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Global Climate Change (Global Climate Change (Enhanced greenhouse effect:
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Global Climate Change
Global Climate Change
Natural greenhouse effect:
- visible light absorbed by surface which warms up
- warmed surface emits infrared radiation, can't pass through atmosphere easily
- greenhouse gases better at absorbing infrared
- CO2 and water vapour most important
- natural effect keeps earth warm
Enhanced greenhouse effect:
- human activities increase concentration of greenhouse gases that absorb infrared and warm atmosphere
Methane; anaerobic respiration by microbes in padi fields, landfill sites, intestines of livestock, produced during formation of fossil fuels, released by ventilation of coalmines, leaks from natural gas fields and pipelines
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CO2; combustion of fossil fuels and wood, ploughing of soils, drainage of marshes and bogs
Oxides of Nitrogen; oxygen and nitrogen react in air at high temperatures e.g vehicle exhausts, power stations, released into atmosphere as exhaust gases, fertiliser use can also increase NOx emissions including nitrous oxide
Chlorofluorocarbons (CFCs); used as aerosol propellants, fire extinguishers, refrigerators, solvents and in expanded foam plastics
Consequences:
- relatively small temp rise involved in climate change may have direct and indirect impacts on abiotic and biotic conditions on earth.
Changes in Climatic processes:
- retention of more heat energy in atmosphere produces changes in atmospheric pressure and evaporation of water, produces new weather patterns
Wind pattern changes:
- Jet streams
- strong winds blowing from west to east along meandering path in upper troposphere
- caused by difference in temp and density between two air masses e.g warm air in mid latitudes and cold air in polar regions
- wind blows to equalise pressure differences
- don't blow in straight line from high to low pressure areas due to earths rotation which causes Coriolis force causes wind to blow in spiral fashion
- control movement of air bodies which create rain e.g cyclonic storms carried across Atlantic to UK
- Polar regions warming faster than areas near equator
- so temp differences that cause jet streams getting smaller
- Jet streams in Northern Hemisphere moving nearer to pole, more slowly, and more meandering path
- Waves created by meandering path called Rossby waves, they carry unusually cold air south/ warm air north
- slower movement can mean weather systems to remain over an area
- creates longer, more intense weather e.g prolonged droughts/ increased rainfall = floods
Changes in rainfall:
- increased temp causes more evaporation which = more precipitation
- higher temps means air has to move further towards cold area before water vapour cools enough to condense and fall
- changes in wind direction and velocity carry humid air to new areas = increased rain in one area decreased in another
Ecological changes:
- species affected directly by temp, changes to species they rely on, changes to natural processes affecting them
- temp rise causes plants to grow faster
- provides more food
- toxins are built up in plant leaves to protect from being eaten, if growths earlier these may build up sooner killing insects e.g caterpillar
- precipitation changes shrink/enlarge wetland habitats
- oak trees can survive drought due to deep roots
- dormouse hibernation disturbed by warmer winters, use stored fat, starve before spring
- timing of ecological events e.g flowering, migration and nesting may change
- survival of interdependent species reduced
- e.g if pollinating insects emerge earlier/ later they wont be present when flowers are produced
- distribution of species changes as they colonise areas that have become suitable, not possible for all if;
- they colonise new areas slower than their old ones disappear, especially likely for trees
- no suitable new areas avaliable
- human land use blocks movement
- live in interdependent communities, not all move at same speed
- Species most likely to be affected are those closes to edge of range of tolerance
- some species not affected by physical environment changes but species they depend on
- e.g change in food supply, predation, disease, survival of pollinators or seed dispersal insects
Bats in UK:
- warmer, shorter winters increases survival during hibernation
- warmer weather increases population of food species, espc night flying insects
- wetter, stormier weather reduces time they can feed, reducing survival
- population of a species may decline in one area leading to local extinction but survival may improve in other areas, may then colonise new areas and increase its range
- colonisation only possible if suitable new areas exist and there's a biological corridor linking areas
- birds/flying insects easily colonise new areas, plants and less mobile animals don't
- with conditions changing, small populations become become isolated from rest of population
- e.g with sea level rising, islands created
- temp rise, isolated populations retreat up to cooler mountain areas
- May be little/no population movements between isolated populations which leads to problems threatening future survival such as;
- gene pool divided into smaller groups, inbreeding likely
- not possible for surplus individuals from other areas to repopulate where local population died out
- overall pop may be large enough to be viable, smaller pops may not be
- increase in concentration of greenhouse gases predicted to have significant effect on abiotic conditions on earth and survival of species
- simplest effect is absorption of IR energy emitted by earth's surface which is then converted to heat warming atmosphere
- temp rise might be small but affects other processes which have big impacts on earth
- mean global temp rise over past 100 years is 1 degree but further rise of 2 degrees is predicted to have serious consequences
Changes in cryosphere:
- warmer temp have direct effect on ice on earth as it melts more rapidly
- but also increased precipitation including snow
- some extremely cold areas have low snowfall as precipitation falls before it gets there
- higher temp allows more precipitation in these areas
