Scientific Frontline: Extended "At a Glance" Summary: Global Carbon Sink Dynamics
The Core Concept: A recent analysis reveals that the ocean's capacity to absorb atmospheric carbon dioxide is steadily increasing, whereas the net carbon uptake by terrestrial ecosystems has remained stagnant for over three decades. The ocean is increasingly serving as the planet's primary mechanism for sequestering anthropogenic carbon emissions.
Key Distinction/Mechanism: Researchers distinguished between marine and terrestrial carbon absorption by tracking highly precise atmospheric oxygen and carbon dioxide measurements, allowing them to isolate the distinct sequestration rates of each environment over a 30-year period.
Origin/History: Published in Science in November 2026 by an international team led by the Scripps Institution of Oceanography and the University of Exeter, the study analyzed atmospheric data collected between 1990 and 2019 to evaluate long-term carbon cycle trends.
Major Frameworks/Components:
- The ocean absorbed an average of 2.8 billion metric tons of carbon annually between 1990 and 2019, strengthening by roughly 0.63 billion metric tons per decade.
- The net land carbon sink absorbed roughly one billion metric tons annually during the same timeframe but peaked around 2009 and has generally declined since, contradicting predictive models that assumed rising carbon dioxide and nitrogen would persistently stimulate plant growth.
- The ocean's future sequestration capacity is threatened by climate change; warmer seawater holds less carbon dioxide and reduces deep-ocean mixing, while continuous carbon absorption lowers the pH and drives ocean acidification.
Branches of Science: Oceanography, Climatology, Biogeochemistry, Atmospheric Chemistry, and Terrestrial Ecology.
Future Application: These findings will be utilized to recalibrate global climate models, improving the accuracy of future carbon cycle predictions and guiding international climate policy regarding land-use management and emissions reduction targets.
Why It Matters: The stagnation of the terrestrial carbon sink indicates a dangerous over-reliance on the oceans to mitigate anthropogenic climate change. This highlights critical flaws in current predictive models and emphasizes the urgent need to stabilize atmospheric emissions before marine carbon sequestration reaches its thermodynamic limit.
A recent study indicates the ocean is absorbing more carbon dioxide, while the amount taken up by terrestrial ecosystems has remained unchanged for over 30 years.
The findings raise questions about the future capacity of land to absorb carbon dioxide and underline the growing importance of the oceans in regulating the global carbon cycle through "sinks," or the net uptake from the atmosphere.
The international study, led by researchers at the Scripps Institution of Oceanography at the University of California, San Diego, and co-authored by scientists from the University of Exeter, uses more than 30 years of atmospheric oxygen and carbon dioxide measurements to distinguish between the amounts of carbon absorbed by land and ocean.
The researchers determined that the ocean absorbed an average of 2.8 billion metric tons of carbon annually between 1990 and 2019, equivalent to approximately 35 percent of fossil fuel emissions over that period. The ocean carbon sink strengthened by approximately 0.63 billion metric tons of carbon per decade.
By contrast, the net land carbon sink showed no notable long-term increase. Land ecosystems absorbed an average of around one billion metric tons of carbon each year over the same period, equivalent to approximately 13 percent of fossil fuel emissions. The land sink peaked around 2009 and has generally declined since.
The results show that the ocean sink has strengthened substantially more than represented in current model simulations, suggesting that scientists still lack a complete understanding of how the carbon cycle will behave under future climate change.
The lack of growth in the net land sink also challenges many existing land models, which predict increasing carbon uptake as rising atmospheric carbon dioxide and nitrogen stimulate plant growth. The researchers note that the observed trend is particularly striking given that current estimates suggest emissions from deforestation and other land-use changes have been declining.
Professor Andrew Watson, one of the Exeter researchers, said, "Atmospheric oxygen measurements at the parts-per-million precision needed for this work are incredibly difficult to do, but the payoff is a unique understanding of the workings of the whole Earth system and how it is responding to human-caused change. These results represent decades of work by a small community of very dedicated scientists who make those observations."
While the ocean has taken up increasing amounts of carbon dioxide, its future capacity to do so may also be affected by climate change. Warmer seawater holds less carbon dioxide, while warmer surface waters are less efficient at mixing into the deep ocean, where carbon can remain stored for many hundreds of years. The absorption of carbon dioxide also lowers the pH of seawater, contributing to ocean acidification.
The findings highlight the critical role of long-term atmospheric and oceanic measurements in modeling the global carbon cycle and its response to climate change.
Funding: The research was supported by the US National Science Foundation, the National Oceanic and Atmospheric Administration, and Schmidt Sciences. Additional support for the University of Exeter researchers was provided by the European Union's OceanICU project and UK Research and Innovation.
Published in journal: Science
Authors: Eric J. Morgan, Yuming Jin, Elena Kozlova, Andrew J. Watson, Andrew C. Manning, Sönke Zaehle, Yasunori Tohjima, Xin Lan, and Ralph F. Keeling
Source/Credit: University of Exeter | Duncan Sandes
Edited by: Scientific Frontline
Reference Number: ocn111226_01
