Polar blue carbon review urges protection while evidence gaps limit climate policy use

Aarhus University researchers said on 9 October that a newly published review of Arctic and Antarctic marine ecosystems identifies possible carbon stores but finds too little evidence to count many of them reliably in climate policy. The review, published in Global Change Biology on 21 September, urges protection of vulnerable habitats alongside better measurement, while warning against treating polar carbon storage as a ready-made offset.

The paper by Nadescha Zwerschke and co-authors examines ‘polar blue carbon’: carbon captured, stored or transported by marine ecosystems. It draws together existing evidence and policy questions; it does not report a newly measured carbon-saving intervention. That distinction matters for governments considering whether protection of a habitat can be credited with a measurable climate benefit.

Which polar habitats could store carbon?

The review considers Arctic salt marshes and seagrass meadows, kelp forests, phytoplankton, algae associated with sea ice, fjords, continental shelves and deep-sea sediments. These habitats and pathways differ in how carbon is produced, moved and retained. Listing them as candidates does not establish how much carbon each stores or how long it remains out of the atmosphere.

Polar regions account for about one-fifth of the global ocean, according to both the review and the Intergovernmental Panel on Climate Change. The IPCC describes polar seas as important to ocean circulation and the absorption of human-caused carbon dioxide. It also says spring phytoplankton blooms support marine food webs, while sea ice affects ocean physics, chemistry, biology and exchange with the atmosphere.

The review says Arctic salt marshes and seagrasses are already considered actionable blue-carbon habitats in the framework it discusses. Expanding macroalgal habitats at both poles remain under consideration. In Arctic fjords, biological production and sediment delivered by glaciers may help move carbon into seabed deposits. The authors say open-ocean, shelf and deep-sea processes can also be overlooked.

Why the review cautions against carbon offsets

For many polar systems, robust estimates of habitat extent, carbon stocks and long-term sequestration remain unavailable. The review identifies gaps in mapping and in understanding how production and storage respond to present and future climate conditions. It does not provide a single quantified total for durable carbon storage across polar marine ecosystems.

The authors warn against using polar blue carbon as a conventional carbon offset at this stage. They identify unresolved questions about measurement, additionality, permanence and governance. An offset would require confidence that an intervention causes a carbon benefit beyond what would otherwise happen and that the benefit lasts. The review also reports finding no published assessments of management outcomes for polar blue carbon, leaving proposed protections without measured carbon results.

Warming, sea-ice loss, erosion and human pressure could strengthen some carbon pathways while weakening others, the review says. Effects vary by habitat, so the prospect of change does not establish an overall climate-mitigation gain. These uncertainties also make it difficult to transfer evidence from familiar coastal blue-carbon systems directly to polar seas.

What the authors want policymakers to do

The authors call for more research, precautionary protection of known carbon-rich and vulnerable habitats, management that considers biodiversity alongside carbon, and clearer routes for recognizing natural carbon stores in marine policy. Their near-term emphasis is on safeguarding ecosystems and building evidence, rather than opening a new offset market. The review does not set a timetable for governments to adopt a particular framework.

‘We need to understand these systems much better—but we should not wait until all uncertainties are resolved before protecting the most vulnerable and carbon-rich habitats,’ Zwerschke said in an Aarhus University account of the paper. Her statement makes protection a precautionary recommendation, not a claim that its carbon benefit has already been measured.

Mikael Sejr, coordinator of the Polar Ocean Mitigation Potential project, said in the same account that polar blue carbon is ‘not a shortcut around reducing CO2 emissions’. He said phasing out fossil fuels remains the first priority, while protection of carbon-rich marine ecosystems could form part of a broader climate and biodiversity strategy. The open scientific question is how much carbon particular polar habitats store durably, and whether specific management measures change that outcome.