At the gigatonne scale, nothing is easy to store. Fill the entire Hoover dam with graphite, and you've stored 6 gigatonnes. We need to store tens of gigatonnes

At the gigatonne scale, nothing is easy to store. Fill the entire Hoover dam with graphite, and you've stored 6 gigatonnes. We need to store tens of gigatonnes per year for a hundred years.