Iron the sea to combat climate change

[http://www.sciencemag.org/cgi/content/full/318/5855/1368](http://www.sciencemag.org/cgi/content/full/318/5855/1368)


With no doubt, climate change is one of the biggest challenge the mankind faces in the new century. Perhaps this explains why there are quite some strange proposal to battle increasing green house gases. For example, there are some researchers proposed to [increase aerosol in the atmosphere to block solar radiation](http://www.guardian.co.uk/environment/2007/jan/27/usnews.frontpagenews) as aerosol is observed to lead to [temperature decrease in some cities in China](http://www.terradaily.com/reports/Haze_Dynasty.html) and [may cancel out some effects of global warming](http://www.sciencemag.org/cgi/content/summary/283/5406/1273). This somehow reminds me of ``Operation Dark Storm'' in [Animatrix](http://en.wikipedia.org/wiki/The_Second_Renaissance#Part_II). But of course such a proposal will get almost nil support from any reasonable person.

Now here is the new idea: pump iron into the sea. As the sea has a sufficient level of nutrient already and iron is the limiting factor, this will lead to virtually an explosion of algae which will need considerable amount of carbon to grow and will rapidly sink into the sea, which may be a way of sequestrating carbon. If practical, this will be a cheap solution to reduce carbon in the atmosphere. However, from the article in science you can read a lot of suspicions with various reasons: altered ecosystem, the efficiency of the sinking process, and the methane and nitrous oxide emitted in the process.

As there are too many uncertainties, further experiments are desirable. This is supported by some companies which hope to earn some credits in the carbon trading system. Personally I hope the experiment a success. However I also have my own doubt: will the sea saturate? There are reports saying that the capability of ocean carbon sinks are decreasing, and in a recent article, Canadell et al. states:

[C]arbon emissions have grown faster than CO2 sinks on
the land and oceans. Because the land and oceans are
both mosaics of regions that are gaining and regions that
are losing carbon, this trend could result from any or all
of three scenarios: sink regions could have weakened,
either absolutely or relative to growing emissions; source
regions could have intensified; or sink regions could have
transitioned to sources. (Canadell et al. 2007)

And Le Quere et al. (2007) have reported that the Southern Ocean is losing ability to absorb carbon dioxide and becoming a source instead.

I know very little about the metabolism of algae and the biochemical process in the ocean, but I think the researchers proposing the experiment should also consider carbon that cannot make it to a depth below 500 metres. Will they enter the ocean and accelerate the saturation of carbon? If so, in what condition?

My other complain is that this proposal, even if a success, should not be relied upon as a solution to climate problem. It should function more as a means to slow the process of climate change and earn some time for mankind to ultimately solve the carbon balance. I am worried that successful carbon sequestration will only lead to more emission. A mature carbon trading system may help, but a global monitoring and enforcement system urging everyone's adaptation to cleaner energy and smaller carbon footprint is the solution.

1. J. G. Canadell et al., [“Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks,”](http://www.pnas.org/cgi/reprint/0702737104v1.pdf) Proceedings of the National Academy of Sciences (2007).

2. C. Le Quere et al., “Saturation of the Southern Ocean CO2 Sink Due to Recent Climate Change,” Science 316, no. 5832 (June 22, 2007), [http://www.sciencemag.org/cgi/content/abstract/316/5832/1735](http://www.sciencemag.org/cgi/content/abstract/316/5832/1735).