Enhanced weathering creates dead zones and expands billions of coal mining emissions.

However, speeding up or changing the course of nature can have disastrous effects. Scientists suggest that rapid uncontrolled changes in pH, carbonate saturation state, and dissolved aqueous CO2 can affect ocean ecosystems. While this process mimics a natural one, it is not natural; the substance would be delivered to ecosystems at rates far higher than normal which could create ‘dead zones’, areas where oxygen levels are too low to support life. Additionally, the amount of olivine necessary for these applications is extremely large and is comparable to present-day global coal mining, a counterintuitive proposition as the planet looks to turn away from mining. In the case of basalt, to sequester one billion tonnes of CO2, more than 3 billion tonnes of basalt would have to be spread, an amount equal to almost half of the current global coal production.

Additionally, at such a large scale, enhanced weathering could change the ecology of the water, leading to an increase in the microbial organisms that produce greenhouse gases such as methane and nitrous oxide.

Although the addition of alkalinity is common practice in certain constrained marine environments such as in aquaria and shellfish production, scientists believe that more research is needed to understand the wider ecosystem response.