Carbon sequestration refers to the capture and long-term storage of carbon in forests and soils or in the oceans, so that the build-up of carbon dioxide (one of the principal greenhouse gases) in the atmosphere will reduce or slow. Managing land and vegetation to increase carbon storage can help reduce greenhouse gas emissions.

• In terrestrial ecosystems - increasing the amount of carbon stored in vegetation and soils.
• In oceans - enhancing the net uptake of carbon from the atmosphere by the oceans, through fertilisation of phytoplankton with nutrients, and injecting CO2 to ocean depths greater than 1000 metres.
• Subsurface sequestration of carbon dioxide in underground geological repositories.

All of these options are commonly known as carbon 'sinks'. The first, increasing carbon storage in terrestrial ecosystems, is currently the focus of the most attention and is the easiest and most immediate option at the present time.