As a new climate treaty is negotiated, there's debate around decarbonization versus "net zero." But the latter relies on technologies that aren't widely implemented - or don't even exist yet.
The energy industry touts it as the solution for clean fossil fuels, and the IPCC says it will be key to preventing dangerous climate change. But while America pushes ahead with developing carbon capture and storage (CCS), Europe has increasingly cold feet.
By capturing carbon dioxide and storing it deep underground, the technology has the potential to reduce greenhouse gas emissions from power production, industry and fossil fuel refining.
But some environmentalists - and much of the European public - fear CCS is a dangerous distraction from the higher aim of giving up fossil fuels in favor of renewables.
UK backs out of CCS plans
"I think in many cases, public opinion is against CCS because of short-term concerns over health, and the safety risk of storing carbon under the ground," said Jim Watson of the United Kingdom-based Energy Research Centre. "But there are also concerns because CCS is seen as perpetuating the use of fossil fuels."
In Europe, CCS projects have been canceled due to fierce public resistance, while the UK government announced at the end of November 2015 that it was pulling 1 billion pounds ($1.5 billion) in funding originally earmarked for the development of a large-scale CCS project.
"The government's decision is a huge blow to CCS development in the UK but also to the technology in Europe as whole - and to some extent globally - because it was one of only a handful of countries investing in major CCS projects," Watson told DW.
North America takes the lead
The news came just a few weeks after Shell announced its latest CCS project in Canada to reduce emissions from processing oil from bitumen extracted from Alberta's controversial oil sands.
CCS is being used to reduce emissions from the oil processed from the controversial Alberta tar stands
Canada is also home to the Boundary Dam project, the world's first commercial CCS-fitted coal power plant, which has now been in operation for a year.
More than half the world's operational and planned CCS plants are in the US. President Obama's Clean Air Act actively promotes its use to meet emissions reduction targets, and the government has invested heavily in funding for CCS demonstration projects.
Across the pond, the European Union is enthusiastic about the technology - individual countries have been reluctant to invest. "There has been much less progress in Europe than in America," Juho Lipponen, head of the IEA's CCS Unit, told DW.
Lipponen said this was partly because in North America, CCS development was linked to terrestrial hydrocarbon production. But in Europe, fracking is still strongly opposed, and oil and gas mainly comes from offshore sources.
The CCS expert also points to public resistance and a lack of political will to implement CCS in Europe.
Low acceptance in Germany
"European governments have not been supportive enough of CCS," Lipponen said. He added that in Germany, the focus on switching to renewables had seen carbon capture sidelined.
Environmentalists say CCS is incompatible with the shift to carbon-neutral renewables - a process also known as decarbonization
Vattenfall shut down its 1.5-billion-euro German CCS project at the Schwarze Pumpe brown coal-fried power station in Germany last year because of political uncertainty and public resistance.
"Public acceptance of CCS in Germany is very low," Claudia Kemfert of the German Institute for Economic Research told DW. "No investment into coal CCS will be made, as there are other options like renewable energy."
Bio-energy carbon capture and storage
Some point out particular potential for special use of CCS in conjunction with biomass. The concept is based on dedicating large swaths of land to growing trees or shrubs, which essentially pull emissions out of the air because they need CO2 for their growth.
These plants are then later burned as biomass, thus producing energy. The carbon that is produced when the biomass is burned would then be captured and pressed into the ground with CCS technology.
Recapturing the CO2 produced is called "net-zero," referring to the fact that no carbon footprint would be left in the process.
The problem, apart from all the issues that come with the CCS technology, is that huge amounts of land would have to be earmarked for biomass. And this would hurt vulnerable groups like farmers in developing nations, or indigenous peoples who live off the land.
Carbon capture vs. renewables
In a report released earlier in 2015 criticizing the United States Environmental Protection Agency's support for CCS, Greenpeace said politicians and industry in favor of CCS "refuse to let go of the combustion economy, and waste valuable time and resources on false solutions."
Others argue that with so much of the world's economy dependent on fossils fuels, anything that can reduce their climate impact must be welcomed.
"If we have the technology to take CO2 out of fossil fuel use we should be ready to use it," said Lipponen. "I don't share the view that we should move away from fossil fuels just for the sake of it, if we can clean them up."
The Greenpeace report characterized CCS as a way to increase fossil fuel extraction, ultimately leading to more emissions. But it also attacked CCS on price, arguing that the cost of saving CO2 emissions through CCS is close to 40 percent more per kilogram compared with switching to photovoltiac solar power, and 125 percent more than wind power.
Spiraling costs, unknown risks
The world's major industrial CCS projects also proved hugely expensive. Norway, with its economy heavily reliant on oil and natural gas, has been a rare enthusiast for CCS in Europe. But its flagship Mongstad project was shut down in 2013 due to soaring costs and delays.
"The investigation shows that the complexity of implementing CCS was underestimated in 2006," Jorgen Kosmo, then Norway's auditor general, told media in 2013. "It has proven very difficult to plan and build capture facilities on a large scale. This has entailed high costs and a longer implementation period."
Due to these resulting cost increases, the auditor office's assessment was that the necessary investments could outweigh the benefits.
Both Canada's Boundary Dam project and one of America's biggest CCS projects - Kemper County - have also gone way over budget.
Lipponen admits that the price of CCS needs to come down, but says this is true of any new technology. The IEA believes CCS could be competitive in the power sector by the mid 2020s - but to get there, will require further research and development in addition to a meaningful carbon price.
Neither seems forthcoming in Europe at the moment.
Beyond costs, there are fears that the captured carbon may not stay below ground forever. Scientists have warned that Norway’s Sleipner CCS project, which stores carbon under the North Sea, could risk leakages through fractures in seabed rock.
And in Algeria, the In Salah CCS project had to be shut down in 2011 because the CO2 pumped underground was itself causing fractures in rock that was supposed to cap it below ground.
Lipponen says the UK's withdrawal of support from the technology represents a "total and sudden change of direction" from one of the few European countries to have shown commitment to the technology.
"It's disappointing, because this move will stop any large-scale industrial CCS projects going ahead in the UK for the foreseeable future," he told DW.