The IPCC calculates that it will only be possible to limit global warming to less than 2 degrees Celsius by removing carbon dioxide from the atmosphere. But just how safe is deep-sea or underground carbon storage? Elke Bunge reports.
2016 became the first year in which global carbon dioxide concentrations atmosphere exceeded the critical mark of 400 parts per million (ppm).
Over the past few years, climate researchers have warned repeatedly that exceeding this mark would make it impossible to limit global warming to less than 2 degrees Celsius above pre-industrial levels. In other words: climate change is likely unavoidable.
Intent on averting this, the participating nations at the UN climate conference in Paris last December issued voluntary commitments to reduce their carbon dioxide emissions. The details of these are now being hammered out in Marrakech, Morocco.
But instead of focusing solely on dramatically reducing greenhouse gas emissions, many governments are contemplating carbon-reduction plans that will suck tonnes of carbon dioxide directly from the atmosphere and store it — a technology known as carbon capture and storage (CCS).
Technology still experimental
Scientists around the world are occupied with the problem of negative emissions. Using the latest technological means available, they are working to filter carbon dioxide out of the air and store it in saline solutions deep underground or in the seabed.
The carbon storage facilities themselves have to be located at a depth of at least 800 metres; only there is the pressure strong enough to compress the carbon dioxide.
But unlike propane or butane, CO2 cannot be liquefied. In thermodynamic terms, this means that the gas remains in a supercritical state.
In order to prevent any leakage, the storage containers would have to be sealed with a gas-impermeable material — a cost-intensive, technologically complex process. For now at least, no one has yet to find a satisfactory solution to this.
Researchers expect that these as-yet experimental technologies will be ready to store carbon dioxide safely in the next 15 to 20 years.
Germany, for instance, has an estimated storage capacity of 20 billion tonnes of CO2, making it possible to store emissions from all German power stations for up to 50 years.
Shifting the problem to future generations
But critics of the technology see it otherwise; for them, it’s merely shifting the problem to future generations.
In a recently published study, authors Kevin Anderson from the University of Manchester and Glen Peters from the Center for International Climate and Environmental Research in Oslo (CICERO) warn against the unforeseeable dangers of CCS technology.
Apart from the fact that carbon dioxide could re-enter the atmosphere after a certain period of time as a result of cold-water geysers or other causes, outgassing could also carry toxic heavy metals from the rocks into the groundwater.
And in Norway, the practice of inserting CO2 for the production of oil and natural gas has already triggered seaquakes.
“Negative emission technologies are not an insurance policy,” said Professor Anderson.
“They are a high-risk gamble with tomorrow’s generations, particularly those living in poor and climatically vulnerable communities, set to pay the price if our high stakes bet fails to deliver as promised.”