Réponse:

Dear Mr Sollberger, thank you for your question posed to Ms Valery Detemmerman from the World Climate Research Programme, World Meteorological Organization.

Large-scale fertilisation of the ocean is being actively promoted by various commercial organisations as a strategy to reduce atmospheric CO2 levels. However, the current scientific evidence indicates that this will not significantly increase carbon transfer into the deep ocean or lower atmospheric CO2. Scientists from around the world note that ocean acidification due to oceans' uptake of atmospheric CO2 is already detectable, and is accelerating. Ocean acidification, along with warming surface waters and changes in ocean mixing, may reduce the ability of the ocean to absorb CO2, leaving more CO2 in the atmosphere and worsening its impact on the climate. Such a reduction would make it more difficult, and more expensive, to stabilize atmospheric CO2 concentrations. Furthermore, there may be negative impacts of iron fertilization including dissolved oxygen depletion altered trace gas emissions that affect climate and air quality, changes in biodiversity, and decreased productivity in other oceanic regions. It is critical and essential that robust and independent scientific verification is undertaken before large-scale fertilisation is considered. Given our present lack of knowledge, the judgement of various international organisations from within the 'Ocean Acidification Network' is that ocean fertilisation will be ineffective and potentially deleterious, and should not be used as a strategy for offsetting CO2 emissions.

The primary way to protect the ocean from the threat of ocean acidification is to reduce CO2 emissions. It appears impractical to chemically reverse acidification (e.g. through iron fertilization) at the scale of the world ocean through engineering approaches, and there are unknown risks for marine ecosystems associated with such large-scale manipulations of ocean chemistry. An issue of this magnitude with such high uncertainties poses an enormous challenge to the world's decision-makers, already uncomfortable making decisions when there is uncertainty about unprecedented, long-term, intergenerational problems. A global effort is required to reduce these uncertainties and to allow meaningful ecological and economic projections. This effort will require globally coordinated research, including an effective method for setting priorities, standardization of experimental procedures, information and data sharing, and long-term funding.

For more information please consult the 'Ocean Acidification Network' (http://ioc3.unesco.org/oanet/Resources.html).