Human Impacts on the Carbon Cycle (AQA A Level Geography)

Extracting hydrocarbons

• Hydrocarbons lock up carbon within the lithosphere over long periods of time
• Carbon diffuses from the atmosphere allowing phytoplankton and animal life to use the carbonate ions to form shells and skeletons 
• Upon death, they sink to the ocean floor where (over a very long time) they are compressed into oil, coal and gas
• People have extracted hydrocarbons to produce energy and heat for a long time
• But, the rate of extraction has increased over time which is moving lithospheric carbon stores to the atmosphere 
• Extractive industries (such as Canada tar sands project) are responsible for half of the Earth's carbon emissions
• Since 1970, hydrocarbon extraction has risen from 6bn tonnes to 15bn tonnes, which is three times faster despite the population only doubling since then
• Furthermore, extraction processes are destroying the environment and biodiversity is lost, thereby reducing the availability of vegetation to photosynthesise the CO2 from the atmosphere

Burning hydrocarbons

• Burning fossil fuels affects the finely balanced climate
• Since the 1960s, global concentrations of CO2 have risen from 320 ppm to just over 418 ppm (2022)
• This is the highest recorded level ever

Levels of carbon dioxide in the atmosphere remained fairly cyclical prior to the industrial revolution, when carbon dioxide levels have continued to increase, with no sign of dropping as in the past

• As CO2, methane and water vapour are released, they act as greenhouse gases and trap heat within the Earth’s atmosphere
• Anthropogenic activities are responsible for almost all of the increase in greenhouse gases in the atmosphere over the last 150 years

• 90% of global CO2 emissions come from burning fossil fuels and industry
• Emissions from coal (42%), oil (33%), gas (19%), cement (6%) and gas flaring (1%)
• Natural gas; often promoted as a cleaner energy source; accounts for a fifth of the world’s total carbon emissions

• Countries such as China and the USA dominate CO2 emissions from these sources

• Ten per cent of all released carbon is due to changes in land use
• Climate change and the short-term cycle are mainly impacted

Farming practices

• Agricultural practices release carbon either directly or indirectly
• Indirectly through burning fossil fuels to run machinery and fertilisers based on fossil fuels
• Ploughing and harvesting through disturbing the soil, burning straw stubble etc
• Slash and burn techniques for livestock rearing
• Livestock digestive processes produce methane
• 5.5 tonnes (20%) of the USA's total emission of methane, originate from cattle 
• Bacteria in the waterlogged soil of rice fields, produce methane as a bi-product
• Nitrous oxide, a very potent greenhouse gas, is also produced by soil microbes in rice fields
• The impact of these gases in the atmosphere is roughly equivalent to 1,200 coal power plants
• 50% of the world’s population relies on rice as their primary food source

Urbanisation

• Urbanisation has had and still is, having a significant impact on local carbon cycles
• Stores, such as trees, are removed; parks are replaced with housing; surfaces are replaced with concrete pavements
• Just 2 per cent of Earth’s total land area is urban but is responsible for 97% of anthropogenic CO2 emissions
• Emissions originate from transport, industry, and land development
• Cement and concrete are the key building materials in the process of urban development
• However, the chemical conversion of limestone to lime creates CO2 
• Many of the world's cities, such as London, Sydney, Rome, and Dubai, are 'defined' by their towering concrete structures 
• Globally, the cement industry contributes around 7.5% of total anthropogenic CO2 emissions
• The amount of CO2 released depends on the types of materials used in its production, the firing of limestone, along with the types of fossil fuels being burned through the various stages

If the cement industry were a country, it would be the third largest emitter in the world - behind China and the US. It contributes more CO2 than aviation fuel (2.5%) and is not far behind the global agriculture business (12%). Source: BBC News

Deforestation

• Deforestation generates 20% of global CO2 emissions 
• Undisturbed forestry is carbon neutral as any decomposition and its slow release of CO2 is compensated through the growth of new vegetation
• Burning of wood for heating or clearing woodland (slash and burn), along with wildfires immediately releases CO2 into the atmosphere
• Conversion of woodland (grass for cattle rearing) reduces the system’s ability to absorb CO2 in the future, making it a carbon source instead of a carbon sink
• Deforestation is concentrated around tropical areas for building, mining, ranching and for commercial crops such as soya and palm oil
• Timber is a valuable source of income through wood products such as furniture