1) You can't just blow them up. You have to crush the rocks into something resembling sand to get the alkalinity released in human time scales. 2) Large means

1) You can't just blow them up. You have to crush the rocks into something resembling sand to get the alkalinity released in human time scales. 2) Large means quite large. I ran a back-of-the-envelope estimate some years ago and found that the Hawaiian island [1] of Kauai could reduce atmospheric CO2 roughly back to pre-industrial levels if it were completely pulverized and weathered away down to the seafloor. That's trillions of tons of rock. 3) The benefits of curbing CO2 are shared globally, but the costs are concentrated locally. It's the same kind of prisoner's dilemma that results in e.g. people still burning billions of tons of coal each year. I think that accelerated silicate weathering is the best geoengineering option and one that's likely to be deployed at scale later this century, but it's not really going to be easy. [1] AKA "underwater mountain, with the top poking above water"