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Oceans: our allies against climate change

How marine ecosystems help preserve our world


05 Oct 2017

It is well known that forests, especially rainforests, are key allies in our fight against climate change as they absorb greenhouse gas emissions. But did you know that oceans are the earth’s main buffer against climate change? In fact, about 25 percent of the greenhouse gases that we emit actually gets absorbed by the oceans, as does over 90 percent of the extra heat produced by human-induced climate change.

However, oceans are also one of the most affected by it. Human activities are resulting in acidification and increasing water temperatures that are changing our oceans and the plant and animal life within them.

Coral reefs and coastal environments in tropical regions, including mangroves and salt marshes, are in particular danger. These ecosystems store much of the carbon, which then remains in the oceans for hundreds of years, and are thus one of our “allies” against climate change. However, since the 1940s, over 30 percent of mangroves, close to 25 percent of salt marshes and over 30 percent of seagrass meadows have been lost. Right when we need them the most, we are losing these crucial ecosystems.

Here are 5 ways the oceans help fight climate change and its effects:

1. Trapping carbon: Mangroves, coral reefs, salt marshes and seagrasses make up just 1 percent of the ocean’s seabed, but they contain between 50-70 percent of the carbon stored in the oceans. Like forests, marine ecosystems take greenhouse gases out of the atmosphere and trap them, some of it for thousands of years. As such, these ecosystems are known as “blue carbon sinks.”  

2. Reducing coastal erosion: Overtime, waves carry away sediment from the shore. When this happens more quickly or forcefully, for example because of large storms, it has the potential of causing major damage to homes and coastal infrastructure. Sea grasses may look like our grass fields on land, but they are actually flowering plants that live in the salty environments of the sea floor and help hold sediment in place. Salt marshes, mangroves and coral reefs also help in slowing erosion and protecting shorelines.  

3. Protecting marine life and biodiversity:
Coral reefs occupy less than 0.1 percent of the world's ocean surface, yet they provide a home for at least 25 percent of all marine biodiversity. Often popular tourist attractions, coral reefs are the least secret of the ocean’s secret weapons. They draw people in to observe the wealth of marine life that they host. However, coral reefs are delicate ecosystems that are increasingly strained by human activity. Careless tourism, water pollution, overfishing, rising temperature and acidity are all damaging these ecosystems, sometimes beyond repair.

 4. Forming barriers to storms: Mangroves, salt-tolerant shrubs or small trees that grow in saline water of coastal areas, create barriers to destructive waves and hold sediments in place with their underwater root systems. This protects coastal communities in times of cyclones or other tropical storms. In fact, scientists concluded that mangroves could have reduced the damages caused by the 2008 Nargis cyclone in Myanmar, where parts of the coastline had lost up to 50 percent of its mangrove cover.

5. Slowing down destructive waves: Salt marshes are coastal wetlands that are flooded and drained by salt water brought in by the tides. Salt marshes are well-known for protecting the coast from soil erosion. However, they are also an effective defence against storm surges and devastating waves. Salt marshes can reduce wave sizes by up to 20 percent. As the waves move through and around these marshes, the vegetation quells the force of the water and buffers the effects of these waves on coastal communities. Once viewed as wastelands, salt marshes can rival tropical rainforests in terms of biologically productive habitats, as they serve as nurseries and refuges for a wide variety of marine life.

FAO is working to raise awareness about the importance of our oceans and to collaborate with governments, NGOs, and other partners, including coastal communities and fishers, to understand the impacts of climate change and minimise the risks to these marine environments. This, in turn, protects these coastal communities and their livelihoods, especially in Small Island Development States, which are disproportionately impacted by climate change and related extreme weather events.

We all have a role to play in protecting these habitats. Check out our Guide to the Ocean for more information. 

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