Human Impacts on the Carbon Cycle (DP IB Environmental Systems & Societies (ESS))

Human Impacts on the Carbon Cycle

Fossil fuels

• Fossil fuels like coal, oil and natural gas are stores of carbon with virtually unlimited residence times

• Fossil fuels were formed when past ecosystems acted as carbon sinks, trapping organic carbon over millions of years

  • They were created from ancient plants and animals that lived millions of years ago

  • Over time, their remains got buried deep underground

  • As they were buried, pressure and heat turned them into fossil fuels

• Humans burn fossil fuels for energy production

  • When burned, these fuels release heat energy

  • The heat energy can be harnessed to generate electricity, power vehicles, heat buildings and fuel industrial processes

• When burned, fossil fuels become carbon sources, releasing stored carbon back into the atmosphere as carbon dioxide

Agricultural systems

• Agricultural systems can act as carbon sinks or carbon sources depending on the type of agricultural and the management techniques used:

  • Carbon sinks: regenerative agriculture techniques like crop rotation, cover cropping, and no-till farming result in soil acting as a carbon sink

    • This is because these methods increase the amount of organic matter in the soil

  • Carbon sources: drainage of wetlands, monoculture farming and intensive tillage result in soil acting as a carbon source

    • This is because these methods increase the release of carbon from soils

• Longer-term cropping practices, such as timber production, also affect carbon cycling and storage in ecosystems

  • When forests are managed sustainably for timber production, they can act as significant carbon sinks

    • This is because they sequester carbon dioxide from the atmosphere through photosynthesis and store it in woody biomass and soil organic matter

  • However, if forests are clear-cut or managed unsustainably, they can become carbon sources

    • This is because stored carbon is released back into the atmosphere (when the harvested wood is burned) quicker than it is stored in new tree growth

Oceanic carbon dynamics

• Carbon dioxide is absorbed into oceans by dissolving in sea water

  • It can also come out of the solution and is released as a gas when conditions change (e.g. when ocean temperature increases)

• Normally, oceans act as a significant carbon sink, absorbing CO₂ from the atmosphere and helping to regulate atmospheric carbon levels

  • However, the burning of fossil fuels by humans is releasing CO₂ at a faster rate than oceans can absorb

    • This is leading to rising CO₂ levels in the atmosphere

  • In addition to warming ocean temperatures caused by human-induced climate change, this is reducing the ability of oceans to act as carbon sinks

Ocean acidification

• Increased concentrations of dissolved CO₂ in oceans lowers the pH of the sea water, leading to ocean acidification

• This is causing threats to marine organisms:

  • Small decreases in ocean pH reduce calcium carbonate deposition in mollusc shells and coral skeletons

  • This can lead to weakened shells, increased vulnerability to predators and smaller and less diverse reef structures