Proposals to remove the greenhouse gas CO2 from the atmosphere might slow the rate of global warming but would do little to reverse climate damage to the world's oceans, researchers say.
Warming and acidification of the oceans due to human-caused emission of the heat-trapping gas would likely linger even if proposed future carbon dioxide removal schemes managed to reduce atmospheric CO2 to preindustrial levels, they warn.
Even if such reductions were possible and attained, "the acidity in the oceans could still be more than four times higher than the preindustrial level," says Sabine Mathesius at Germany's Potsdam Institute for Climate Impact Research.
The problem, researchers say, is the tremendous inertia of ocean systems.
The researchers used computer models to examine what would happen with various rates of CO2 removal from Earth's atmosphere.
One model was based on a removal of 22 billion tons annually, which would capture and store carbon dioxide at about half the current emission rate.
Any such removal technology would be decades away — none of the proposed carbon removal-and-storage strategies have been proven at an industrial scale yet — meaning levels of CO2 are likely to continue to rise with human activity until at least mid-century, they note.
"Interestingly, it turns out that after business-as-usual until 2150, even taking such enormous amounts of CO2 from the atmosphere wouldn't help the deep in the ocean that much," says research team member Ken Calderia of the Carnegie Institution in Washington, D.C. "After the acidified water has been transported by large-scale ocean circulation to great depths, it is out of reach for many centuries, no matter how much CO2 is removed from the atmosphere."
The oceans take up around a quarter of all CO2 produced by humans, where it forms carbonic acid, impacting reef growth and representing a threat to marine life by affecting biodiversity and the marine food chain.
In addition, warming of the oceans from CO2-caused climate change decreases concentrations of oxygen and reduces oceans' circulation, interfering with nutrient transport.
Similar changes to the Earth's atmosphere and oceans in the distant geological past have resulted in mass extinctions, something that could happen again, the researchers warn.
"In the deep ocean, the chemical echo of this century's CO2 pollution will reverberate for thousands of years," says John Schellnhuber, the director of the Potsdam institute. "If we do not implement emissions reductions measures in line with the 2 degrees Celsius target in time, we will not be able to preserve ocean life as we know it."
The Paris Climate Conference, which will be held in Le Bourget, Paris, from Nov. 30 to Dec. 11 later this year, brings together nations around the world to discuss ways of meeting that 2-degree Celsius goal, which is part of the goal of keeping global temperature from exceeding preindustrial levels by more than 2 degrees Celsius (3.6 degrees Fahrenheit).
The ultimate objective of the United Nations Framework Convention on Climate Change is to stabilize levels of greenhouse gases. Aside from setting a target level, a time-frame must also be set in such a way that it would give ecosystems sufficient time to naturally adapt to climate change and for economies to move forward and progress through sustainable means.