The dangers of Blue Carbon offsets: from hot air to hot water?

COP23 briefing – There has been much talk of “Blue Carbon” in the Bonn climate negotiations. But what does it really mean? This briefing sets out the issues and finds that the use of blue carbon to offset and hence effectively avoid required emission reductions in other sectors would undermine our ability to limit temperature rise to 1.5°C.

Date16 November 2017
Mangroves ©lohasteru CC BY-NC-ND 2.0

Full briefing


The use of blue carbon to offset and hence effectively avoid required emission reductions in other sectors such as fossil fuel combustion, industry, agriculture, international aviation and marine activities would undermine our ability to limit temperature rise to 1.5°C. There is very little room for offsetting in mitigation pathways compatible with the Paris Agreement due to the very limited carbon budget, yet there are already attempts to use the land sector and now the coastal ecosystems to contribute to national mitigation targets and reduce the emissions reductions needed in other sectors. This is particularly concerning for coastal ecosystems as carbon measurements are highly uncertain and carbon sequestration may, or is even likely to, be reversed by the increasing impacts of climate change.

Key points

  • Blue Carbon is a term that refers to the carbon sequestered in coastal ecosystems – namely mangroves, sea grasses and salt marshes. Large areas of these ecosystems have already been deforested or degraded by human activities leading to carbon emissions.
  • The conservation and restoration of coastal ecosystems is essential for the preservation of their essential ecosystem services, which range from supporting fisheries to providing coastal protection to carbon sequestration. In addition, healthy ecosystems tend to be much more resilient to the impacts of climate change.
  • The challenge with Blue Carbon is that the term focuses on the climate sequestration component of coastal ecosystems within a mitigation context. This is problematic for a number of reasons: Carbon flows within the highly variable environmental in the coastal zone are very difficult to measure, particularly in developing countries, so estimates of carbon sequestration are highly uncertain. In addition, it is very difficult to determine which emissions and removals are natural and which are anthropogenic.
  • The impacts of climate change and other stressors (both human and natural) can damage coastal ecosystems and may reduce their resilience in the long-term, leading to a reversal of carbon sequestration.
  • flows using Blue Carbon to achieve national mitigation targets risks diluting mitigation ambition in other sectors. Lessons from the land-use and forestry sector show how countries have already used imaginative accounting schemes to allow countries to offset their fossil fuel emissions. There is very little room for such offsetting in mitigation pathways compatible with 1.5°C, especially since Blue Carbon offsets come with high uncertainties and risks of reversal, and because their additionality (i.e. whether emissions reductions or removals would have happened without the Blue Carbon project) can be difficult to prove.
  • Any attempts to measure and set targets for carbon sequestration in coastal ecosystems should be kept separate from emissions targets in other sectors. Lessons from LULUCF have shown that integrating nature-based mitigation offsets under national mitigation targets creates loopholes, hot air, and MRV challenges. A more verifiable option would be to set targets for, for example, reducing deforestation and degradation rates, or protecting or restoring a certain area of coastal land.
  • It is essential to prevent the degradation of coastal ecosystems, but carbon sequestration is not necessarily the most valuable ecosystem service for local populations. The wealth of potential co-benefits from coastal ecosystem conservation and restoration, beyond carbon sequestration, are justification enough for schemes to incentivise their protection (e.g. Payment for Ecosystem Services, or PES) in developing countries. If well managed, such schemes could have substantial adaptation benefits for local communities, in addition to other ecosystem services. To maximise these benefits, schemes should be designed with the full set of ecosystem services in mind, not just carbon sequestration.

More information on climate change impacts on ocean ecosystems in this briefing:

“Because the Ocean” – achieving the Paris Agreement 1.5°C temperature limit