Tomasz Baranowski, Flickr

Fast facts: Oceans

A quick rundown on our planet’s ecosystems

Oceans cover 71 percent of the Earth’s surface and contain 97 percent of its water. They are also the world’s largest source of protein: more than 3 billion people rely on fisheries and other marine life as their main source of protein. Around 60 million people are employed in fisheries around the world.

However, global fisheries are in decline due to overfishing. A third of fisheries are currently being depleted more quickly than they are replenished, and subsidies are contributing to this problem. According to Oceana, improved fisheries management could help increase fishery yields by up to 40 percent. If overfishing ended now, 700 million people could enjoy a daily seafood meal by 2050.

A fisherman casts his net in West Java, Indonesia. Ricky Martin/CIFOR
A fisherman casts his net in West Java, Indonesia. Ricky Martin/CIFOR

Oceans are also threatened by pollution in the form of trash, chemicals, fertilizers and untreated sewage, as well as oil and wastewater from shipping. Fertilizers from farms and lawns pose a particular problem, as their nutrients can lead to eutrophication – the flourishing of algal blooms, which can deplete the water of oxygen, causing other marine life to suffocate.

School of fish, Krabi, Thailand
A school of fish in Krabi, Thailand. Christopher Rose, Flickr

Oceans can play an important role in mitigating climate change, as they store 50 times more carbon dioxide than the atmosphere and also regulate regional climate and weather patterns. But as carbon dioxide concentrations rise due to human activity, oceans are absorbing more carbon dioxide, causing their waters to acidify. This makes it challenging for sea creatures to breathe, grow and survive.

Phytoplankton bloom
A phytoplankton bloom in the Atlantic Ocean north of Iceland. NASA on The Commons, Flickr

Carbon dioxide emissions are also contributing to climate change, which is causing glaciers and ice sheets to melt and water to expand as it heats. This leads to sea level rise, which the Intergovernmental Panel on Climate Change in 2019 estimated could reach over a meter in the next century. Around the world, 14 percent of coral reefs have been killed in recent years due to climate change.

Seaweed off the coast of Somerset, U.K. Pete Stanton, Flickr

Our understanding of the oceans remains limited, though: less than 10 percent of the ocean has been properly mapped. The U.N., though, hopes to change this through its Decade for Ocean Science for Sustainable Development, which began in 2021.

Great Barrier Reef
Coral in Michaelmas Cay, Great Barrier Reef, Queensland, Australia. Steven dosRemedios, Flickr

Read the rest of our ‘fast facts’ series on ecosystems below.



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