Urban afforestation aside, my final urban geoengineering post considers...
...Urban Mineral Weathering(MW)!
Naturally, global silicate mineral weathering captures just 0.1 GtC a year, less than 1% of current emissions. When silicate minerals Calcium(Ca) and Magnesium(Mg) react with dissolved CO2 in the soil, they form carbonates and act as an inorganic carbon sink(as opposed to the organic sinks of last post's afforestation). Industrial MW involves carbonate in batch reactors, with pre-treatment and high temperatures requiring extensive energy use and costs. Recent studies suggest urban soils may be used in passive carbonate formation to act as stable sinks. Urban soils have complex formation histories, with cement and mortar enriching urban soils with Ca and Mg to a far greater concentration than non-urban soils.
MW in action
A study in Newcastle-upon-Tyne(See figure 1) found that an urban demolition site sequestered 12.5 tonnes of Carbon a year, with capacity to store 64,800 tonnes of CO2 in carbonate. Unlike organic biosphere storage, this forms stable soil based stocks. Other studies have concluded that manipulating both inorganic and organic capture with biochar, could sequester a 1,000,000 tonne carbon annually in UK cities alone, putting MW at the forefront of research. These studies suggest a 100 tonne storage per hectare capacity. So while the UK bears 1.7 million hectares of urban land, extrapolating to the global urban land of 360 million hectares seems relevant. The full potential of this itself has been estimated to be 700-1200 million tonnes of CO2 per year, making MW a significant form of CDR for future consideration.
My only critique here is in Washbourn's suggestion that we make Ca and Mg enrichment a routine element in urban construction strategies. Without fully understanding the consequences of continued enrichment, this may be something we should consider only after further research of this technology, an ethos relevant in the majority of geoengineering practices. Although this is an area of research still in its infancy, developing this technology may yield game changing impacts.
Cement Carbonation(CC)
Another method to implement urban CDR is through cement. I know. Awesome companies like Solidia Cement and Iron Shell have developed cement that actually absorbs carbon dioxide in solidification processes. This video really sets it all out:
Solidia's rhetoric is highly win-win oriented concerning their product's implications for urban developments. Sustainable development technologies are going to have to be able to assimilate into the economic consumerist status quo to become popularized, but is this really the takeaway message we should be giving in mitigation and geoengineering strategy? This method may fit into the life cycle of mineral weathering, but conflicts with areas available for afforestation.
Consuming our way to sustainability with technologies that absorb carbon and ecologically centered afforestation both have benefits and set backs. Echoing my conclusions from last week, integrating urban CDR with urban and non-urban mitigation seems the most plausible solution to our puzzle. Diversification is important in developing closed loop urban environments that can provide both ecological and life services to residents. While cities may not be quite the Finkian cornucopias of geoengineering outlined in my urban geoengineering governance post, as leading polluters and innovators, their adoption of afforestation, mineral weathering and carbon capture techniques will doubtlessly contribute to our overall goals in achieving negative emissions by 2100, while not being a standalone solution in this ongoing and complex challenge.
...Urban Mineral Weathering(MW)!
Naturally, global silicate mineral weathering captures just 0.1 GtC a year, less than 1% of current emissions. When silicate minerals Calcium(Ca) and Magnesium(Mg) react with dissolved CO2 in the soil, they form carbonates and act as an inorganic carbon sink(as opposed to the organic sinks of last post's afforestation). Industrial MW involves carbonate in batch reactors, with pre-treatment and high temperatures requiring extensive energy use and costs. Recent studies suggest urban soils may be used in passive carbonate formation to act as stable sinks. Urban soils have complex formation histories, with cement and mortar enriching urban soils with Ca and Mg to a far greater concentration than non-urban soils.
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| Figure 1: The Newcastle-upon-Tyne Science Central Space, formerly the grounds of a brewery and the site of intense interest around carbonate formation as CDR for urban application; source: Newcastle University |
MW in action
A study in Newcastle-upon-Tyne(See figure 1) found that an urban demolition site sequestered 12.5 tonnes of Carbon a year, with capacity to store 64,800 tonnes of CO2 in carbonate. Unlike organic biosphere storage, this forms stable soil based stocks. Other studies have concluded that manipulating both inorganic and organic capture with biochar, could sequester a 1,000,000 tonne carbon annually in UK cities alone, putting MW at the forefront of research. These studies suggest a 100 tonne storage per hectare capacity. So while the UK bears 1.7 million hectares of urban land, extrapolating to the global urban land of 360 million hectares seems relevant. The full potential of this itself has been estimated to be 700-1200 million tonnes of CO2 per year, making MW a significant form of CDR for future consideration.
My only critique here is in Washbourn's suggestion that we make Ca and Mg enrichment a routine element in urban construction strategies. Without fully understanding the consequences of continued enrichment, this may be something we should consider only after further research of this technology, an ethos relevant in the majority of geoengineering practices. Although this is an area of research still in its infancy, developing this technology may yield game changing impacts.
Cement Carbonation(CC)
Another method to implement urban CDR is through cement. I know. Awesome companies like Solidia Cement and Iron Shell have developed cement that actually absorbs carbon dioxide in solidification processes. This video really sets it all out:
Solidia's rhetoric is highly win-win oriented concerning their product's implications for urban developments. Sustainable development technologies are going to have to be able to assimilate into the economic consumerist status quo to become popularized, but is this really the takeaway message we should be giving in mitigation and geoengineering strategy? This method may fit into the life cycle of mineral weathering, but conflicts with areas available for afforestation.
Consuming our way to sustainability with technologies that absorb carbon and ecologically centered afforestation both have benefits and set backs. Echoing my conclusions from last week, integrating urban CDR with urban and non-urban mitigation seems the most plausible solution to our puzzle. Diversification is important in developing closed loop urban environments that can provide both ecological and life services to residents. While cities may not be quite the Finkian cornucopias of geoengineering outlined in my urban geoengineering governance post, as leading polluters and innovators, their adoption of afforestation, mineral weathering and carbon capture techniques will doubtlessly contribute to our overall goals in achieving negative emissions by 2100, while not being a standalone solution in this ongoing and complex challenge.
Hi Coskun, great blog post! I liked the Newcastle-Upon-Tyne case study and that you made this relevant to the UK. I think it would be really interesting to consider the potential of these geo-engineering techniques in less wealthy countries/cities in order to see whether they are accessible and feasible globally.
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