From Malcolm Black, Middle LaHave, Nova Scotia, Canada
You report the idea that the use of crushed rock on agricultural land to capture carbon may also alter Earth’s reflectivity. However, this geoengineering proposal isn’t practical. A millimetre-thick layer of rock per hectare weighs around 20 tonnes. Extended to 1.5 billion hectares of cropped land in the world, and that is a lot of rock dust. I shudder at the carbon emissions from crushing it, trucking it to distant fields and spreading it (1 February, p 14).
Other potential negatives include wind erosion of the dust, which would cause pulmonary problems for humans and animals that breathe in the particles, and potentially fatal effects on insects when they are coated by the dust.
