In brief
Climate change has already cut the ocean's carbon sink by 6% — and the measurement systems required to compile a reliable dataset are shrinking
The ocean absorbs roughly 30% of anthropogenic CO₂ emissions and 90% of the excess heat trapped by climate change, but anthropogenic warming has already reduced its carbon sink capacity by about 6% compared with a world without climate change, according to the UNEP Copenhagen Climate Centre's Climate Technology Progress Report 2026, published ahead of COP31.
The report's most uncomfortable finding concerns measurement. Routine surface ocean CO₂ observations cover only 2% of the global ocean, seasonally biased toward summer, and the number of ship-based observations has declined in recent years despite growing recognition of their importance. Expanding coverage to 5% would significantly reduce uncertainty in sink estimates.
Against that backdrop, the report distinguishes three technology families with radically different maturity: ocean observation and digital systems (established but underfunded); blue carbon ecosystems (relatively mature and deployable, sequestering around 111 Mt C a year, but with limited mitigation potential relative to need); and marine carbon dioxide removal (low technology readiness, significant scientific and governance uncertainty). It argues each needs a differentiated, evidence-based and precautionary pathway, and proposes "Ocean Carbon Intelligence" — integrating observations, data infrastructure and models — as the enabling framework.
Governance remains fragmented across UNCLOS, the London Protocol, the CBD and the UNFCCC. The London Protocol's 2013 amendment on marine geoengineering has drawn just nine of the 37 ratifications needed to enter into force.
Funding is the binding constraint: US$13 billion over the past decade went to ocean-climate sustainability against an estimated US$550 billion needed annually.
The report sets out six priorities, from sustained observation investment to grant-based finance for Small Island Developing States, which steward 15.2% of global exclusive economic zones while producing less than 1% of global emissions.
