves surface water from Pacific past Australia into Indian Ocean to complete circuit o important transfer mechanism for heat from equator to northern hemisphere  changes in circulation patterns = El Nino Southern Oscillation (ENSO) o occurs every 3-7 years o cold upwelled waters replaced by warm current o brings droughts, heavy rain falls, severe spells of heat & cold, high incidence of cyclonic storms GEOG 205 – Global Change: Past, Present and Future – Midterm Notes Winter 2013 o normal, cold water brings nutrients for marine life but warm, sterile water from the west causes marine life to disappear o usually wind blows from E to W along equator, piling up water in western part of Pacific ocean o trade winds lose strength in spring so less water pushed west  water begins to heat up o trade winds replenished by Asian summer monsoon but sometimes not & even reversed (W-E) o in eastern part, deeper/colder water pulled up from below to replaced water pushed west o in El Nino, winds pushing water get weaker so warm water piled up in W goes back to E & not as much cold water gets pulled up from below o water in eastern Pacific is warmer o importance to climate change  illustrates natural changes in circulation patterns  linked to extreme weather events globally  coincides with faster rises in global temperatures & atmospheric CO2 increases  example of teleconnection in global climate system  pattern of surface ocean currents related to prevailing surface winds  energy transferred from wind to water by friction of air moving over the surface o gyre: large circular movements in the ocean current system; track movements of air around subtropical high pressure cells o westward equatorial currents mark belt of trade winds  approach land, turn poleward o eastward movement of water over westerlies zone = west-wind drift  brings cool water to equator & poles  comparing climates relies on temperature & precipitation  temperature regime: distinctive types of annual temperature cycles related to latitude and location o each labelled according to latitude zone: equatorial, tropical, mid-latitude, subarctic  5 climates: 4 defined by temperature, 1 defined by precipitation o (A) tropical rainy  hot, no winter, rainfall exceeds evaporation o (B) dry  evaporation exceeds rainfall o (C) mild, humid  distinct summers & winters; coldest months between -3C & 18C o (D) snowy forest  coldest month below -3C o (E) polar  no summer  temperature variations happen due to latitude & whether location is coastal or continental (different rates of heating & cooling between ocean and land)  precipitation variations happen due to air temperature, air masses & their movements, position relative to coast, & elevation  biggest factor = air masses & their movements  3 main classes of precipitation o uniform o maximum during high sun (summer) o maximum during low sun (winter)  there are 7 global precipitation regions o wet equatorial belt  equator; heavy rainfall due to temperatures & convection patterns, frequent thunderstorms (Amazon River basin, Congo River basin, East Indies) o trade-wind coasts  eastern side of continents, trade winds bring warm air causes orographic rain, 1500-2000 mm annually (Madagascar, Queensland AU, Central America) GEOG 205 – Global Change: Past, Present and Future – Midterm Notes Winter 2013 o tropical desert  centred on Tropics from west coast eastward & northward in interior, hot/clear/barren skies, 250-500 mm annually, Baja California, Namibia desert o midlatitude deserts & steppes  interior NA & Asia, desert & semi-air grasslands, 100-500 mm, moister air from coasts warm & dry as descend from mountains; BC, Oregon, Washington o moist subtropical  SE side of continents; 1500-2000 mm annually, caused by position on western margins of oceanic subtropic high pressure cells, subject to cyclones, Alabama, Florida o midlatitude west coast  west coasts of continents, prevailing westerly winds hit mountains &
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