Geo-engineering, defined here as “artificial modification of earth systems to counteract anthropogenic effects”, is gaining momentum. A commonly proposed method of doing this is to dump stuff into the ocean in the hopes that it will spur the growth of phytoplankton, which in turn will result in an uptake in CO2 from the atmosphere to the ocean. Once the plankton die they sink to the ocean floor, sequestering the CO2. As has been noted on planet doom? previously, this is a well intentioned but (likely) short-sighted attempt at a 'quick-fix' to the problems confronting humanity; a shortcut so that we can avoid making any hard choices about the world we have created.
So what is wrong with it? It is, after all, part of the natural order of things; phytoplankton blooms occur regularly now. A recent event was just observed off the coast of Namibia, in southern Africa, as shown in the MODIS imagery to the right. Phytoplankton undeniably act to sequester CO2. But, as the article notes, they have other effects as well.
After the plankton sink, they are decomposed by bacteria. If the amount of plant material is too large, the water becomes anoxic -- depleted of oxygen –- and a 'dead zone', where fish and other marine fauna are unable to survive, is created in the ocean . Needless to say, this is bad for the marine ecosystem. If material remains to be decomposed, anaerobic bacteria -- which don't need oxygen -- take over. These bacteria initiate a reaction which produces hydrogen sulfide (H2S) --a poison -- which seeps to the surface and kills the fish and other fauna.
In the local region and at the times where this occurs, it becomes a serious issue, but remains generally unimportant on larger scales. But creating more phytoplankton through geo-engineering could become a broader issue. Dead zones are already becoming a problem worldwide, particularly near the mouths of large river systems, due to agricultural runoff. Other regions with restricted water flow, like the Black Sea, are natural anoxic zones. The fact that we have these major environmental problems already being seen suggests that the amount of phytoplankton which would need to be produced to offset the 35% increase in CO2 we have put into the atmosphere to date would be very large. We probably couldn't do it without destroying a large part of the marine ecosystem.
In a paper from last year (Oct 2006) in Scientific American entitled “Impact from the Deep”, an intriguing hypothesis was put forth that a similar mechanism involving anoxic oceans and the production of H2S, rather than the more commonly assumed bolide impacts, may have driven several of the five mass extinctions which have been noted in the fossil record. In this hypothesis, anoxic zones producing H2S rise to the ocean surface and releases the gas to the atmosphere, killing nearby land flora and fauna. Further, the gas may rise to the stratosphere, where there is some indication that it may reduce the protective ozone layer, finishing off the organisms which avoid the initial impact of the gas. In that paper, the chain of events starts with rapid global warming. With geo-engineering we could possibly skip a few steps, and proceed right to the extinction.
This is only a supposition. The fact is that we simply don't know what effect such geo-engineering schemes may have. We don't have a good history at avoiding the so-called Law of Unintended Consequences and so we probably shouldn't tempt fate. Although we can and have altered the environment, it is pure hubris to think that we have any sort of control over it. As a result, we should really put aside these grandiose schemes to save the world and instead focus on the more mundane chores of adapting to the unavoidable changes already in the system and reducing our carbon emissions to mitigate any future effects. Societal collapse and the sixth extinction are distinct futures we face with our current way of life. We need to act with wisdom and forethought to avoid these fates.