Climate change lifesaver

Adding lime to the oceans may help reverse the rise in atmospheric carbon dioxide, according to a report in the journal Chemistry & Industry. Petrochemicals giant Shell is pumping money into a feasibility study of the idea, which might one day reduce, if not reverse, the impact on climate change of fossil fuel use, the scheme’s proponents hope.

The theory, being developed as an open source concept under the name Cquestrate, suggests that adding lime (primarily calcium oxide) to seawater will increase its alkalinity and so boost the seawater’s ability to absorb carbon dioxide from the air. Moreover, it will reduce the water’s tendency to release the gas back into the air. However, until recently the idea was thought to be unworkable because of the expense of obtaining lime from limestone and the amount of carbon dioxide that would be released in the process. Additionally, there are issues associated with the macroscale chemical engineering that will be required to have a global effect.

Could pouring lime into the oceans be a climate change lifesaver? (Photo by David Bradley)

We think it’s a promising idea, says Shell’s Gilles Bertherin, a coordinator on the project, There are potentially huge environmental benefits from addressing climate change – and adding calcium hydroxide to seawater will also mitigate the effects of ocean acidification, so it should have a positive impact on the marine environment.

Tim Kruger, a management consultant at London firm Corven, who previously worked for Shell, is the brains behind the plan to implement the lime process. He argues that it could be made workable by locating it in regions that have a combination of low-cost ‘stranded’ energy considered too remote to be economically viable to exploit – like flared natural gas or Solar energy in deserts – and that are rich in limestone, making it feasible for calcination to take place on site as it requires the strong heating of limestone.

Australia’s Nullarbor Plain visible as the smooth croissant shaped coastal region in this NASA satellite image (Credit Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC)

Kruger says: There are many such places – for example, Australia’s Nullarbor Plain would be a prime location for this process, as it has 10000 cubic kilometres of limestone and soaks up roughly 20 megajoules per square metre of Solar irradiation every day. Kruger told Spotlight that to sequester several billion tonnes of carbon dioxide requires 1.5 cubic kilometres of limestone. Of course, the scheme ignores the environmental impact on pristine wilderness, such as the Nullarbor Plain.

Of course, the process of making lime generates carbon dioxide, but adding the lime to seawater absorbs almost twice as much carbon dioxide. The overall process is therefore carbon negative. This process has the potential to reverse the accumulation of carbon dioxide in the atmosphere, Kruger says. He believes it should be possible to reduce atmospheric carbon dioxide to pre-industrial levels. The oceans are already the world’s largest carbon sink, absorbing 2 billion tonnes of carbon every year. Increasing absorption ability by just a few percent could dramatically increase carbon dioxide uptake from the atmosphere. Klaus Lackner of Columbia University tentatively agrees, The theoretical carbon dioxide balance is roughly right…it is certainly worth thinking through carefully.

The fact that the concept is open source means that anyone with the will and the means could develop the required technology. However, it is likely to require vast tonnages of raw material, which must be mined and sourced and then spread into the oceans. So the question of it being carbon negative must be considered in detail taking into account the whole process lifecycle.

There are also issues of oceanic pH change in such a way as to interfere with the very ecosystems, including fragile coral reefs, that are already under threat from climate change. Researchers must investigate possible unforeseen outcomes with such a massive chemical experiment, especially, given the inconclusive and often negative results with other macro chemical engineering schemes, such as nitrogen control and iron seeding of the oceans.

With the hint of lime concept, a lot more theoretical work must be done before we plunge into a campaign to attempt to modify the oceans in this way. We’re looking at computer simulations of the process and will progress to small-scale laboratory tests first, Kruger told Spotlight, there’s certainly no intention to just dump lime into the oceans.

Climate change lifesaver

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