Climate: Deep oceans likely to feel CO2 legacy for centuries

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Melting sea ice around Greenland. @bberwyn photo.

‘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’

Staff Report

FRISCO — Removing CO2 from the atmosphere as a last-ditch effort to avoid dangerous climate change probably wouldn’t be enough to ameliorate impacts to the world’s oceans, where the legacy of carbon pollution will likely play out for centuries to come in the form of deep ocean heat and increasing acidification.

These changes would linger even if the atmospheric carbon dioxide concentration were to be restored to pre-industrial levels at some point in the future, according to a new Nature Climate Change paper from an international team including Ken Caldeira, of the Carnegie Institution. This is due to the tremendous inertia of the ocean system.
The report tried to assess whether proposals to actively remove CO2 could help avert some of the most serious impacts of global warming, but none of the proposed removal and storage strategies have been proven at a large scale. The computer models used by the scientists showed that time is running out — if large-scale CO2 removal technologies are used too late, they might as well not be applied at all, as far as ocean acidification is concerned, the team found.

“Geoengineering measures are currently being debated as a kind of last resort to avoid dangerous climate change–either in the case that policymakers find no agreement to cut CO2 emissions, or to delay the transformation of our energy systems,” said lead-author Sabine Mathesius from GEOMAR Helmholtz Centre for Ocean Research Kiel and the Potsdam Institute for Climate Impact Research. “However, looking at the oceans we see that this approach carries great risks.”

The study was framed in the context of what might happen if  various near- to mid-term climate policy targets are not achieved.

“If we overspend our carbon dioxide emission budget now, can we make up for it by paying back a carbon dioxide debt later?” asked Caldeira, who worked on this issue during a research stay at PIK. “Can later carbon dioxide removal from the atmosphere offset today’s emissions?”

With the computer model, the scientists studied the effects of various levels of Co2 removal, including a rate of  22 billion tons per year, which remove carbon dioxide at slightly more than half current emission rates.

“Interestingly, it turns out that after business-as-usual until 2150, even taking such enormous amounts of carbon dioxide from the atmosphere would not help life that exists deep in the ocean very much. After large-scale ocean circulation has transported acidified water to great depths, it is out of reach for many centuries, no matter how much carbon dioxide is removed from the atmosphere,” Caldeira said.

“In the deep ocean, the chemical echo of this century’s CO2 pollution will reverberate for thousands of years,” said co-author John Schellnhuber, director of PIK. “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.”

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