A new study published in Science uses 30 years of atmospheric oxygen and carbon dioxide measurements to separate land and ocean carbon uptake. It finds the ocean absorbed about 2.8 billion tonnes of carbon per year from 1990 to 2019, roughly 35% of fossil fuel emissions, and that this sink strengthened by 0.63 billion tonnes per decade. The land sink, by contrast, averaged around 1 billion tonnes per year and has shown no long-term increase, peaking around 2009 and declining since. The results challenge current land models that predict increasing uptake as CO2 and nitrogen stimulate plant growth. They also suggest the ocean sink is stronger than simulations show. Researchers warn that warmer seawater holds less CO2, and acidification could limit future ocean uptake, meaning these sinks are not guaranteed. For carbon markets and climate policy, the findings underscore the need for long-term atmospheric monitoring and a harder look at assumptions about land-based removals. If land sinks are stalling, offset projects and national climate targets built on those assumptions may need adjusting.
