Don’t bother (Image: Design Pics/Rex Features)

Suggestions that we can dump large amounts of alkaline chemicals into the oceans to prevent their acidification seems dead in the water. A study shows it would cost trillions of dollars.

As humans spew more carbon dioxide into the atmosphere, it is taken up by the oceans, turning them increasingly acidic and threatening ecosystems around the globe.

Some have suggested a simple solution: large-scale artificial alkalisation using chemicals like quicklime. Richard Zeebe and François Paquay of the University of Hawaii in Honolulu decided to see if this was realistic.


Three-ocean problem

For this, they used a model of how carbon cycles between the atmosphere, ocean and sediment. “We envisioned this as an extremely large-scale problem,” says Paquay, “so we manipulated the alkalinity in the surface of the Atlantic, Pacific and Indian oceans.”

His team modelled the coming 500 years assuming we continue emitting greenhouse gases at roughly the same rate as we have on average over the past century. They found to counteract ocean acidification, we would have to dump about 1015 moles per year of alkalinity into the oceans for about 400 years. If quicklime were to be used, it would require 1011 tonnes and trillions of dollars per year.

What’s more, geoengineering the oceans in this way would not do anything to stop global temperatures rising – in the models, Earth’s temperature rose by about 2.5 ºC.

Ocean alkalisation is unlikely to be an economically viable geoengineering option to offset global carbon emissions, the researchers concluded in a presentation at the fall meeting of the American Geophysical Union in San Francisco, California, last week.

When this article was first posted, it incorrectly stated that the model found that about 1000 tonnes of quicklime per year would be needed