Scripps study: oceans absorbed 35% of fossil CO2 emissions in 1990–2019, land 13%
Using 30+ years of atmospheric O2 and CO2 data, researchers found the ocean sink grew while the net land sink showed no robust trend. The authors say this challenges many models.
Researchers at the Scripps Institution of Oceanography (UC San Diego) analyzed more than 30 years of atmospheric oxygen (O2) and carbon dioxide (CO2) observations to estimate how much carbon the ocean and land absorbed between 1990 and 2019. The results are published in Science. The ocean and the land biosphere together absorb roughly half of fossil fuel CO2 emissions science.org
Sciencescience.orgOpen source ↗. The ocean accounted for 35% of those emissions and the net land sink for 13%.
Oxygen and CO2 as a pair
The sinks cannot be observed directly, said lead author Eric Morgan. The authors note that their evolution in time is hard to quantify because data are sparse. The method relies on how the two gases behave. Burning fossil fuels consumes atmospheric oxygen and releases CO2. On land, plants take up CO2 in photosynthesis and release oxygen. Ocean uptake occurs mainly through reactions in seawater that do not affect oxygen levels. Tracking both gases therefore lets the researchers separate the ocean contribution from the land one.
The record comes from the Scripps O2 Program, launched in 1989. It measures atmospheric oxygen in air samples collected at stations along the Pacific, from the high Arctic to the South Pole. Co-author Ralph Keeling noted that such measurements are hard to sustain year after year.
Ocean sink grew, land sink did not
The ocean carbon sink increased by 0.63 ± 0.19 petagrams of carbon per year per decade (Pg C year−1 decade−1). Its mean over the period was 2.8 ± 0.4 Pg C year−1 science.org
Sciencescience.orgOpen source ↗. The net land sink showed no robust trend, with a mean of 1.0 ± 0.5 Pg C year−1, despite large decadal variability.
Morgan called it surprising that the net land sink has not kept pace with rising CO2 levels and said the land sink may be fragile. The authors report that the results challenge many process-based model simulations of the land and ocean sinks. They say this questions the ability of those models to predict future climate states accurately.
Ocean uptake of CO2 also lowers the pH of seawater, making it more acidic.
