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McGill University
GEOG 205
Gail Chmura

GEOG 205Global Change Past Present and FutureMidterm Notes Winter 2013 UNIT 1 PRESENT Thomas Maltuspopulations grow exponentially but power to support them doesntpositive checks things that increase mortality rates hunger disease warpreventative 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 USChina have low fertility rates due to immigration and the one child rule3 stages influencing population growth o stage 1nonindustrial country where birthdeath rates high with industrialization birth rates highdeath rates drop o stage 2high population growth standard of living increases more educationfamily planning o stage 3birth 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 needscarrying capacity the maximum number of individuals of a species that can be sustained by an environment without lessening the environments ability to sustain the same number of individuals in the future o depends on how we want to livehow we want those who follow to live o most environmental damage from very large number of people on earth environmental challenges o biodiversityspecies declining o deforestation80 original forests cleareddamagedfragmented o waterindustrial wastes dumped into waters of developing countries o air pollutionkilling moremore peopleamount of people living in urban areas increasingWilliam Cronondivide between urban dwellersimpacts of major environmental problemsenergy consumption increasing over timein past humans lived rural lifestyle hunting agriculture but now rely on energy to power homes cars processes technology etcthe Gaia hypothesis a metaphor that the environment at global levels has be changed by life throughout historythe changes have improved the chance that life on earth will continuelife 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 atmospherecombination of temperature humidity cloudinessclimate weather informationhow the atmosphere typically behaves over long periods of timeprecipitation expected temperature etccauses and effects of global warming can be changed through adaptationmitigation o adaptation aimed at reducing the effects GEOG 205Global Change Past Present and FutureMidterm Notes Winter 2013 o mitigation aimed at reducing the causes James Hansen began to think about impacts of airborne particles from volcanoesblock the radiation from the sun so darkened earths surfacetherefore cooled itMilankovitch theorydescribes collective effects of changes in earths movements on climate o eccentricitythe earth doesnt orbit around the sun in a perfect circle period of 100 000 years o axial tilt changeschange of the earths tilt every 41 000 years leads to different amounts of radiation low axial tiltsmall seasonal variation in solar insolationhigh axial tiltlarge seasonal variation in solar insolation o precessionchange in orientation of earths orbit every 26 000 years one square metre of earth directly faces sunreceives 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 landocean surfaces o 84 remains to heat surface earth balances incomingoutgoing radiationcalculations show planet should be 6C to maintain balance which is 20C colder than realityo sunlight attenuated gradual loss of intensity by scatteringabsorption through atmosphere o difference due to greenhouse effectgreenhouse gas molecules vibrateabsorb heatgases 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 gasescloud radiative forcing change in average net radiation at top of troposphere due to presence of cloudsfeedbacks factors which tend to increase rate of a process positive or decrease it negativealbedo measure of surface reflectivity possible causes of recent climate change o astronomicchanges in earths orbit increasing solar radiation not true since suns radiation decreasingclimate increasing o volcanic activityepisodicirregular production of ashchemicals that block solar radiation so have cooling effecto land usechanges from natural vegetation to grazing land agricultural crops bare soilurban areas decreases albedoincreases proportion of radiation transformed into sensible heato circulation patternsEl NinoLa Nina o atmospheric chemistrygreenhouse gases warm the earth but also add more reflectivecloud 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
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