January 22, 2013
Scientists Analyze Costs And Benefits Of Rock Dissolving Practices
Brett Smith for redOrbit.com - Your Universe Online
Geoengineering is a controversial and illegal practice that attempts to mitigate the forces of climate change on a grand scale. Many see this attempt to alter global climate via artificial means as a ℠quick fix´ with potential long-term negative effects.However, despite the contentious nature of geoengineering, scientists from the Alfred Wegener Institute in Bremerhaven, Germany decided to analyze a ℠rock dissolving´ method of geoengineering to see the potential costs and benefits.
The method analyzed in the study involves the distribution of 3.3 gigatons of the powdered mineral olivine across an area of the ocean. In theory, the mineral would change the chemistry of the ocean´s surface, causing it to uptake a large amount of carbon dioxide from the atmosphere. The heavier carbon dioxide would then be sequestered by sinking to the ocean floor.
According to their report in Environmental Research Letters, the scientists began their study by examining the initial part of the olivine-based method: the grinding process. For the sequestration method to work, the mineral would have to be ground down to particles the size of one micrometer, the scientists said.
The study´s lead author, Peter KÃ¶hler, noted that the grinding process itself uses a large amount of energy, contributing to the forces driving climate change.
"Our literature-based estimates on the energy costs of grinding olivine to such a small size suggest that with present day technology, around 30 per cent of the CO2 taken out of the atmosphere and absorbed by the oceans would be re-emitted by the grinding process,” he said.
Using computer models, the scientists analyzed six different olivine distribution scenarios. Their analyses showed that 92 percent of the carbon dioxide taken up by the oceans in each scenario would be caused by chemical changes in the water.
The remaining 8 percent of carbon sequestration would be due to the fertilizing effects of olivine on marine life. Previous research has shown that the nutrients contained within olivine would also encourage phytoplankton growth. The greater numbers of phytoplankton would utilize carbon dioxide to grow, resulting to carbon sequestration by sinking to the ocean floor after dying and taking the greenhouse gas with it.
"In our study we only examined the effects of silicate in olivine,” KÃ¶hler said. “Silicate is a limiting nutrient for diatoms — a specific class of phytoplankton. We simulated with our model that the added input of silicate would shift the species composition within phytoplankton towards diatoms.”
"It is likely that iron and other trace metals will also impact marine life if olivine is used on a large scale. Therefore, this approach can also be considered as an ocean fertilization experiment and these impacts should be taken into consideration when assessing the pros and cons of olivine dissolution," he added.
The researchers also investigated if this geoengineering method could counteract ocean acidification, which negatively impacts marine life. They found that annually dissolving about 44 gigatons of olivine would fully counteract modern carbon dioxide emissions.
"If this method of geoengineering was deployed, we would need an industry the size of the present day coal industry to obtain the necessary amounts of olivine,” KÃ¶hler said. “To distribute this, we estimate that 100 dedicated large ships with a commitment to distribute one gigatonne of olivine per year would be needed.”
"Taking all our conclusions together — mainly the energy costs of the processing line and the projected potential impact on marine biology — we assess this approach as rather inefficient. It certainly is not a simple solution against the global warming problem,” he concluded.