At the Port of Los Angeles, a long gray ship is doing its part to fight against climate change. On the ship, which belongs to Captura, a Los Angeles-based company, is a system of pipes, pumps, and containers that pumps seawater and removes CO2, which can be used to make plastics and fuels or buried. Then the treated seawater is returned to the ocean, where it absorbs more CO2 from the atmosphere, in an effort to battle the rise of the greenhouse gas.
Capturing(捕获) CO2 from the ocean should be easier and cheaper than a seemingly more direct approach: capturing it directly from the air. Direct air capture, which relies on fans to sweep air past chemicals that can absorb CO2, currently costs between $600 to $1000 per ton of CO2 removed, largely because atmospheric CO2 only makes up less than
0.05% of the air by volume. Earth's oceans, in contrast, hold the gas at a concentration nearly 150 times higher, and absorb roughly 30% of all emitted (排放) CO2 each year.
Besides, ocean capture is developing faster than other ocean CO2 removal approaches. That's partly because the systems can usually be attached to desalination (脱盐) plants, wastewater treatment equipment, and other large water-processing systems.
However, one challenge for the approach is determining exactly how much CO2 the treated water absorbs and at what rate. Still, the absorption rates will vary based on where the water is released and how easily it mixes with surrounding water. That makes site selection a really important part of this process.
Even if the technology takes off, it will have to be promoted widely to make a difference in offsetting global emissions. According to the Intergovernmental Panel on Climate Change, by 2050 engineered carbon removal efforts will need to remove some 5 billion tons of CO2 every year to limit the global temperature increase to 1.5℃. At present, the ocean capture companies are removing only thousands of tons.
