Discovery: An ambitious plan to slow global warming by locking CO2 deep in the ocean has hit a stumbling block, according to a new study that shows the geoengineering technique is not as effective as scientists had previously hoped. “The amount of carbon dioxide that could be taken up is less than we assumed,” said Victor Smetacek, a scientist at Alfred Wegener Institute who co-led the expedition. Don’t discount ocean fertilization yet however, say scientists working both inside and outside the …