Going underground

Friday 28 August 2020

Governments and industry hope it will be possible to go on pumping out carbon as long as we bury it later. It will be – at a price

Imagine you could put the entirety of the human race, and all the ecosystems we depend on, in a normal-sized bath. You are adding a 20-litre bucket of water to the bath every minute and are aiming to stop adding water in half an hour by slowly reducing to zero the amount you put in the bucket each time. However, at your current rate, you will drown everyone in 12 and a half minutes, when you fill the bathtub. But wait, you have a plan. You are going to remove water by half a mug full, each minute, too. Unfortunately, this won’t be enough.

Why this story?

If we can’t prevent all carbon emissions, could we bury them? In principle there’s plenty of room in porous rocks and underground cavities, including those left by oil and gas exploration. In practice the idea is horribly expensive.

Despite this, policymakers have a soft spot for CCS (carbon capture and sequestration). Niamh Ryall ran the numbers to see if it could ever pay off. Giles Whittell, editor

You can either invest in a slightly bigger mug, at great expense, or add less water to the bath. This is the current state of CCS and global carbon emissions.

CCS stands for carbon capture and sequestration; the business of separating CO2 from the gases pumped out by, say, a coal-fired power station, and pumping it deep underground so that it never warms the atmosphere. Big carbon polluters swear by CCS as a way of achieving carbon neutrality while still polluting. But it doesn’t operate commercially yet anywhere in the world, and in many places where CCS plants are up and running their main function is to produce more carbon: 19 of the 23 operating CCS plants globally are made viable by using the carbon dioxide they produce to recover more oil from oil wells.

Carbon dioxide from the Petra Nova CCS plant in Texas is taken from a coal-fired power station’s emissions – and used to boost oil production at nearby wells

Boris Johnson, the UK’s prime minister, said in February that he hoped 2020 would be a “defining year of action for our country, and indeed for the planet, on tackling climate change”. The following month his government announced £800 million of funding for CCS.

It was at least a start. Most CCS technologies pull CO2 out of the air by bubbling it through a material that the CO2 sticks to, then heating the material up to yield a pure CO2 stream. Then it is transported and pumped into the earth. When emissions from capturing and transporting the CO2 are lower than that captured, it is “carbon negative”, resulting in a net removal of carbon dioxide from the air.

This makes CCS a negative emissions strategy, and the scale of the climate crisis means negative emissions feature in the vast majority of scenarios designed to limit warming to 1.5 °C by the end of the century. They are needed at scale within 30 years, because achieving zero emissions alone is no longer enough for a habitable planet for many people.

Negative emissions and geoengineering

In 1816 Mary Shelley was enduring a terrible summer holiday. Geneva was cold and gloomy, and the lake was swept by storms and biting winds. Shelley retreated indoors and penned the tale of Frankenstein, the crazed scientist who tried to play God and created a monster. Little did she know that the ‘Year without a Summer’ had been caused by the massive eruption of Mount Tambora in the Dutch East Indies. Vast quantities of ash and gas had been ejected into the stratosphere where it dimmed the sunlight reaching the planet. We can only guess what Shelley would have made of geoengineering, one branch of which proposes deliberately creating a similar ‘volcanic winter’ to counteract global warming. 

Human intervention in the global climatic system has long been regarded as fringe science at best. Many have argued that geoengineering holds unknown risks and that unintended consequences could trigger catastrophe. But isn’t that exactly what we are doing already with our reckless carbon emissions? Global warming is already a Frankenstein of our own making. Maybe we fear having to change our behaviour or maybe we fear what we have already done. Critics say geoengineering should only be used as a last resort, but proponents counter we have already reached that point.

Direct Air Capture

Machines draw ambient air through filters which chemically absorb the carbon dioxide. Heat releases the gas, which can then be stored underground. There is little demand for the CO2 itself, which highlights the solution’s economic downsides. The process can currently cost over $200 per tonne (compared with $10 per tonne through planting trees) but start-ups such as Climeworks of Switzerland and Carbon Engineering of Canada believe costs will fall with scale.

Stratospheric Shrouding 

Volcanoes can reduce global temperatures by ejecting sulphate aerosols into the stratosphere where they prevent some solar radiation reaching the surface of the earth. Shrouding proposes artificially injecting gases such as hydrogen sulphide and sulphur dioxide into the high atmosphere to achieve the same effect. Getting the aerosols into the stratosphere using aircraft would be highly counterproductive in terms of carbon emissions so it is proposed that aerosols could be introduced by airships or tethered balloons.

Cloud Brightening

Spraying a fine mist of sea salt particles into the lower layers of clouds, especially over the oceans, would promote the formation of droplets and increase cloud cover. This would result in more solar radiation being reflected into space by the brighter clouds and a cooling of the surface temperature. In Arctic regions where the disappearance of sea ice is resulting in more heat being absorbed by the darker sea surface, advocates propose spraying the salt particles from towers on floating platforms.

