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From mangroves to seasgrasses - Carbon Capture and Storage Nature’s Way

Article by: Nick Nuttall, Spokesperson UN Environment Programme

One solution to combat climate change which has attracted significant interest from power companies and some governments in Europe, North America and Japan is carbon capture and storage.

The idea is that emissions from power stations and other sources can be captured and consigned to faults and fractures in the Earth’s surface where it can be held for thousands if not millions of years.

But there is one other way which is tried and tested and has been operating for millennia--'Blue Carbon' linked with marine ecosystems such as mangroves.

Studies estimate that carbon emissions-equal to half the annual emissions of the global transport sector-are being captured and stored by these marine ecosystems which also include salt marshes and seagrasses.

A combination of reducing deforestation on land, allied to restoring the coverage and health of these marine ecosystems could deliver up to 25% of the emissions reductions needed to avoid 'dangerous' climate change.

But a report, produced by three United Nations agencies and leading scientists warns that far from maintaining and enhancing these natural carbon sinks humanity is damaging and degrading them at an accelerating rate.

It estimates that up to seven percent of these 'blue carbon sinks' are being lost annually, or seven times the rate of loss of 50 years ago.

If more action is not taken to sustain these vital ecosystems, most may be lost within two decades argues a report called Blue Carbon: the Role of Healthy Oceans in Binding Carbon compiled by UNEP, the Food and Agriculture Organization (FAO) and the Intergovernmental Oceanographic Commission of UNESCO.

Countries are already moving forward on a UN partnership known as UN-Reduced Emissions form Deforestation and forest Degradation (UN-REDD) aimed at providing the finance for governments in developing countries conserve forests while also generating jobs in natural resource management and helping to reverse the rate of loss of biodiversity.

This is because deforestation accounts for around 17 per cent of global climate change emissions.

If the world is to decisively deal with climate change, every source of emissions and every option for reducing these should be scientifically evaluated and brought to the international community's attention-that should include all the colours of carbon including now blue carbon linked with the seas and oceans.

If governments are willing to finance conservation of forests, then perhaps one day similar support could be provided to conserve and maintain carbon-absorbing marine ecosystems.

The report points out further reasons why this should be considered:-

  • Of all the biological carbon, or green carbon captured in the world, over half (55%) is captured by marine-living organisms - not on land - hence the new term blue carbon.
  • Marine-living organisms range from plankton and bacteria to seagrasses, saltmarsh plants and mangrove forests.
  • The ocean's vegetative habitats, in particular, mangroves, salt marshes and seagrasses, cover less than 1% of the seabed.
  • These form the planet's blue carbon sinks and account for over half of all carbon storage in ocean sediment and perhaps as much as over 70%.
  • They comprise only 0.05% of the plant biomass on land, but store a comparable amount of carbon per year, and thus rank among the most intense carbon sinks on the planet.
  • Blue carbon sinks and estuaries capture and store between 235-450 Teragrams (Tg C) or 870 to 1,650 million tons of CO2 every year - or the equivalent of up to near half of the emissions from the entire global transport sector which is estimated annually at around 1,000 Tg C, or around 3,700 million tons of CO2, and rising.
  • Preventing the further loss and degradation of these ecosystems and catalyzing their recovery can contribute to offsetting 3-7% of current fossil fuel emissions (totaling 7,200 Tg C a year or around 27,000 million tons) of CO2 in two decades - over half of that projected for reducing rainforest deforestation.
  • The effect would be equivalent to at least 10% of the reductions needed to keep concentrations of CO2 in the atmosphere below 450 ppm needed to keep global warming below two degrees Celsius.
  • Combined with action under REDD, halting the degradation and restoring lost marine ecosystems might deliver up to 25% of emission reductions needed to keep global warming below two degrees Celsius.
  • Unlike carbon capture and storage on land, where the carbon may be locked away for decades or centuries, that stored in the oceans remains for millennia.

Currently, on average, between 2-7% of our blue carbon sinks are lost annually, a seven-fold increase compared to only half a century ago.

  • In parts of southeast Asia losses of mangroves since the 1940s are as high as 90%.
  • Large-scale restoration of mangroves has been successfully achieved in Vietnam's Mekong Delta and salt-marsh restoration in Europe and the United States.

Countries with extensive, shallow coastal areas that could consider enhancing marine carbon sinks include India; many countries in southeast Asia; those on the Black Sea; in West Africa, the Caribbean, the Mediterranean, eastern United States and Russia.

And there are other reasons to conserve these marine ecosystems and realize multiple, Green Economy benefits.

Coastal waters account for just seven percent of the total area of the ocean. However, the productivity of ecosystems such as coral reefs, and these blue carbon sinks mean that this small area forms the basis of the world's primary fishing grounds, supplying an estimated 50% of the world's fisheries.

They provide vital nutrition for close to three billion people, as well as 50% of animal protein and minerals to 400 million people of the least developed countries in the world.

The coastal zones, of which these blue carbon sinks are central for productivity, deliver a wide range of benefits to human society. These include filtering water, reducing effects of coastal pollution, nutrient loading, sedimentation, protecting the coast from erosion and buffering the effects of extreme weather events.

  • Coastal ecosystem services have been estimated to be worth over US$25,000 billion annually, ranking among the most economically valuable of all ecosystems.
  • Much of the degradation of these ecosystems not only comes from unsustainable natural resource use practices, but also from poor watershed management, poor coastal development practices and poor waste management.
  • The protection and restoration of coastal zones, through coordinated integrated management would also have significant and multiple benefits for health, labour productivity and food security of communities in these areas.

Some countries are moving to grasp the climate and other opportunities represented by marine ecosystems. Eye on Earth, an initiative of organizations including the Environment Agency-Abu Dhabi; AGEDI and UNEP—has included Blue Carbon as one of its special initiatives aimed at providing maps and data on where such ecosystems can be found in countries and communities.

Marine ecosystems already provided humanity with extraordinary services and economic benefits—from tourism to fisheries: perhaps it is time to recognize the carbon capture and storage value as one way of cost effectively combating climate change.

Blue Carbon - The Role of Healthy Oceans in Binding Carbon can be accessed at or at, including high and low resolution graphics for free use in publications

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