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| 08/13/15

Sucking carbon out of the air won’t reverse ocean acidification


Fresh research out this week suggests that sucking carbon out of the air may assist with arresting global warming, but won’t reverse ocean acidification for centuries or even millennia.

Direct capture of carbon from the atmosphere has long been suggested as a possible high-tech way to prevent catastrophic climate change. A range of technologies that fall under the umbrella of this method, known as carbon dioxide (CO2) removal, or CDR, do exist, but are years or perhaps decades away from being commercialized.

But it is sometimes forgotten that increased carbon concentrations in the atmosphere also have a profound impact on the world’s oceans. Some 30-40 percent of the CO2 that we emit is absorbed by the sea, where it reacts with water to form H2CO3, or carbonic acid. This ocean acidification process depresses the metabolic rates and immune responses of organisms and makes it harder for plankton and corals to form their carbonate-based structures, which in turn threaten species higher up the food chain that depend on them.

Two possible future courses of events were modeled in the new research and both imagine that significant CDR efforts are mounted but otherwise no emissions cuts are made—a scenario referred to amongst climate scientists and policy makers as ‘business as usual’.  The first would see 5 gigatons of carbon sucked out of the atmosphere annually—equivalent to half the 9.9 gigatons humans pumped out in 2013, and the second, an even more gargantuan effort, envisages a “probably infeasible” 25 gigatons being vacuumed up.

For both outlooks, the situation for the ocean remains grim. Neither is able to ‘turn the clock back’ and restore ocean pH to pre-industrial levels. And neither is even able to ‘rewind’ the state of acidity to that which would occur if humanity kept to the most stringent low-carbon scenario considered by the Intergovernmental Panel on Climate Change (IPCC).

The reason is that while the surface layers of the ocean are immediately affected, acidic waters are slowly taken into the deep ocean, producing a long-term ‘memory’ of anthropogenic effects on the sea. The pH of the deep ocean would only be restored after a very slow overturning and return contact with the remediated, low-carbon atmosphere, a process that would take millennia. Thus regardless of the amount of CDR, worsening ocean acidification is with us for a long time to come in the absence of serious emissions cuts.

Another paper, also recently published in Nature Climate Change, showed how anthropogenically driven acidification isn’t just a problem for oceans, but also freshwater systems as well here in British Columbia, with profound consequences for some of the fish we eat. The researchers found that pink salmon that start out their lives in very acidic rivers are smaller and less likely to survive.

“Most of the work on acidification has been in the ocean, yet 40 per cent of all fish are freshwater. We need to think about how carbon dioxide is affecting freshwater species,” said UBC zoologist Colin Brauner.

In depth

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