Oceans absorbed 35% of fossil fuel CO2 emissions from 1990 to 2019, study finds

A new study in Science used 30 years of atmospheric oxygen and CO2 measurements from Scripps Institution of Oceanography to track where fossil fuel emissions actually go. It found oceans absorbed 35% of fossil fuel CO2 between 1990 and 2019, while land ecosystems absorbed 13%. Together they took in roughly half of emissions. The ocean sink grew each decade by about 630 million metric tons per year. The land sink peaked around 2009 and has declined since. That pattern challenges climate models that expected terrestrial uptake to keep rising with CO2 levels. It also raises concerns about ocean acidification, because more CO2 in seawater lowers pH and threatens marine life. Warmer surface waters may also hold less CO2, which could weaken the ocean sink over time. For anyone tracking carbon budgets, carbon removal, or climate policy, this is a useful check on assumptions about natural sinks.