The Greenhouse Effect
Specification Point 8.24:
Describe how various gases in the atmosphere, including carbon dioxide, methane and water vapour, absorb heat radiated from the Earth, subsequently releasing energy which keeps the Earth warm: this is known as the greenhouse effect
- When shortwave radiation from the sun strikes the Earth’s surface it is absorbed and re-emitted from the surface of the Earth as infrared radiation.
- Much of the radiation, however, is trapped inside the Earth’s atmosphere by Greenhouse gases which can absorb and hold the radiation.
- Carbon dioxide, methane and water vapour are gases that have this effect, and although present in only small amounts, they are causing significant upset to the Earth’s natural conditions by trapping extra heat energy.
- This process is called the Greenhouse effect.
Greenhouse gases trap some of the Sun’s radiation causing the Earth to warm up
Human Activity & Climate Change
Specification Point 8.25:
Evaluate the evidence for human activity causing climate change, considering:
a) the correlation between the change in atmospheric carbon dioxide concentration, the consumption of fossil fuels and temperature change
b) the uncertainties caused by the location where these measurements are taken and historical accuracy
CO2 & Fossil Fuels
- There is a direct correlation between the amount of atmospheric carbon dioxide and fossil fuel usage and the changing temperature on Earth.
- Human population is increasing and with it the global demand for consumer goods, housing and energy which are supplied with greater and more widespread industrialization.
- 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 is 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.
- 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.
Graph showing the steady increase in atmospheric CO2 since 1700
Graph showing the steady increase in temperature from when accurate records exist
Uncertainty & Historical Accuracy
- Advancements 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 levels, which include:
- Analysis of the fossil record.
- Analysis of trapped gas bubbles and tree rings.
- The ice sheets also trap valuable samples of past atmospheric conditions.
- 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.
Edexcel GCSE Chemistry Notes
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