Why it matters: Microsoft’s ambitious efforts to reduce its carbon footprint include reducing emissions and removing carbon from the atmosphere. The emerging carbon capture industry is trying numerous methods. One of them involves rocks that naturally absorb the substance, but the carbon still has to go somewhere.
Microsoft has beaten a deal with Heirloom Carbon, a startup that has developed a process for using limestone to sequester carbon to combat climate change. The technology could contribute to Microsoft’s ongoing push to become carbon negative.
Limestone naturally absorbs carbon over many years, but Heirloom’s method speeds up the process. The company uses a renewable energy-powered kiln to heat crushed limestone to about 1,650 degrees Fahrenheit, separating it into carbon dioxide and calcium oxide. Adding water to the calcium oxide allows it to absorb sufficient amounts of carbon within a few days, after which Heirloom reintroduces it into the furnace to restart the cycle.
Although the technology has proven its worth, it is unclear to what maximum extent it remains cost-effective. Another problem with all carbon capture methods is the storage of the material.
Heirloom permanently buries the separated carbon underground, but other groups attempt to recycle it for practical purposes. CarbonCure has developed a process to convert carbon dioxide into a mineral for concrete. The group claims that concrete mixed with CO2, which replaces some cement, is no weaker than typical building material. Furthermore, the concrete sequesters carbon forever, even if a building constructed from it collapses or is demolished.
Regardless of the effectiveness of the limestone method, it will likely need to complement other carbon capture technologies that Microsoft is using to become carbon negative by 2030. A few years ago, the company also said that by 2050 it aims to remove all the carbon it has ever emitted since its founding in 1975.
One of the most well-known removal methods involves giant vacuum-like machines that suck carbon out of the open atmosphere. However, the equipment is expensive. Microsoft has also partnered with ocean restoration company Running Tide, which uses algae and limestone to capture CO2 in the ocean. In this technique, the materials are placed on buoys hundreds of kilometers offshore and gradually decay as they accumulate carbon. Eventually they sink to the ocean floor, where natural processes prevent the CO2 from re-entering the atmosphere for hundreds or millions of years.