A recent piece in the Proceedings of the National Academy of Sciences discusses geoengineering as a way to manipulate Earth’s climate in order to counteract global warming from greenhouse gas emissions.

Using a method described as “enhanced weathering,” researchers claim that piles of chalk could be used to stabilize the climate. The chalk piles could, in theory, remove as much CO2 from the atmosphere as desired — although the practical challenges are enormous, said Tim Kruger of Oxford Geoengineering, a networking organization in the UK, speaking at a conference at the Royal Society in London earlier this week.

According to Kruger, adding calcium oxide (also known as quicklime and made from chalk) to the oceans would result in calcium hydroxide, which is strongly alkaline. This absorbs CO2 dissolved in seawater, causing the ocean to suck replacement CO2 out of the air.

“[This method has] the potential to draw down carbon dioxide without limit,” Kruger says, because the raw materials necessary are readily available.

Differences in global temperature, atmospheric CO2, and mean surface ocean pH induced by enhanced silicate weathering for A.D. 2010–2100.

Dieter Wolf-Gladrow of the Alfred Wegener Institute for Polar and Marine Research in Germany warns of some major challenges. To produce calcium oxide you have to burn chalk or limestone, producing CO2 that must be stored.

Wolf-Gladrow has looked at an alternative: scattering the common mineral olivine as a powder in humid tropical lands. Olivine reacts with CO2, but it could only remove at most 3.7 gigatons of CO2 per year – around one-tenth of our annual emissions. Too much olivine would eventually leach into tropical rivers and make them more alkaline, harming wildlife.

My initial reaction was of the potential for damaging the marine ecosystem. In the paper, Kruger states:

It would thus bring various marine calcifying species, which depend in the buildup of their hard shells
or skeletons on the oversaturation of CaCO3 in surface waters, into unfavorable environmental conditions, to which their degree of adaption is yet unknown. In the worst case their carbonate
parts might dissolve.

I would say that’s a pretty worst case” alright. But geoengineers say that these potential worst case scenarios should not prevent the public from even considering the options available. “A fear of unintended consequences which could arise from large-scale interventions in natural cycles may be seen to undermine the international commitment to reduce greenhouse gas emissions. This distrust should not prevent the objective consideration of the potential for geoengineering approaches so that they can be assessed based on factual evidence,” says Oxford Geoengineering.

The full article is available for free download here (PDF).