Blue Carbon: An Untapped Resource in Climate Change Mitigation

In 2023, we witnessed an extraordinary series of climate-related records being broken around the world. Almost 50% of the year recorded global temperatures 1.5⁰C hotter than pre-industrial levels – higher than any other year on record.[1] In Hong Kong, all twelve months were warmer than usual, making 2023 one of the second warmest years on record, with the annual mean temperature reaching 24.5°C.[2] Ice mass in Greenland and Antarctica continued to shrink, while global average sea-surface temperatures reached record highs.[3] The need for climate mitigation has never been greater. Amidst the various solutions, "blue carbon" ecosystems are emerging as a crucial yet underappreciated means of storing carbon.

Annual mean temperature in Hong Kong 1885-2023 (Image source: Hong Kong Observatory)

Ice mass changes in the Greenland and Antarctic Ice Sheets from 2022 to 2023 (Image source: NSIDC)

Blue carbon refers to the carbon captured by the world's oceanic and coastal ecosystems. Mangroves and seagrasses, for example, are particularly effective at sequestering carbon from the atmosphere, at rates 10 times greater than tropical forests and storing three to five times more carbon for similar amounts of area.[4] Blue carbon ecosystems also have great carbon storage potentials as their waterlogged soils are anaerobic, so organic matter decomposes very slowly.[5]

Global distribution of blue carbon ecosystems (Image source: The blue carbon initiative)

These ecosystems provide numerous other benefits beyond carbon sequestration, including coastal protection and water purification.[6]Mangroves, for example, are widely known as natural barriers against storm, tsunamis, waves and coastal erosion, serving as the first line of defense for coastal communities. Moreover, blue carbon ecosystems are crucial hubs for biodiversity.[7]They provide habitats for a wide variety of marine and coastal species, from birds, fish and mammals to invertebrates, algae and microbes.

Functions and services of an intact mangrove ecosystem (Image source: Akram et al.)

Despite their importance, human activities such as urbanisation, aquaculture and pollution, are threatening blue carbon ecosystems.[8] An unusually dry season induced by climate change led to the worst wildfires blazing across the world’s largest tropical wetland in Pantanal, Brazil.[9] The degradation and destruction of these ecosystems releases stored carbon back into the atmosphere, intensifying climate change. Moreover, it diminishes their capacity to serve as natural buffers, thereby making coastal areas more vulnerable.

Brazil's tropical wetlands ablaze in massive fires (Image source: Reuters)

To harness the potential of blue carbon ecosystems, it is crucial to integrate them into national and international climate strategies. Governments need to protect existing blue carbon ecosystems and restore degraded ones. We have to develop robust methodologies for measuring and monitoring blue carbon stocks and fluxes to inform policy decisions.[10]

UN World Restoration Flagship Managrove Regeneration in Sri Lanka (Image source: UNEP)

In addition, green bonds, climate funds, and sustainability-linked loans can be leveraged to channel resources towards blue carbon conservation and restoration projects.[11]By aligning the interests of investors, governments, and conservationists, green finance helps create a sustainable funding model that supports long-term ecological health and resilience, contributing to the fight against climate change.

Blue carbon ecosystems present a powerful yet underutilised tool in climate mitigation. Capturing and storing carbon more efficiently than many terrestrial ecosystems, they offer a unique opportunity to tackle climate change while enhancing biodiversity and protecting coastal communities.