Applying Crushed Rock to Croplands Reduces Atmospheric CO2, Study Finds

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A new study pub­lished in Nature sug­gests that large-scale dis­per­sion of finely crushed rocks on farm­lands can func­tion as a car­bon diox­ide reser­voir and sig­nif­i­cantly reduce the atmos­pheric amount of CO2.

The tech­nique is known as enhanced rock weath­er­ing and researchers cal­cu­late that when prop­erly deployed, it has the capac­ity to sequester up to two bil­lion tons of CO2 from the Earth’s atmos­phere each year.

The amount of CO2 removed coun­ter­bal­ances the annual emis­sions of the global avi­a­tion and ship­ping sec­tors com­bined or almost half of Europe’s annual green­house gas emis­sions.

Rock weath­er­ing can help nations meet the Paris Agreement objec­tives and limit global warm­ing to less than 2 ºC (3.6 ºF) above the pre-indus­trial lev­els, the researchers noted.

The pro­posed method requires finely grind­ing basalt vol­canic rock and other mate­ri­als from the min­ing and con­struc­tion indus­try and spread­ing the crushed rocks on arable and peren­nial crops.

Due to its min­eral chem­istry, the rock dust oper­ates as a CO2 seques­tra­tor, absorb­ing the gas from the atmos­phere. The stored car­bon diox­ide is then grad­u­ally con­verted to dis­solved inor­ganic car­bon and is removed via drainage waters.

The largest global emit­ters of green­house gases also exhibit the largest abil­ity to reduce the atmos­pheric CO2 by apply­ing the method, the study deter­mined, due to their exten­sive agri­cul­tural land.

“Carbon diox­ide draw­down strate­gies that can scale up and are com­pat­i­ble with exist­ing land uses are urgently required to com­bat cli­mate change, along­side deep and sus­tained emis­sions cuts,” David Beerling, a pro­fes­sor at the University of Sheffield in the United Kingdom and the lead author of the study, said.

“Spreading rock dust on agri­cul­tural land is a straight­for­ward, prac­ti­cal CO2 draw­down approach with the poten­tial to boost soil health and food pro­duc­tion,” he added. ​“Our analy­ses reveal the big emit­ting nations – China, the United States, India – have the great­est poten­tial to do this, empha­sis­ing their need to step up to the chal­lenge.”

In Europe, rock weath­er­ing would per­form most effec­tively in Spain and France, offer­ing the means to off­set their green­house gas emis­sions by 40 per­cent.

The cost involved to achieve a two-bil­lion ton decrease of atmos­pheric car­bon diox­ide by 2050 varies between $80 and $190 per ton of CO2 for the big emit­ters, depend­ing on the labor, fuel and elec­tric­ity costs of each coun­try.

Farmers look­ing to add agri­cul­tural lime­stone to their fields to reduce soil acid­i­fi­ca­tion are poten­tial appli­ca­tors of rock weath­er­ing and the exist­ing logis­ti­cal infra­struc­ture can accom­mo­date a fast appli­ca­tion of the method.

“The prac­tice of spread­ing crushed rock to improve soil pH is com­mon­place in many agri­cul­tural regions world­wide,” researcher Steven Banwart said. ​“The tech­nol­ogy and infra­struc­ture already exist to adapt these prac­tices to uti­lize basalt rock dust. This offers a poten­tially rapid tran­si­tion in agri­cul­tural prac­tices to help cap­ture CO2 at large scale.”

The study also spec­i­fied that the cre­ation of reg­u­la­tory and incen­tive frame­works is nec­es­sary for the method to suc­ceed and urged the gov­ern­ments to cre­ate inven­to­ries of suit­able rock mate­ri­als.

• Nature
• The University of Sheffield