Ocean iron fertilisation

This solution envisages dispersing iron aerosols into the ocean to promote the development of algae blooms. As the algae grows it absorbs carbon dioxide from the atmosphere. When the algal blooms die, they sink to the ocean floor and the carbon they contain is locked into deep ocean sediments. Supporters say the process could also boost fish stocks. Others say changing the chemical composition of surface waters could increase greenhouse gas emissions.

Each of these proposals has huge drawbacks – the enormous cost; the geopolitical challenge; the environmental side effects and the unknown outcomes from altering the global climatic balance. But perhaps the greatest drawback is the idea that we can continue to ignore the cause – carbon emissions – by seeking to only treat the symptoms. A fundamental moral hazard lies at the heart of geoengineering. Having created a monster, it’s perhaps foolish to think we can deal with the consequences without risk.

James Whyte

The problem is not the technology, which is proven, nor the sites, which have a theoretical capacity many times what is needed. The problem is cost.

CCS will need to be profitable eventually. It is nowhere near that now. The only CCS technology the UK currently has at scale – and the version favoured by the Intergovernmental Panel on Climate Change (IPCC) – captures its CO2 from carbon-neutral biofuel and buries that, ensuring that the whole process is carbon-negative. This is bioenergy CCS, or BECCS, and cost estimates for CO2 from BECCS vary worldwide between £88 and £288 per tonne.

That’s not cheap. If CO2 were valuable this wouldn’t be a problem, but it’s not. There are niche uses of pure, concentrated CO2, such as in fizzy drinks, but these don’t sequester it for long. Otherwise it’s largely useless. So CCS is essentially capturing waste, which is not a problem not shared by solar or wind energy. Without the certainty of a price for sequestered carbon, CCS is not an investment. Given the energy intensity of most CCS processes, it also needs a lot of carbon neutral energy to prevent emissions being higher than the CO2 captured.

Equinor (formerly Statoil) plans to start burying carbon off Norway’s west coast

This is the context in which the UK’s investment in CCS needs to be viewed. Using the entire £800 million investment, and presuming a charitable estimate of £80 per tonne of CO2, we could mitigate about 10 million tonnes of CO2. That is, 10 million of the 350 million tonnes the UK will emit this year. As this is negligible, it’s fair to assume the intention must be an investment in a technology expected to be made viable in the future by a high carbon tax or a rebooted system of carbon cap-and-trade.

This wouldn’t necessarily be a foolish use of money. Under current UK plans for net zero emissions by 2050, 130 million tonnes a year would have to be sequestered one way or another, so investment to bring down the price of CCS through R & D or economies of scale, or both, could pay off in the end.

But there’s a snag. At a carbon price increasing to over £80 per tonne a raft of other technologies become viable, and CCS may find it hard to compete with them. Even without such a price, electric vehicles, recycling and efficiency gains in domestic heating all offer a net return on investment (not to mention improved homes, less pollution and jobs in retrofitting). As we start paying in earnest for carbon emission reductions it will become cost-effective to convert land to new pasture methods that fix more carbon; to invest more heavily in nuclear, wind and solar energy; and only then to invest in CCS as a climate mitigation option. Over their lifetime, renewable energy plants with energy storage systems are already cheaper than coal-with-CCS in the three largest coal consuming nations (India, China and the US).

The up-front costs of CCS are in the middle of the options available but other costs, harder to quantify, have to be taken into account. One of the most significant of these is competition for land. Broadly, to make a reality of BECCS, pastureland will need to be converted on a huge scale.

Last year’s IPCC special report on limiting warming to 1.5 °C required 3.7 million tonnes of CO2 per year to be sequestered with BECCS. That would use 25-80 per cent of current cropland and would need an increase in forest cover equivalent to three times the size of the UK in the next 10 years.

There are methods of CCS that require less land. Enhanced weathering is one that involves crushing rock and spreading it on land or in the sea. Direct air capture (DAC) uses big fans to suck air through CO2-absorbing materials. But using current DAC technology and our current energy system make-up, the energy cost of capturing one year’s emissions would be about 114 per cent of total global energy consumption, emitting more than was captured in the process.

Iceland’s Hellisheidi Reykjavik Energy plant has plans collect more carbon than it emits by injecting it into basalt rock and collecting it with direct air capture machines.

Reports abound of CO2’s redemption as a useful product. The unfortunate truth is that it is hard to get CO2 to do anything without expensive technology, vast amounts of energy or both. It will be necessary to find new ways of using it in concrete and plastics as we avoid fossil fuel products, but these processes are likely to remain more expensive than using other products without a fair price for emissions.

The UK is not the only country investing in incentives for CCS. The US is investing $260m over 12 years, having already invested $4bn in the past two decades, which can be claimed by anyone producing at least half a tonne of CO2 a year. You can even claim this money at 70 per cent of the full rate for using the CO2 to recover more oil.

The reality is that CCS can only be part of the picture, and without a proper carbon price it will remain unviable. The UK’s argument for CCS given its cost in money and energy is inadvertently an argument for reduced emissions, abundant sustainable energy and any funding mechanism that enables this transition to happen.

But the government already knew that.

Photographs Getty Images, Illustrations by Lizzie Lomax