Climate change causes many types of damage, from heatwaves to floods. To measure these damages, economists use a number called the social cost of carbon. This value estimates how much harm is caused by releasing one extra tonne of carbon dioxide into the atmosphere. Governments use it to guide climate policies, such as carbon taxes or emission limits. However, a new study published in Nature Climate Change shows that this cost has been seriously underestimated because it has ignored the ocean.
The ocean plays a vital role in supporting life and the global economy. It provides food through fisheries and aquaculture, protects coastlines with ecosystems like mangroves and coral reefs, and supports trade through ports and shipping. Scientists call these benefits “blue capital.” Until now, most economic models have focused mainly on land-based impacts of climate change and have not fully included damage to ocean systems.
The researchers combined new ocean science with economic models to estimate how climate change affects key ocean-related systems. These include coral reefs damaged by warming and acidification, mangroves threatened by rising seas, fish populations changing due to warmer waters, and ports at risk from stronger storms and sea-level rise. All of these impacts reduce human well-being and cause economic losses.
When the researchers included these ocean impacts, they found that the social cost of carbon almost doubled. For the year 2020, the ocean-related damages alone added about 48 US dollars per tonne of carbon dioxide. This is on top of existing estimates that already include land-based damages. When a lower discount rate was used—giving more weight to future generations—the cost increased even more, reaching as high as 168 US dollars per tonne.
These findings have major implications for climate policy. If governments continue to ignore ocean damage, they may set carbon prices that are too low and fail to protect critical marine systems. The study also highlights fairness issues, as many coastal and low-income countries depend heavily on ocean resources and are more vulnerable to climate impacts.
In short, the ocean is not just a background player in climate change—it is central to the problem. By accounting for ocean damage, this research shows that climate change is far more costly than previously thought. Stronger and faster action to reduce carbon emissions is not only better for the planet, but also makes economic sense.
Editor of Daily 27.
Predoctoral researcher at the Department of Sociology in University of Barcelona.