In May last year, a scientific curiosity opened in Zurich. A company called Climeworks set up the first commercial plant designed to remove carbon dioxide (CO2) directly from the air. This idea has been floating around for a number of decades as a method to reduce atmospheric CO2 concentrations and avoid climate change, and is now gaining increasing traction among some institutions and academics.
This particular plant can only capture about 900 tons annually, a far cry from the 35,000,000,000 tons (or 35Gt) annually emitted from anthropogenic sources. It needs to scale up. But is it scalable, or is it a fantasy to think so? The question stands: are plants like these and other negative emissions technologies (NETs) a necessary component of climate change mitigation, or a dangerous distraction from the real work needed?
The Climeworks plant is based on direct air carbon capture and storage (DACCS), a spin-off from the more well-known carbon capture and storage (CCS) technologies installed at large point emissions sources like power plants. In DACCS, air from the atmosphere flows directly over a man-made filter that selectively removes CO2. This carbon-depleted air is then returned to the atmosphere, while the filter is regenerated by releasing the CO2 in a concentrated stream either for disposal or use.
The filter, which can be liquid or solid, is key to getting DACCS right, and must be extremely efficient to be useful – CO2 molecules currently make about 0.04% of all in the atmosphere. Efficiency and cost are the biggest downsides of this technology – in 2011 it was estimated that with current filters, a 10m high, 30km long DACCS plant would be needed to catch the emissions of a single typical coal plant. It’s thought now that DACCS’s capacity for removal is at least 3.3Gt per year, although this may well change as the technology advances.
DACCS is only one of a number of negative emissions technologies. Another that also relies on carbon capture technology is bioenergy with carbon capture and storage (BECCS). This entails replacing fossil fuels with energy crops such as fast-growing perennial grasses or forest biomass, burning it to generate thermal energy in the same fashion as fossil fuels, and capturing the released CO2. As these crops grow they will naturally remove CO2 from the air through photosynthesis, and when they are burned the carbon won’t be released into the atmosphere, giving a net negative emissions effect.
An advantage is that this method builds on existing technologies – energy from biomass is advancing and there are some conventional CCS plants already operational. But neither technology is efficient enough yet, and enormous land areas would be needed to grow enough biomass to reach the gigatonne scale needed. This will have knock-on effects – existing carbon stocks will be disrupted, the land used may compete with food crops and reforestation projects, and ecosystems may suffer. Right now BECCS could remove 3.3Gt per year, and this probably doesn’t have as much space to grow as DACCS.
A final common method is ocean iron fertilization (OIF). Plankton and other microscopic plants take up CO2and convert it into organic matter. Some of this sinks and is sequestered by the deep ocean, where it mostly stays. The idea behind OIF is to enhance this process by adding certain nutrients to boost planktonic growth, and therefore to take more carbon out of the atmosphere. The advantage here is that it uses a natural process and won’t require great technological breakthroughs.
There are numerous drawbacks, however, which will limit its use. When iron is added to an ecosystem it can’t be targeted and it can’t be controlled which organisms will benefit. There have been numerous cases of this technique stimulating harmful toxic algal blooms, and on a larger scale this could have dangerous and unpredictable consequences spreading throughout an ecosystem. Also its potential for capturing carbon is unspectacular, with an estimated upper limit of 1GtC per year.
There is a strong case for expanding the use of NETs and increasing research funding. Generally in mitigation strategies decided at international conferences, leaders decide that climate change is to be countered either through new renewable technologies or government-led changes encouraging a low-carbon lifestyle. But so far, both of these strategies have led to disappointing results.
The Kyoto Protocol was the flagship international treaty for tackling climate change, and was negotiated and advocated with much vigour and optimism. It was initially signed in 1997, but only became effective in 2005 because not enough countries had ratified it domestically. The mechanisms for emissions reductions included carbon caps, investment in renewables and forest management, although much of this was left up to the individual nations.
Industrialised countries were expected to make an 8% reduction in emissions from 1990 to 2020, but the Intergovernmental Panel on Climate Change (IPPC) has estimated that a 10-40% reduction is necessary to meet the 2°C target. Even those modest targets won’t be met, and overall global emissions rose 31% from 1990-2010. Some contend that Kyoto didn’t work because it didn’t cover enough of the world and largely left out developing countries, and that the Paris Agreement has sufficiently broader coverage to bring about the cuts needed.
However, the Climate Action Tracker that assesses countries’ targets and charts their progress tells a different story. Only seven countries are 2°C compatible, current pledges would lead to approximately a 3.2°C rise, and current policies leave us on course for a 3.4°C rise. So far, then, traditional mitigation has been lacking. It’s unrealistic to expect us to stop burning fossil fuels anytime soon, and it’s possible that we’ll need to figure out how to get their emissions out of the air someday, the sooner the better. The IPPC has begun factoring in NETs to its pathways for getting emissions down to an acceptable level.
There is staunch opposition to this argument, however, on a number of grounds. Most salient is the possible side-effects. BECCS and OIF are certain to have some undesirable knock-on effects (toxic blooms and land made unusable for anything else), and may potentially have disastrous consequences for the ecosystems they’re implemented in – it might be better to take a precautionary approach and avoid damaging an ecosystem. DACCS will likely have fewer side-effects but may affect the surrounding vegetation by depriving it of CO2. And though it has modest side-effects compared to other NETs, it’s also the one that furthest from implementation.
Renewables were depended on as the technology that will save us from high emissions but progress so far has not been fast enough. NETs are a bet in the same way – there is no reason to expect this technology to take off when others didn’t. And reliance on it as a “silver bullet” is a real threat. If we think we can pollute without consequence and emit what we like now because it can be cleaned up later, we might not make the efforts in other areas to cut emissions.
Particularly if NETs don’t develop as anticipated, the net effect could be increased emissions. “Clean coal”, a proposed coal fuel where CCS and other technologies would be so advanced that we could burn fossil fuels and strip out all the carbon, provides a cautionary tale. It was a hot topic about a decade ago and absorbed a lot of funding and time (unsurprisingly, it hasn’t worked yet). Indeed, a recent report from the European Academies Science Advisory Council recently warned that technologies to remove CO2 from the air will not have the capacity to be a ultimate solution, and to think they ever could is very dangerous. Maybe what we need is deep, structural change to aggressively cut down on carbon, and that the last thing we need is a distraction like this.
What do with do with the technologies then? A lot of these criticisms are strong, and NETs shouldn’t be relied on as a fixer. Excessive focus on any one mechanism to counter climate change is likely to mislead us and be damaging. The risk of any possible side effects, too, should make us hesitant about making large-scale interventions in ecosystems. But these are notes of caution, not fatal points against ever using the technologies.
There is a range of measures we need to take – alternative energy sources, emissions caps, land use change – and negative emissions should take its place among them. Even if we were to bring emissions to zero today, the gases currently polluting our atmosphere would make temperatures and sea level rise for decades, centuries if we’re very unlucky. Many experts see no way ahead without them, and international institutions like the EU are beginning to make noises in its favour. The prospect of practicable negative emissions is a bet, and one that we may have no choice but to make.