Blue carbon is a word coined by the United Nations Environment Programme (UNEP) in 2009, referring to the carbon dioxide (CO2) stored in the ocean after being absorbed by marine life such as seaweed.

Atmospheric CO2 moves into the ocean through the sea surface, but CO2 in the ocean also goes back to the atmosphere, so carbon travels back and forth between the atmosphere and the ocean. In the oceans, marine life including seaweed and mangroves absorb the CO2, and stored in the seabed.

As marine life absorbs more than half (55 percent) of CO2 absorbed by all living things globally, blue carbon has been gaining attention as an effective means of mitigating global warming.

As seaweed also absorbs nitrogen and phosphorus from domestic wastewater, it purifies water too. If the water quality is improved, the ocean will be a better habitat for fish. According to some studies, seaweed can also capture microplastics, and this suggests that seaweed has the power to mitigate multiple problems simultaneously.