Note that there's a bit of a problem with fertilizing the oceans with iron (the other strategy mentioned in the article) to cause phytoplankton blooms which the

Note that there's a bit of a problem with fertilizing the oceans with iron (the other strategy mentioned in the article) to cause phytoplankton blooms which then sink to the seabed, thus removing carbon from the atmosphere. It's that microbes in the water column steadily break down sinking biomass, sucking down free oxygen levels as they do so. This results in large zones of anoxic bottom water, or at least hypoxic, aka 'dead zones' as in the Gulf of Mexico. These zones were much more widespread 100 million years ago when many oil and gas-bearing sediments were being laid down, but turning much of our modern ocean into a sulfurous stinking anoxic zone is not the brightest idea.