Previously, we talked about how Earth transfers naturally produced carbon between sky, sea, and soil.

Today, scientists are working to put CO2 from fossil-fuel combustion and agriculture back into the ground rather than into the atmosphere—by mimicking Earth’s natural carbon cycle.

Capturing and compressing CO2 from the exhaust stream of, say, a coal power plant, is challenging and expensive. But when done, the gas becomes a low-density liquid.

Researchers have developed and tested methods to pump it deep underground—into depleted oil fields, coal seams, and rock formations whose small pores are filled with saltwater.

Once there, it dissolves and the saltwater becomes carbonated, less than a soft drink. Studies suggest that carbon can remain trapped in these formations indefinitely, similar to the way hydrocarbons are trapped.

While international tests of these processes have been successful, other more experimental methods are striving to turn CO2 gas into useful solid materials.

New trials have injected CO2 into volcanic basalt, where it formed carbonate minerals.

Others combine carbon and calcium, similar to the way snails and clams draw them from seawater to make their shells.

The challenges with all these methods are expense and scale. Storing enough human-produced carbon to make a difference on the climate, in the time frame needed, will not be easy.

But thanks to government and industry investment in research, we now have enough experience to begin large-scale tests.