Summary
Highlights
The carbon cycle involves the movement of carbon-containing molecules like carbon dioxide, glucose, and methane between sources and sinks. Some steps in the carbon cycle are very quick, such as fossil fuel combustion, while others are very slow, like the sedimentation and burial of organic matter into fossil fuels, which can take millions of years.
Carbon sinks are reservoirs that store more carbon than they release, helping to mitigate climate change. Examples include algae and sediments in the ocean, and plants and soil on land. Carbon sources release more carbon than they store, increasing atmospheric carbon dioxide. These include fossil fuel combustion, animal agriculture (due to methane release), and deforestation.
Photosynthesis, carried out by plants, algae, and phytoplankton, removes carbon dioxide from the atmosphere to produce glucose, acting as a carbon sink. Cellular respiration, performed by all living things, breaks down glucose to release energy and carbon dioxide, acting as a carbon source. These two processes happen quickly and balance each other out, leading to no net increase in atmospheric carbon in the short term.
Direct exchange allows carbon dioxide to move quickly and relatively equally between the ocean and the atmosphere. However, increased atmospheric CO2 due to human activity leads to more CO2 dissolving into the ocean, contributing to ocean acidification. Algae, phytoplankton, and marine organisms that form shells (calcium carbonate) also take CO2 out of the ocean, acting as carbon sinks.
Sedimentation occurs when marine organisms die and their remains sink, forming sediments. Burial is the long-term process (thousands to millions of years) where these sediments are compressed by overlying water and rock layers to form sedimentary rock or fossil fuels (coal, oil, natural gas). These represent long-term carbon reservoirs due to the extensive time they take to form.
Extraction is the mining of buried fossil fuels, and combustion is their burning for energy, which releases large amounts of CO2 into the atmosphere. The critical issue is that while burial takes millions of years, extraction and combustion happen very quickly, releasing CO2 much faster than it is naturally removed. This imbalance significantly increases atmospheric CO2, causing global warming and climate change.