Geoengineering can be divided into two broad approaches. The first is to deflect sunlight back into space through such techniques as, mimicking volcanoes by dispersing sulfate aerosols in the stratosphere, making ocean clouds more reflective, painting roofs white, etc. The second broad approach is to remove CO2 from the atmosphere.
In this second category, fertilizing the oceans with iron to enhance algae growth is an approach that has received a lot of attention for many years. Algae presently absorbs large quantities of CO2, converting it to additional plant material which then becomes part of the ocean food chain. The portion of ocean life which dies and sinks to the ocean depths becomes permanently sequestered carbon. Iron is a limiting nutrient in most sea water, so adding more iron does increase algae growth, which in turn consumes more CO2. The main questions are: How much of this CO2 will become permanently sequestered? and, What are the side effects on other ocean processes?
Because of the high level of interest in ocean fertilization, UNESCO scientists prepared a 20 page report on the subject (released in late Jan, 2011). The report not only raises serious concerns about the side effects, such as “risk of toxic algal blooms, ....sub-surface oxygen levels, biogas production and ocean acidification”, but it also predicts that the effectiveness of CO2 removal will be no where near as great as previously estimated:
“even using the highest estimates for both carbon export ratios and atmospheric uptake efficiencies, the overall potential for ocean fertilization to remove CO2 from the atmosphere is relatively small. Thus recent calculations of cumulative sequestration for massive fertilization effort over 100 years are in the range 25-75 Gt (gigatonnes) of carbon, in comparison to cumulative emissions of around 1,500 Gt carbon from fossil fuel burning for the same period under business-as-usual scenarios.”
So the risk to benefit ratio, at least for now, seems to place ocean fertilization down in the list of possible geoengineering approaches.
In this second category, fertilizing the oceans with iron to enhance algae growth is an approach that has received a lot of attention for many years. Algae presently absorbs large quantities of CO2, converting it to additional plant material which then becomes part of the ocean food chain. The portion of ocean life which dies and sinks to the ocean depths becomes permanently sequestered carbon. Iron is a limiting nutrient in most sea water, so adding more iron does increase algae growth, which in turn consumes more CO2. The main questions are: How much of this CO2 will become permanently sequestered? and, What are the side effects on other ocean processes?
Because of the high level of interest in ocean fertilization, UNESCO scientists prepared a 20 page report on the subject (released in late Jan, 2011). The report not only raises serious concerns about the side effects, such as “risk of toxic algal blooms, ....sub-surface oxygen levels, biogas production and ocean acidification”, but it also predicts that the effectiveness of CO2 removal will be no where near as great as previously estimated:
“even using the highest estimates for both carbon export ratios and atmospheric uptake efficiencies, the overall potential for ocean fertilization to remove CO2 from the atmosphere is relatively small. Thus recent calculations of cumulative sequestration for massive fertilization effort over 100 years are in the range 25-75 Gt (gigatonnes) of carbon, in comparison to cumulative emissions of around 1,500 Gt carbon from fossil fuel burning for the same period under business-as-usual scenarios.”
So the risk to benefit ratio, at least for now, seems to place ocean fertilization down in the list of possible geoengineering approaches.
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