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. 

It’s a process that occurs with or without human intervention, but on geologic time scales. 

“We need something much more rapid than what nature can muster at this point,” Rau said. 

According to estimates by the National Academies of Sciences, even if the global community meets its emissions reduction goals, by 2050 it will still need to remove an additional 10 gigatons of CO2 annually to avoid devastating climate outcomes.

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.  

Much of that fear stems from a scandal that erupted in 2012. 

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. The experiment caused a plankton bloom so large it was reportedly visible from space.   An international uproar ensued. 

While there was no evidence that the experiment did any harm, the international scientific community considered it a public relations disaster.

“It just backfired massively. So this time, I think we should be really careful to get everyone on board,” said Lennart Bach, a marine biogeochemist at the University of Tasmania in Australia. 

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. 

Oceanographer Hugh MacIntyre, who has studied phytoplankton for more than 35 years, said research is starting with the microscopic algae for a reason.

“Every organism that you see in the ocean, whether it’s an orca or a fish, a starfish, a lobster, whatever — it eats something that ate something that ate the phytoplankton,” MacIntyre, a professor at Dalhousie University, said. 

So far, 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. 

“We’re going way on the extreme because we want to know at what point would it make a difference,” he said. 

MacIntyre said he’ll never be able to definitively prove that the antacid will have no harmful effects on marine life, but he can test how the plankton fare when pushed to extremes. 

“Ultimately, the question is, at what point are you confident enough that there’s not a problem?” he said.