Global Warming

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Global Warming

  • the term used for the rapid increase in global temperature over the last century
  • it is a type of climate change - a significant chnage in the weather of a region over a period of at least several decades
  • it can cause different types of climate change e.g. changing rainfall patterns and seasonal cycles
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Temperature Records: 

  • since the 1850s, temperature has been measured aound the world using thermometers, which gives a reiable but short term record of global temperature change


  • is a method used to find out how old a tree is by counting tree rings (most trees produce one ring within their trunk per year)
  • the thickness of the ring depends on the climate when it was formed (warmer = thicker)
  • scientists take cores through tree trunks and date them, then see what the climate was like each year
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Pollen in Peat Bogs:

  • pollen is oftern preserved in peat bogs, which accumulate in layers (so the age of the preserved pollen increases with depth)
  • scientists take cores from the bogs and extract pollen grains from the different aged layers, then identify the plant species the pollen came from
  • only mature (fully grown) plant species produce pollen, so the samples only show the species that were successful at that time
  • scientists know the climates that different plant species live in now - when they find preserved pollen from similar plants, it indicates the climate was similar when the pollen was produced
  • because plant species vary with climate, the preserved pollen will vary as the climate changes over time
  • a gradual increase in pollen from a plant species that's more successful in warmer climates would show a rise in temperature (a decrease in pollen from a plant that needs cold conditions would show the same thing)
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  • scientists believe that the recent increase in global temperature (global warming) is caused by human activity, which has enhanced the greenhouse effect (greenhouse gases absorbing outgoing energy, so less is lost to space)
  • the greenhouse effect is essential to keeping the planet warm, but too much greenhouse gas in the atmosphere means the planet warms up
  • two of the main greenhouse gases are carbon dioxide (CO2) and methane (CH4)
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Carbon Dioxide:

  • atmospheric CO2 concentration has increased rapidly since the mid-19th century fro 280 ppm (parts per million) to nearly 380 ppm - the concentration had been stable for the previous 10,000 years
  • COconcentration is increasing as more fossil fuels are being burnt
  • COconcentration is also increased by the destruction of natural sinks (things that keep CO2 out of the atmosphere by storing carbon) COis released when trees are burnt, or when decomposers break down the organic compounds and respire them
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  • atmospheric methan concentration has increased rapidly since the mid-19th century from 700 ppb (parts per billion) to 1700 ppb in 2000 - the level had been stable for the previous 850 years
  • methane concentration is increasig because more methane is being released into the atmosphere eg. because more fossil fuels are being extracted, there's more decaying waste, there are more cattle which give off methane as a waste gas
  • methane can also be released from natural stores e.g. frozen ground (permafrost) as temperatures increase, it's thought these stores will thaw and release large amouts of methane into the atmosphere
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  • it's agreed that global warming is happening - there has been a rapid rise in global temperature over the past century
  • it's also accepted that human activity is increasing the atmospheric COconcentration (the scientific consensus its increase is causing the increase in global temperature
  • soem scientists have drawn a different conclusion from the data on atmospheric CO2 concentration and temperature - they think that COisn't the main cause of the global temperature increase
  • the conclusions scientists reach can be affected by how good the data is that they're basing their conclusions on (reliability/evidence/ bias)
  • biased conclusions are subjective as they've been influenced by an opinion instead of only being based on evidence
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Rising Temperature

  • an increase in temperature will affect the metabolism of all organisms (enzymes, temp increase to optimun, above = denature)
  • increased temperature will speed up the metabolic reactions of some organisms, increasing their rate of growth and progression through life cycles
  • the temperature will be too high for some organisms, so their metabolic reactions will slow down, decreasing thier rate of growth and slowing progression through their life cycles
  • global warming will also affect the distribution of some species - all species exist where their ideal conditions for survivial are - when these conditions change, they'll have to move to a new habitat where the conditions are better (if they can't move, they die out in the area) the range of some species may expand if conditions in previously uninhabitable areas change
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Changing Rainfall Patterns

