THE SEA EXTENDS A HELPING HAND

The first is a bit speculative, first discussed by John Martin in 1988. Sales of fish and seaweed — byproducts of restored ocean photosynthesis — can pay for ocean restoration. Experts say that restoring about 1% of the ocean would be sufficient to remove all of the excess CO2 in our atmosphere by mid-century, while being paid for by the profits or taxes on fish and seaweed. One method, Marine Permaculture Arrays, currently being funded, in part by the Grantham Foundation, restores ocean health and grows seaweed by upwelling nutrient-rich deep seawater. Martin’s method of using minute amounts of powdered iron ore to restore depleted fisheries was politically controversial in 2012, but is now making a comeback. The methods to ensure that large amounts of CO2 are sequestered safely by these processes are being perfected; research funding, either public or private, would accelerate this development and bring us climate restoration sooner.

Although oceans store a tremendous amount of carbon, carbonate rocks such as limestone store even more. Carbon dioxide from the air or from power plant exhaust can be mineralized above ground and sold. The gas can also be pumped underground into basalt rock, which actually converts the dangerous stuff into solid limestone (calcite minerals) in just a matter of months.

Climeworks estimates the cost at scale to be $100 per ton of CO2; removing a trillion tons of CO2 this way could cost $100 trillion over 30 years. This solution is only feasible if governments pay for it; to put that in perspective, in 2017, global military spending was $1.7 trillion.

THE SYNTHETIC LIMESTONE

Aside from seafood, the market with the most potential to reach our CO2 removal goal is rocks used in construction. With the exception of water, aggregate is the most transported material on Earth. Consider the fact that, globally, we buy 50 billion tons of aggregates each year for use in concrete, asphalt, road base and buildings worldwide. Of this, 70% is limestone, a rock that is almost half CO2 by weight.

Therefore, synthetically converting CO2 to limestone makes sense from an economic standpoint and is being done now. If suppliers shifted from quarried rock to synthetic limestone made from atmospheric CO2, we could remove and sell all the excess CO2 from the atmosphere by 2050.

Scaling this up by 2030 might require $5 billion in corporate investment, but the benefit is that this solution supports itself, negating the need for government subsidies or additional taxes. The limestone is created locally where it’s used, so it becomes more cost-efficient than quarried rock by reducing high transportation costs. Synthetic limestone is cost competitive when the quarry is more than 50 miles (80 kilometers) from the user. In large cities, the material must often be shipped from quarries hundreds of miles away.