The natural weathering of rock removes CO2 from the atmosphere, but only slowly. The CO2 we've pushed into the atmosphere since the beginning of industrialisation will take thousands of years to be eliminated naturally. That's why this report about an experiment where CO2 was converted to rock over an extraordinarily short period of just 2 years is so interesting.
This is still pretty much experimental technology. For example, we haven't got a cheap way to extract CO2 from the atmosphere. Here the researchers were using waste CO2 from the geo-thermal plant, which was already concentrated and so makes the process much cheaper. Also, the process works with basalt. Does it work with other rocks? And it's costly--$17 per tonne, even with the source CO2 already concentrated. (Which suggests the lowest carbon price we need to set) And it uses a lot of water, though presumably we could use waste water. All those questions need to be answered. But what it does mean is that if we wanted to, we could start a process of removing CO2 from the atmosphere. Conveniently, if we could find a cheap process to remove ambient CO2 from the atmosphere we could do this anywhere there is basaltic rock, because the level of CO2 in the atmosphere would move to equalise over the world's surface, just as it does with emissions.
What it does not mean is that we can let up on our drive to de-carbonise our economy. This will be needed in addition to stopping using fossil fuels, and it will have to be funded by taxpayers. The 220 tonnes of CO2 the project injected into the rocks equals the annual emissions for just 12 or so people in the US or Australia. This will have to be done on a fantastic scale to make a difference. All the same, it's a first small step to getting CO2 back to safer levels.
Read more here.