  • global warming will cause some areas to get more rain and other to get less
  • this will affect the life cycles of some organisms e.g. ocotillo (desert plant) is dormant during dry periods but becomes active and grows new leaves when there is rainfall - reduced rainfall will cause ocotllo to remain dormant longer
  • changing rainfall patterns will also affect the distribution of some speies e.g. deserts could increase in area if rainfall decreases - species not adapted to deserts will have to move to new areas so they won't die out

Seasonal Cycles

  • organisms are adapted to the timing of the seasons and the changes that happen (temperature change and availability of food)
  • change in seasonal cycles will affect the life cycles or some organisms, as well as their distribution (birds flying south for the winter)
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Core Practical: Effect of Temperature on Organisms

Seedling Growth Rate

  • plant seedlings in soil trays and measure the height of each seedling
  • put the trays in incubators at different temperatures
  • control variables: water content of soil, light intensity, CO2 concentration
  • after a period of incubation, record the change in height of each seedling and calculate avaerage growth rate (avaerage change in seedling height in each tray ÷ incubation period)

Brine Shrimp Hatch Rate

  • put equal number of brine shrimp eggs in water baths set at different temps.
  • control variables: volume of water, salinity of water Oconcentration
  • number of hatched brine shrimp in each water bath are recorded every five hours and hatch rate is calculated (number of hatched brine shrimp in each water bath ÷ number of hours)
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The Carbon Cycle

  • carbon (in the form of CO2 from the atmosphere) is absorbed by plants during photosynthesis and becomes carbon compounds in plant tissues
  • carbon is passed on to animals when they eat the plants and to decomposers when they eat dead organic matter
  • carbon is returned to the atmosphere as all living organisisms caryy out respiration which produces CO
  • if dead organic matter ends up in places where there aren't any decomposers (deep oceans/bogs) the carbon compounds can be turned into fossil fuels over millions of years (by heat and pressure)
  • the carbon in fossil fuels in released as COwhen they're burnt (combustion)
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Reducing Atmospheric CO2


  • are produced from biomass - material or waste that is or was recently living
  • are burnt to release energy, which produces CO2
  • there's no net increase in atmospheric CO2 concentration when biofuels are burnt
  • using biofuels as an alternative to fossil fuels stops the increase in atmospheric CO2 concentration caused by fossil fuels


  • is the planting of new trees in existing forests that have been depleted
  • more trees means more CO2 is removed from the atmosphere by photosynthesis
  • COis converted into carbon compounds and stored as plant tissues in the trees, meaning more carbon is kept out of the atmosphere, so there's less CO2 to contribute to global warming
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Reducing Global Warming

Increase the use of biofuels

  • farmers - some governments fund that farming of crops for biofuels
  • drivers - the price of biofuels is usually lower than oil-based fuels
  • consumers - using farmland to grow crops could cause food shortages
  • conservationists - forests have been cleared to grow crops for biofuels

Increase the use of wind turbines

  • companie making turbines - their sales would increase
  • environmentalists - turbines produce electircity without increasing atmospheric CO2 concentration
  • local communities - some people think turbines ruin the landscape
  • bird conservationists - many birds are killed by flying into turbines
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  • an international group of scientists (IPCC) has extrapolated data on atmospheric CO2 condition to produce a number of emissions scenarios - predictions of how human CO2 emissions will change up to 2100
  • the secnearios include emissions:
    • continuing to grow as they are now
    • increasing by a lot
    • being controlled by management strategies
    • not increasing much more
  • they can put all these different scenarios into global climate models (computer models of how the climate works) to see how much global temperature will rise with each scenario
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Limitations of Predictions

We don't know:

  • how CO2 emissions will change (which emissions scenario is most accurate)
  • exactly how much each emissions scenario will cause the global temperature to rise by
  • howmuch change in atmospheric CO2 concentration is due to natural causes (without human influence)
  • what attempts there will be to manage atmospheric CO2 concentration, or how successful they will be
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