Reduction is amount/duration of snow cover:
- reduced amount of ice and snow and length of time it remains on ground before melting
- reduced albedo of surface so less sunlight reflected away and more absorbed = further heating
Extent and speed of movement of land ice:
- snow falls on land collects, compacts into ice, flows gradually downhill when mass has built up, forms glacier
- as moving ice reaches lower altitudes, it warms up & melts
- may reach sea before melting, produces ice bergs as glacier breaks up
- may melt before sea and add to river flow
- warmer temp cause front end of glacier to melt faster than it's moving so ice front retreats up valley
- meltwater from surface of glacier may flow through cracks in ice to bottom of glacier which lubricates ice as it slides over rock, moves quicker
- if increased speed due to lubrication is greater than the faster melting the glacier will move further down the valley
- despite extending further, total volume of ice in glacier may fall if no increase in snowfall where it's formed
- retreating and extending glaciers are evidence of warming temps
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Loss of ice shelves:
- land ice flows into sea, floats and breaks off to form icebergs
- sea levels rise means land ice doesn't move as far before floating off into sea
- some ice sheets grounded on sea bed may float and break up earlier as levels rise
- broken up ice shelves don't directly raise sea levels as they're floating and have already displaced water
- ice sheets that are grounded on sea bed block movement of ice on land
- once ice shelf has broken up, glaciers or ice sheet behind flow more rapidly towards sea
- ice sheets e.g West Antarctica are held back by ice shelves , so vulnerable to rises in temp and sea level compared to East Antarctica which is more completely on land with few ice shelves
Ice thickness and area:
- during Arctic/Antarctic winters the area of ice that forms on sea surface increases as temperature drops
- area of ice forming declines as temps rise
- area of sea ice that forms each winters increased in recent years, due to increased freshwater flowing off land , floating on denser sea water then freezing
- melting ice means lower albedo so more sunlight absorbed so further heating
Ice Lakes:
- water produced by melting ice collects on surface of glaciers producing ice lakes
- if front ice wall of lake melts, water's released, causes sudden flooding
- threat e.g in Himalayas as large human population living downstream
Ice and snow fed rivers:
- reduced snowfall and increased rainfall affects river flow patterns
- snow may build up gradually and melt gradually
- rivers fed by melt water have more even flow that ones fed by rain
- snow instead of rain means snow accumulates which can cause big increase in river flow if climate suddenly warms
Sea level rise:
Thermal expansion of seawater -
- warmer atmosphere heats water which then expands, sea level rises
- takes long time due to quantity of water in oceans and its high specific heat capacity
- water at surface warmed by direct contact with atmosphere
- cold deep water only heats up when slow ocean currents bring it to surface
Melting land ice -
- ice floating on surface doesn't raise sea level when it melts as it contracts while melting and occupies same volume as ice that was below water level
- ice that's on land causes level rise as it increases volume of water flow
Changes in ocean currents:
- important in distributing heat around planet
- big influence on climate
- caused by processes in atmosphere
- winds move surface water
- evaporation causes water to flow to replace whats evaporated
- heating/cooling changes density of surface water , affects ease surface water sinks
- changes in salinity caused by evaporation/ inflow of freshwater from melted land ice affects water density
The North Atlantic Conveyor (the 'Gulf Stream'):
- involves movement if layers of surface and deep water in North Atlantic Ocean which distribute heat energy and control climate
The natural North Atlantic Conveyor:
- warm water from tropical Atlantic Ocean travels north-east to north-west Europe, two processes drive movement ~
- friction with prevailing winds blowing over ocean surface from South West to North East, surface water flows in same direction
- water in North East Atlantic sinks as it cools and becomes less dense, draws water in to replace it
- UK warmed by North Atlantic Conveyor, brings warm water to tropical regions, prevents cold weather in regions of same latitude e.g Canada
Changes in North Atlantic Conveyor caused by global climate change:
- higher atmospheric temp cause land ice to melt and flow into sea
- dilutes sea causes salt concentration to go down
- less saline means less dense so less likely to sink
- reduces flow rate of water current
- NW Europe will become colder
El Nino:
- El Nino is the name given to a sequence of events which occur naturally, around every 2-7 years but are becoming more frequent, possibly due to Climate change. Name from Spanish meaning Christ child as they usually start around Christmas.
- normal conditions 'reliable trade winds' blow westward across the Pacific Ocean near the equator moving surface ocean current in same direction. Causes deep cold water drawn upwards near coast of South America. Water from deep ocean is rich in nutrients causing algal bloom near the surface which feeds a rich food web including important commercial fisheries providing food for humans.
- Current continues moving west becoming warmer, moves south along east coast of Australia as warm current
- current also affects rainfall patterns, water temp is major determinant of whether rain will fall. If current at coast is cold any water bearing winds heading over sea towards land will be cooled so water vapour may condense and fall as rain before reaching land
- if warm coastal current wind retains water vapour and falls as rain on land
- when the winds reverse direction so ocean currents slow or reverse this stops the nutrient upwelling so the rich food web collapses. The temp drop in western Pacific and increase in eastern Pacific changes distribution in rainfall, reduced in eastern Australia, coastal South America has floods and heavy rain where it's usually deserts
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