Reversing ocean acidification caused by increased carbon dioxide emissions from human activities could take centuries, according to a study published online this week in Nature Climate Change. The study suggests even removal from the atmosphere of 2.5 times the current annual emissions of CO2 per year until 2700 would not re-establish preindustrial conditions or a low-emissions state.
Sabine Mathesius and colleagues used computer models to simulate the effects of carbon dioxide removal (CDR) on the marine environment. They considered both a substantial scheme involving the extraction of up to 5 gigatonnes of carbon per year (equivalent to about half of today’s annual emissions), and a much more aggressive and probably unfeasible intervention with a maximum extraction rate of 25 gigatonnes of carbon per year.
The authors find that only on the timescale of many human generations, perhaps even millennia, could even aggressive CDR undo the effects of high emissions under a ‘business as usual’ high emissions scenario. Meanwhile, the researchers point out, perturbations in acidity, temperature and oxygen availability would most likely put marine ecosystems and the species they support at untold risk. Mathesius and colleagues conclude that immediate and ambitious action to reduce CO2 emissions is the most reliable strategy for avoiding large-scale threats to marine ecosystems.
In an accompanying News & Views, Richard Matear and Andrew Lenton write, “Simply put, once the carbon has entered the ocean it cannot be easily extracted; avoiding the carbon emissions [as CO2] in the first place is a much more effective option.”