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Here is a radical solution to dangerous climate change: create lakes of liquid carbon dioxide on the seabed, and keep the greenhouse gas out of the air.
As well as cutting our emissions of carbon dioxide, it is becoming increasingly likely that we will have to actively remove the gas from the air to keep Earth’s temperature at a safe level – which is now agreed to be no more than 1.5 °C above that in preindustrial times.
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But where should we put the carbon? Most attention has focused on burying it underground, perhaps by injecting it into depleted oil and gas fields. This approach has been tested and seems to work, but it is unclear whether people will accept this fix.
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Now Steve Goldthorpe, an energy analyst based in New Zealand, has suggested a radical alternative: dump the carbon dioxide in deep ocean trenches, where it can sit permanently as a liquid lake.
The crucial point, says Goldthorpe, is that once the carbon dioxide reaches a depth of about 3000 metres, its density exceeds that of water – so it will naturally sink to the bottom and stay there.
Very large carbon sink
Goldthorpe used Google Earth to explore the seabed and identify a suitable storage site. He found a deep ocean trench around 6 kilometres down, called the Sunda trench, just south of the Indonesian archipelago. “It is big enough to accommodate 19 trillion tonnes of liquid CO2, which is greater than all the CO2 from the total global fossil fuel emissions,” he says.
Carbon dioxide lakes like this do form naturally. In 2006, Fumio Inagaki of the Japan Agency for Marine-Earth Science and Technology in Yokosuka described a lake of carbon dioxide deep in the East China Sea, covered with a layer of sediment (PNAS, doi.org/czf9t4).
Ken Caldeira of the Carnegie Institution for Science in Stanford, California, has considered a similar proposal – dissolving carbon dioxide in the deep ocean – in a study published in 2008 (Elements, doi.org/brm6wp). This idea ultimately fell out of favour, largely because the carbon dioxide would react with water to form carbonic acid, making the water more acidic – with potentially harmful effects on marine ecosystems.
Caldeira says a deep-sea carbon dioxide lake would probably need a physical barrier, “perhaps some sort of plastic sheeting”, to keep the liquid trapped. “Something like giant plastic-encased sausage-like tubes of liquid CO2 lying on the sea floor could potentially store CO2 safely and securely for many millennia.”
But Caldeira says the biggest issue would be location. “Most likely, people will want to store the carbon near where the power plants are,” he says. Deep ocean trenches, by their nature, tend to be a long way away from drilling sites and power plants – so shipping the carbon dioxide to them would be expensive.
Journal reference: Energy Procedia, DOI: doi.org/10.1016
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