THE SUM OF human tinkering with the climate since the beginning of the industrial era is sometimes likened to a planetary science experiment. That captures the magnitude of what is happening and the unpredictability of its results, yet it is also misleading. Global warming is not an experiment, because it is not intentional. Greenhouse-gas emissions are the unfortunate side effects of useful things like modern agriculture, electricity generation and convenient transport. Mankind has not really started experimenting with the climate yet.

But perhaps, given the slow progress in keeping down emissions, it should. A small, under-financed and somewhat obsessive group of scientists is working on ways of “geo-engineering” the Earth to reverse global warming. Some of their proposals are absurdly costly; others are exceedingly dangerous. Still, geo-engineering deserves much more serious consideration than it has so far received.

Since climate change is mostly caused by greenhouse gases, the obvious way of reversing it is to remove those gases from the atmosphere. Removing carbon dioxide from the air would also help marine creatures: the oceans are becoming less alkaline as a result of dissolved carbon, which seems to be harming corals. Some scientists are exploring ways of speeding up the natural processes that already do this. Carbon-absorbing minerals like olivine, which is in abundant supply, could be mined, crushed and spread out. Lime or limestone could be tipped into the ocean to react with dissolved carbon dioxide to create bicarbonate ions, allowing the water to absorb more carbon dioxide from the air. Iron and other nutrients could be added to the water to stimulate the growth of algae, which feed on carbon dioxide.

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