The planet is warming. The release of CO2 and other greenhouse gases, from the burning of fossil fuels and other human activities, is causing global temperatures and sea levels to rise, glaciers to melt, and climate patterns to change all over the world. It’s also affecting the oceans.
Since the Industrial Revolution, 30% of the CO2 that has been emitted through the combustion of fossil fuels has been taken up by the oceans. But it comes with a cost: ocean acidification, the “other” carbon problem. I’ve written about this before here. But now there may be some good news, a new way to reduce CO2 in the atmosphere AND acid in the oceans. Read on!
The chemistry of seawater is what allows the oceans to take up so much CO2. For you chemistry buffs, here’s how it works:
* CO2 (from the atmosphere) + H2O (seawater) ⇌ H2CO3 (carbonic acid)
* H2CO3 (carbonic acid) ⇌ H+ (acid) + HCO3− (bicarbonate ion) ⇌ 2H+ (more acid) + CO3−− (carbonate ion)
The more CO2 we introduce on the left, the more the equations are driven to the right: the more acidic (H+) the oceans get. Over long time scales – and I mean really long, like millions of years – the problem is solved through carbonate weathering of rocks. Instead of the above, where H2CO3 ends up creating more acid (H+), you get this:
* CO2 (from the atmosphere) + H2O (rainwater) ⇌ H2CO3 (carbonic acid)
* H2CO3 + H2O + silicate minerals -> HCO3− (bicarbonate ion) + cations (Ca++, Fe++, Na+, etc.) + clays (which ultimately end up in the sea).
Notice that while you still have HCO3−, there’s no free H+ running around to make the water acid. Instead that HCO3− is used by creatures like corals and foraminifera to make calcium carbonate (CaCO3) shells, and ultimately buried deep beneath the seafloor when those critters die.
Or does it? Greg Rau of the University of California Santa Cruz conducted a series of experiments in his lab to see if he could make this process happen faster. He made a scrubber that mimicked the natural weathering process, using limestone and seawater. His process removed up to 97% of the CO2 from a simulated exhaust stream (the kind released from power plants). He had the gas flow over crushed limestone (weathering), then dissolved the resulting ions in seawater to make it more alkaline (less acidic).
When it’s scaled up, this process could be used to keep carbon dioxide from power plants out of the atmosphere by putting it into the sea as bicarbonate (HCO3−). Since many of these plants are located on coasts, and use massive amounts of seawater for cooling anyway, the scrubbers could be installed at existing facilities. A win for the atmosphere a win for the oceans – some good news for a change!
Rau, G. (2010). CO2 Mitigation via Capture and Chemical Conversion in Seawater, Environ. Sci. Technol., Article ASAP. DOI: 10.1021/es102671x. Publication Date (Web): December 28, 2010