Unit 4: Section 3- Global Warming

A summary of the global warming and climate change topic from Edexcel A2 biology

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Introduction to Global Warming

  • Global warming- the rapid increase in global temperature over the last century. A type of climate change
  • Evidence for climate change
  • Temperature records- Global temperature has been measured with a thermometer since 1850- giving a reliable but short term record
  • Dendrochronology (tree rings)- method for figuring how old trees are using rings (produced at a rate of one a year). 
  • The thickness of ring depends on the climate- when it's warmer the rings are thicker.
  • Cores taken from trees show that the most recent things are the thickest, and get steadily thinner the further in the past they were formed
  • Pollen in peat bogs
  • Pollen is preserved in peat bogs. Bogs accumulate in layers so the age of pollen increases with depth. 
  • Pollen grains can be extracted and the plant species can be identified. Only fully grown plants produce pollen, so samples only show the successful species at the time
  • The differences in pollen species over time can show how the climate has changed eg. if there is gradual increase in pollen from a plant species which is more successful when it is warmer, it suggests the temperature has risen
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Causes of Global Warming

  • The scientific consensus is that the recent increase in global temperature is caused by human activity. It has been caused by humans enhancing the greenhouse effect.
  • Too much greenhouse in the atmosphere means less infrared is lost to space. The main greenhouse gases are methane and CO2
  • CO2 is increasing rapidly as more fossil fuels are burnt for electricity, heating, transport and resources. It is also increased through the destruction of carbon sinks (things that keep C out of the atmosphere through storing it) eg. trees
  • Methane is increasing due to more fossil fuels being extracted, more decaying waste and more cattle releasing CH4 as waste gas. It can also be released from natural stores, in frozen ground called permafrost. Rising temperaures may cause thawing and release of CH4
  • When interpreting on evidence for climate change, you should describe the data, and then draw a conclusion
  • It has been agreed that temperatures are rising, and that human activity is increasing atmospheric CO2 concentration. But not everyone agrees that rising CO2 is the main cause of global warming.
  • Conclusions are affected by how good the data is, how much evidence there is, and bias
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Effects of Global Warming

  • Rising temperature- An increase in temperature will mean metabolic reactions in some organisms speed up, so rate of growth will increase and they will move through their life cycle faster. But it the temperature can be too high for others, so their metabolic reactions slow down
  • It will also affect distribution of species, as they will move to where the conditions are ideal for them
  • Changing rainfall patterns- Will affect life cycles of some organisms amd will also affect distribution
  • Seasonal cycles- Global warming is thought to change the timing of seasons. Organisms are adapted to the timing of the seasons and the changes that happen, to a change in the timing will affect life cycles and distribution
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Reducing Global Warming

  • The movement of carbon between organisms is called the carbon cycle. Carbon in the form of CO2 is absorbed by plants through photosynthesis, and is transferred to animals eating the plants.
  • It is returned to the atmosphere through respiration of animals. When dead, organic matter can end up in the soil away from decomposers, and evenutally form fossil fuels. When combusted, they release CO2 into the atmosphere
  • To reduce global warming, we need to either reduce the amount of CO2 put into the atmosphere, or remove it from the atmosphere
  • Biofuels are carbon neutral as the CO2 released when they are burnt is conteracted by the CO2 the plants absorbs when they grow. They can be used as a alternative to fossil fuels
  • Redeforestation is the planting of new trees in forests which have been depleted. More trees means more CO2 is removed from the atmosphere by photosynthesis. It is then stored in the tree, so it is kept out of the atmosphere
  • People disagree about global warming strategies. Farmers and drivers support biofuels, consumers and conservationists oppose. Wind turbine companies and environmentalists support wind farms, local communities and bird conservationalists oppose
  • Data about global warming can be extrapolated to make predictions. This has limitations- we don't know how emissions will change, how it will be managed and changes due to natural causes
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