AQA GCSE Chemistry

Revision Notes

9.2.2 Humanity & Greenhouse Gases

Human Activity & Climate Change

  • Human population is increasing and with it the global demand for food, water, consumer goods, housing and energy which are supplied with greater and more widespread industrialization
  • This creates more waste so more landfill sites are needed which increases the amount of methane by decomposition
  • The increased energy demands are met in most cases by the burning of fossil fuels which produces CO2:

Fossil fuel + oxygen → energy + H2O + CO2

  • Added to this is the effect of deforestation on the amount of CO2 as large areas of forested land are being destroyed for building and agricultural activities
  • Plants and trees remove CO2 during photosynthesis:

6CO2 + 6H2O → C6H12O6 + 6O2

  • Hence their removal increases the amount of atmospheric CO2 as there are less plants available to remove it during photosynthesis
  • Increasing agricultural activities also cause an increase in methane production
  • By analysis of the percentage of CO2 in the atmosphere and the changes in temperature over several hundred years, the evidence for the effects of CO2 on global temperature is convincing
  • There is a clear correlation between both factors as shown in the graph below.

Climate Change - Graph CO2 Evolution, IGCSE & GCSE Chemistry revision notes

Graph showing the steady increase in atmospheric CO2 since 1700

Climate Change - Graph Temperature Evolution, IGCSE & GCSE Chemistry revision notes

Graph showing the steady increase in temperature from when accurate records exist

Uncertainty & Historical Error

  • Advances in science and technology mean current levels of CO2 and global temperatures can be determined with a high degree of accuracy
  • Historical data is much less accurate due to the lack of accurate instrumentation and methods
  • Fewer locations would also have been measured due to the lack of satellites and transport
  • There are some methods to estimate past climate conditions, which include:
    • Analysis of the fossil record and tree rings
    • Analysis of gas bubbles trapped in ice from hundreds of thousands of years ago
  • Unfortunately, these methods, while providing at least some data, are not as precise as modern day techniques nor do they provide data which is representative on a global scale
  • The complexity of the Earth’s climate and contributing factors make it a difficult task to produce a working model that clearly shows the link between global warming and greenhouse gases
  • This and other difficulties have led to hype and speculation in the media in recent times in which some scientists have cast doubts on human activity and climate change
  • However, academic surveys have shown that about 97% of climate scientists do believe human activity is causing climate change

Exam Tip

It is important that peer review of research results as well as communication to a wide range of audiences is carried out to dispell myths and misinformation about climate change

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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