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The economic toll of climate change has been substantially underestimated, according to new research, because a critical component has been overlooked: the ocean. The social cost of carbon (SCC) – an estimate of the economic damage caused by emitting one additional tonne of carbon dioxide into the atmosphere in a given year – is widely used to inform climate policy and carbon pricing. Most estimates have focused on impacts on land and those that can be easily measured in economic terms; by contrast, ocean-related damages spanning ecosystems, infrastructure and human health have remained largely absent from standard models.
Bernardo Bastien-Olvera, from the Scripps Institution of Oceanography, USA, and colleagues combined recent ocean science with economic analysis to estimate what they call an ocean-based or “blue” SCC. Their approach accounts for climate impacts on coral reefs, mangroves, fisheries and global ports, as well as wider losses to human wellbeing linked to declining marine ecosystems. By translating physical climate impacts into economic losses, the researchers capture both direct effects, such as reduced fisheries productivity or port disruptions, and wider societal impacts, including nutrition, health and biodiversity loss.
Under a high-emissions, business-as-usual scenario, the ocean component alone adds an estimated US$48 per tonne of CO₂ to the social cost of carbon, nearly doubling existing estimates. The authors calculate that including ocean damages raises the SCC from approximately US$51 per tonne of CO₂ to roughly US$97 – a 91% increase.
A striking result is the prominence of fisheries-related health effects, which account for a large share of total ocean damages. In many low-income and island nations, fish provide essential protein and micronutrients; climate-driven declines in fish stocks can therefore translate into poorer health and increased mortality. Coral reefs also emerge as major contributors to projected losses, reflecting their vulnerability to warming and acidification and the high economic value of the services they provide, from tourism to coastal protection.
The researchers find that ocean-related damages are unevenly distributed, disproportionately affecting countries most reliant on marine resources. Lower-income countries and small island developing states, where marine ecosystems underpin food security, tourism and transport, face the greatest welfare losses of 20–30%.
Against the backdrop of 41.6 billion tonnes of global CO₂ emissions in 2024, the authors estimate that ocean-related damages amount to nearly US$2 trillion in a single year, costs largely absent from current climate accounting. Looking ahead to 2100, the researchers project that market damages could reach US$1.66 trillion annually, underscoring the growing economic risks of ocean change.
Hannah Bird
Details
Nat. Clim. Chang., 2026; doi.org/10.1038/s41558-025-02533-5
