Human Impacts on the Carbon Cycle (HL IB ESS OLD COURSE - IGNORE)

Revision Note

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

Examiner Tips and Tricks

What you need to understand here is that human activities can cause particular ecological systems (such as underground fossil fuel reserves, agricultural systems or our oceans) to act as carbon sinks/stores or as carbon sources. For example, until the industrial revolution, fossil fuels have acted as a significant carbon store but we have reversed this and have turned them into a carbon source.

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