Carbon ‘rock fix’ impractical: study


Claims that global warming can be braked by dissolving huge quantities of rock in the sea to absorb carbon emissions are laden with flaws, a study argues.

The analysis is the latest scientific appraisal into geo-engineering, or techniques that are being promoted as quick fixes to the growing climate crisis. Scientists in Germany probed the feasibility of “enhanced weathering,” using a scenario in which a plentiful magnesium silicate rock called olivine would be crushed and scattered into the oceans.

Doing so would make the waters more alkaline and thus better able to absorb man-made carbon dioxide emissions from the air.

The oceans are a massive carbon “sink,” having absorbed roughly half of the fossil-fuel gases humans have emitted, according to researchers. But this spongelike ability is thought to be in worrying decline. As a result, comparatively more heat-trapping gases are entering the atmosphere and the oceans themselves are becoming more acidic, threatening many species.

Writing in the British journal Environment Research Letters, scientists at the Alfred Wegener Institute for Polar and Marine Research in the German town of Bremerhaven calculated that if 3 billion tons of olivine were deposited into the oceans every year, it would compensate for only around 9 percent of present carbon dioxide emissions. And nearly a third of those emissions would indirectly return to the atmosphere because of the energy costs of grinding the rock to a diameter of around 1 micrometer — about 10 times finer than a grain of talcum powder — so that it could dissolve.

There might also be a shift in the fundamental marine ecosystem, as one species of phytoplankton benefiting from the chemical change in the sea wins out against another, the study points out.

The findings are based on lab research into the carbon dioxide absorption abilities of olivine, which were then factored into a powerful U.S. model for ocean circulation.

“If this method of geo-engineering was deployed, we would need an industry the size of the present-day coal industry to obtain the necessary amounts of olivine,” lead author Peter Koehler said. “To distribute this, we estimate that 100 dedicated large ships with a commitment to distribute 1 gigaton of olivine per year would be needed.

“Taking all our conclusions together — mainly the energy costs of the processing line and the projected potential impact on marine biology — we assess this approach as rather inefficient. It certainly is not a simple solution against the global warming problem,” Koehler said.