Human Impacts on the Carbon Cycle (HL IB ESS OLD COURSE - IGNORE)
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
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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