Temperature outcomes of enhanced rock weathering deployment scenarios constrained by soil albedo measurements

Enhanced rock weathering (ERW) is a carbon dioxide removal (CDR) strategy involving spreading silicate rock powder on croplands to speed up the natural weathering process, whereby CO₂ reacts with rainwater and silicate minerals to form bicarbonate ions, which are eventually transported to and stored in the ocean. While ERW can potentially sequester gigatons of CO₂ per year and therefore help achieve the Paris Agreement goal of limiting global warming to well below 2 °C, the biogeophysical effects of cropland soil amendment are possibly significant yet poorly constrained. For example, decreased soil albedo from spreading dark rock powder (e.g. basalt) on croplands might counteract cooling from CO₂ drawdown. On the other hand, light rocks such as wollastonite skarn might enhance cooling by increasing soil albedo. Here we investigate temperature outcomes of various ERW deployment scenarios with an Earth system climate model of intermediate complexity (the UVic ESCM) constrained by albedo values measured from soil amended with varying amounts and types of rock powder. We find that, with aggressive application rates of 25 or 50 tonnes of rock dust per hectare on global cropland, ERW-induced cooling is slightly counteracted by ~5% with basalt and enhanced by ~20% with wollastonite. At basalt application rates of 10 tonnes ha^-1 or below, changes to soil albedo and thus temperature outcomes are negligible. Our results demonstrate that non-CO₂ effects of CDR deployment strategies should be considered in order to meet temperature goals while also informing best practices for ERW deployment with respect to minimizing cooling offset or maximizing cooling enhancement due to soil albedo modification.