Top 10 facts about Oceans

1. The oceans cover about 70 percent of the planet's surface

The ocean is vast and on average about 4,000 metres deep. It contains 1.3 billion cubic kilometres of water – that’s 97% of all the water on the surface of the Earth.^[1]

2. The ocean is incredibly biodiverse

Home to over 240,000 known species with millions more believed to be undiscovered ^[2,3] - as much of the deep sea, where there is no light, is still unexplored and some scientists believe it could be home to two million undiscovered species! 

Most life in the ocean we can't see with the naked eye. In addition to the microscopic bacteria and other microbes are plankton - tiny plants (phytoplankton) and animals (zooplankton) that drift with the ocean currents. Just one litre of water from the ocean can hold up to 38,000 kinds of microbes. ^[4]

3. The ocean provides around half of the Earth’s oxygen

It doesn’t just provide the air we breathe; oceans absorb over a quarter of human-induced carbon emissions and has a tremendous ability to store heat, making it a vital life support system. Our oceans have absorbed 90% of the warming that has occurred in recent decades due to increasing greenhouse gases, and the top few metres of the ocean store as much heat as Earth's entire atmosphere.^[5,6]

4. Coral reefs, mangroves, seagrasses, and saltmarshes are natural coastline barriers

They buffer shorelines against 97% of the energy from waves, storms and floods, helping to prevent loss of life, property damage, and erosion.^[7] By absorbing some of the storm’s energy, they can help reduce damage from extreme weather events like cyclones.^[8]

5. Sea water contains about 3.5% salt

But what makes our oceans so salty? Carbon dioxide in the air dissolves into rainwater, making it slightly acidic. When rain falls, it erodes rocks, releasing mineral salts that separate into ions. These ions are carried by rivers and streams to ultimately reach the ocean.^[9] Coupled with underwater volcanoes and hydrothermal vents, which directly release minerals into the ocean.^[10]

6. Melting sea ice caused by climate change affects ocean currents

Adding freshwater to the ocean decreases the saltiness of the sea, which, coupled with increased temperatures, disrupts the ocean currents that move important nutrients around the world. This can affect weather, for example, the UK is comparatively mild because of the heat brought by an ocean current from the Gulf of Mexico. Melting Arctic glaciers is weakening this current, meaning the UK could face more extreme weather.^[11]

7. The ocean is a human product highway

Around 90% of goods used around the world are transported across the oceans, with over 200 million shipping containers moved around the globe each year.^[12] This results in a wide range of environmental pressures, such as noise pollution and collisions that affect whale populations.^[13] Shipping is also a major contributor to carbon emissions and could potentially account for up to 17% of global emissions by 2050, if the sector doesn't adopt greener practices.^[14]

8. In the last 40 years we have lost an estimated 50% of our coral reefs

In the Great Barrier Reef, rising sea temperatures and ecosystem degradation have led to mass coral bleaching events in 1998, 2002, 2016, 2017, 2020, 2022 and 2024. If the average global temperature rises by 1.5°C, the estimated loss of tropical coral reefs globally is 70% - 90%. In a world with 2°C of warming, only 1% or our tropical coral reefs will remain.^[15]

9. Plastic pollution will be with us for centuries

It's been estimated that single-use plastics account for 60-95% of plastic pollution in our oceans. If all plastic pollution stopped today, marine microplastic levels would still more than double by 2050, as the current plastic waste degrades.^[16]

10. Coastal ecosystems support people, wildlife, and the climate

Coastal ‘blue carbon’ ecosystems, or blue forests, including mangroves, seagrasses, and saltmarshes, capture carbon at a faster pace than tropical forests. Mangroves, for example, can remove up to 130 million tonnes of carbon dioxide from the atmosphere each year – equivalent to taking 28 million cars off the road for an entire year! 

Protecting and restoring these ecosystems has benefits beyond the capturing of carbon, including reduction in flooding and erosion, storm protection, increased food security, and improved livelihoods for coastal communities.^[17]