The strategy is inspired by the natural process of chemical rock weathering, where rain - which is slightly acidic - "Weathers" or erodes the surface of rocks and minerals, and then transfers that alkalinity to the ocean via runoff.

Scientists have to walk a delicate line - design a method that's scalable and effective enough to actually affect the climate without adversely affecting the environment in the process. "People, for better or worse, perceive the oceans as pristine, and they're going to have some serious concerns about interventions of this nature," said Burns, referring to a fear in the scientific community that any negative affects or public distrust of one ocean-based carbon capture method could create backlash against all other approaches.

A Canadian company experimented with ocean fertilization by dumping 120 tons of iron-enriched dust into the ocean off the coast of British Columbia to stimulate phytoplankton growth. In an attempt to pre-empt fears over safety, Planetary is partially funding research at Dalhousie University in Nova Scotia into oyster reproduction and phytoplankton growth.

MacIntyre's tests haven't resulted in significant negative impacts to plankton growth, and he's using a concentration of magnesium hydroxide that's 10 times higher than what Planetary actually intends to use.

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