Carbon geoengineering - some examples and impacts

Table of Contents


Geoengineering in brief

Solar geoengineering - some examples and impacts

Carbon geoengineering, some examples and impacts

Community participation and inclusion in impact assessments

Unlike solar geoengineering, carbon geoengineering addresses the root cause of climate change by removing carbon dioxide (CO2), a major greenhouse gas, from the atmosphere. These techniques are also referred to as carbon dioxide removal (CDR) or more simply, carbon technologies.

Ocean fertilization is one CDR technique. The theory is to trigger large blooms of algae by ‘fertilizing’ the iron-deficient ocean with iron sulphate. The algal bloom would absorb carbon, removing it from the atmosphere and then store it by sinking to the sea floor. Thirteen field trials have been conducted since the 1990s, but they have not been successful. One reason is that iron particles sink too quickly and thus have limited opportunity to stimulate algal growth. As a result, some scientists have concluded that ocean fertilization is not an appropriate technique, while others are calling for larger-scale field trials.

The CBD draft report on Impacts of Climate Related Geo-engineering on Biological Diversity raises a number of concerns

For ocean fertilization technique to work, biological primary production (photosynthesis by algae and bacteria) will increase, inevitably involving changes in phytoplankton community structure and diversity, with implications for the wider food-web…More permanent changes are however likely if ocean fertilization is sustained, and carried out on a climatically-significant scale. Such changes may include an increased risk of harmful algal blooms, involving increased toxic diatoms.1

But as CDR slows global climate change by addressing root causes, it may also reduce negative impacts on biodiversity deriving from climate change. Ocean acidification, for example, may be diminished as CDR reduces the atmospheric carbon that is the cause. However, some scientists believe that ocean fertilization may slow near-surface acidification, while increasing acidification of the deep ocean.2

Phytoplankton (algal) blooms that would be triggered by ocean fertilization would also affect fish stocks, but not in a uniform manner. The CBD report explains that fish stocks could be expected to ‘generally increase in response to increased phytoplankton … arising from ocean fertilization’ but that they could also ‘decrease in … areas where primary production is reduced.’

Figure 1.  Changes in primary production after 100 years of global iron fertilization

Projected increases (red, orange and yellow) and decreases (blue) in vertically integrated primary productivity (gC/m2/yr) after 100 years of global iron fertilization. 

During the 2009 Climate Conference in Copenhagen, Fiu Elisara, Samoan Executive Director of the O le Siosiomaga Society and indigenous representative to the UN climate negotiations, reported on new climate technologies:

For us in the Pacific, it is important to ensure that on top of being victims of the climate crisis, we do not want to become guinea pigs for new unproven technologies or old hazardous technologies such as nuclear power with the excuse that more technology is needed to fix the climate. As one colleague said here in Copenhagen, "It is totally irresponsible that negotiators are discussing the development and the transfer of technologies without any mechanisms to filter which ones can be useful and which ones will create more problems for peoples and the environment. We need immediately the inclusion and application of the precautionary principle on the issue of technology".

But not all geoengineering technologies are new. In contrast with ocean fertilization, land-based carbon reduction technologies are more familiar to indigenous peoples and local communities, especially those living in or near forested areas. These technologies include afforestation – or the planting of trees on land that has not had forest for more than 50 years – and reforestation – planting trees in areas that have been deforested more recently. They also include biochar which is a technique that turns biomass into charcoal.

The rationale behind such techniques is the following. Tree and plant biomass absorbs carbon dioxide as it grows. When this biomass is burned or left to rot on the ground, the absorbed carbon dioxide is released back into the atmosphere. Biochar technologies break this cycle by stocking carbon in the form of charcoal which is then buried in the soil.

These technologies have won the enthusiasm of some biodiversity scientists. Thomas Lovejoy argues:

At the moment, roughly half the excess carbon dioxide in the atmosphere comes from destruction and degradation of ecosystems over the past three centuries. A significant amount of CO2 can be withdrawn by ecosystem restoration on a planetary scale. That means reforestation, restoring degraded grasslands and pasturelands and practicing agriculture in ways that restore carbon to the soil. There are additional benefits: forests benefit watersheds, better grasslands provide better grazing and agricultural soils become more fertile. This must integrate with competing uses for land as the population grows, but fortunately it comes at a time of greater urbanization.3

Indigenous peoples have long advocated the restoration of degraded forests with native trees, and biochar itself is inspired by 'terra preta' soils in Amazonia that were created hundreds of years ago by pre-Colombian settlements that incorporated charcoal into soils to increase their fertility.

Are there concerns about biochar techniques? The CBD draft report cautions:

[t]he storage or disposal of biomass may have impacts on biodiversity separate from those involved in (biochar) production. Removal of biomass from agricultural ecosystems may have negative impacts on agricultural productivity and biodiversity. 4

Biochar projects have already been implemented across Africa, and afforestation and reforestation projects are common. However, these technologies would have to be implemented on a massive scale to have the desired effect on the earth's atmosphere. Might not large-scale CDR technologies threaten existing biodiversity, indigenous peoples’ rights to land and the use of land for ensuring food security?

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1 See Section Direct external ocean fertilization techniques, with reference to Changes in phytoplankton community structure and diversity and food webs, of the CBD draft report on Impacts of Climate Related Geo-engineering on Biological Diversity, available at

2 See Section Direct external ocean fertilization techniques, with reference to Ocean Acidification, , of the CBD draft report on Impacts of Climate Related Geo-engineering on Biological Diversity, available at

3Lovejoy, Thomas, 2011. Geo-engineering can help save the planet. New York Times. Available at

4See Section Direct external ocean fertilization techniques, with reference to General Issues on Biomass Production, of the CBD draft report on Impacts of Climate Related Geo-engineering on Biological Diversity, available at