Atmospheric concentrations of carbon dioxide (CO2) have increased as a result of human activity – such as burning coal, oil and natural gas – from 280 ppm in pre-industrial times to 375 ppm today. CO2 emissions are the main cause of global warming and there is a worldwide effort to reduce these emissions, namely under the umbrella of the Kyoto Protocol.
Carbon dioxide capture and storage (or CCS) could play an important role in reducing CO2 emissions and is being evaluated as a way of storing CO2 over periods of hundreds, even thousands of years. Indeed, according to a new International Energy Agency (IEA) report, CCS in power generation, industry and fuel transformation could account for 20% of CO2 savings (or 6.5 Gt of CO2 captured and stored annually in 2050).
Many CCS techniques already exist today, but they are a long way from being optimized. In the most common process, carbon dioxide is extracted from a slue of waste gases. The exhaust is then sent through a chimney, from which the CO2 is extracted by chemical means and then compressed, ready for storage. Similar techniques have been used by the oil and gas industry for decades to enhance oil recovery.
The CO2 could be stored in geological reservoirs – in old oil fields, natural gas reservoirs, deep saline aquifers and unmineable coal seams, for example – and would be pumped underground via wells. Other options include storing the CO2 in deep sea sediments or fixing it in stable carbonates. Both these techniques are still in the research phase, though researchers say that underwater sequestration might be safer than storing CO2 underground on land.
There is no doubt that further advances in technology are needed, though this is not the only problem. For starters, says the IEA study, governments need to adopt climate change policies that put a cost on emitting CO2. If they do not do this, there will be no incentive to use CCS.
One problem, many solutions
What's more, CCS is only a "bridge" solution to solve the problems of CO2 emissions over the next hundred years or so, during which time fossil fuels will still be the main source of energy. We must not forget that the most important solutions to the climate change problem are energy efficiency and cleaner, renewable energy sources. Indeed, CCS has been criticized by environmental groups, like Greenpeace, as detracting from "real issues", such as pollution and producing large amounts of CO2 in the first place.
Another big drawback of CCS is that the process itself requires energy and that, conversely, adopting it may actually lead to an increase in our use of fossil fuels. For example, to produce the same amount of energy, a power plant with CO2 capture would need 10 to 40% more energy than a plant without capture. This would increase the cost of producing electricity (by as much as 5 cents/kWh of power according to the UN Intergovernmental Panel on Climate Change), which may be difficult to subsidize since industry and the public now expect cheap electricity.
Of greater immediate concern are the non-negligible hazards to human health, says the IEA study. These include possible leakage of CO2 from underground depots, which would contaminate groundwater and increase the water's acidity, leading to toxic chemicals such as lead being leached out from rocks. Other dangers associated with leakage include asphyxiation if CO2 levels rose to 7 to 8% by volume of air. There are also risks inherent in transporting CO2 (the gas must be liquefied under high pressure) and in injection processes. All of these problems need to be further studied and overcome if the technology is to be employed on a wide scale.
Finally, there are all sorts of thorny legal issues to resolve, including how the law would treat CCS activities in international seas and which organisations would be responsible. And as the IAE study notes, one thing is certain: new partnerships are going to be essential – most notably between CO2 producers, transporters, storage providers, host communities and governments, if CCS is to become a mainstream technology.