CARL SAGAN
‘THIRD-WAY’ technologies recreate, enhance or restore the processes that created the balance of greenhouse gases which existed prior to human interference, with the aim of drawing carbon, at scale, out of Earth’s atmosphere and/or oceans. It’s what plants, and a fair few rocks, do.
The pathways life has evolved to draw carbon out of the atmosphere and oceans are extraordinarily complex, and involve the magic of quantum mechanics. Their ultimate power source is the sun, which photosynthesis uses to take carbon dioxide and convert it into energy and solid matter, including the necessities we call food and fuel. Over an immensity of time, photosynthesis has remade our world. A breathable atmosphere, stupendous stores of fossil carbon, in the form of coal, oil and gas, and a non-toxic ocean, are all legacies of photosynthesis.
Although plants are an important component of the third way, it is about far more than plants alone. Technologies now exist that allow us to draw CO2 out of the air without the help of plants, and to make the captured gas into useful materials. Third-way approaches can involve the making of carbon-negative or carbon-neutral cement, changed management practices for livestock, and the manipulation of some natural geological processes, such as the weathering of certain kinds of rocks, as well as some very surprising new technologies.
My engagement with this fascinating basket of technologies and approaches began in 2007 when I received a phone call from Sir Richard Branson. He said that he had read The Weather Makers and that the book had changed his mind about the urgency of climate change. He invited me to Necker Island in the British Virgin Islands and confided that he was doubtful that humans could reduce emissions sufficiently fast to avoid catastrophe. He was planning to launch an innovation prize, calling for sustainable activities that have the potential to withdraw at least one gigatonne of carbon (about 3.7 gigatonnes of CO2—those oxygen atoms are heavy!) from the atmosphere per annum.
A gigatonne sounds like an enormous amount, and it is. In round figures, one gigatonne of carbon is about one-tenth of the volume of carbon pollution humans currently emit annually. An increasing number of predictions of humanity’s future emissions pathways suggest that Branson’s misgivings about our ability to avoid a climate disaster were prescient. Indeed, it is widely anticipated that if we are to stop short of 2°C of warming by 2100, humanity will need to be drawing many gigatonnes of carbon out of the atmosphere annually well before the end of the century.1 So, for the decades ahead, that’s the scale society needs to be working towards.
The £25 million Virgin Earth Challenge (VEC)—at the time the richest climate prize ever offered—was born from those ruminations. Branson asked me if I’d be a judge, and I agreed, joining Al Gore, James E. Hansen, James Lovelock and Sir Crispin Tickell. Over the years I’ve watched in astonishment as the applications rolled in. They have fundamentally altered my perception about how we might respond to the climate crisis. Back in 2007 the technologies and methods presented were rudimentary. As we draw closer to 2020, and as humanity’s carbon emissions levels continue to grow, some of the technologies encouraged by the Branson initiative have developed to look more and more like indispensable tools for our survival.
Moreover, it has recently become clear that drawing a gigatonne of carbon out of the atmosphere is just a beginning. The 2015 American Academies report on CO2 removal states that ‘reducing CO2 concentration by 1 ppm per year would require removing and sequestering CO2 at a rate of around 18 gigatonnes per year’. That’s around 4.8 gigatonnes of carbon annually—almost five times the VEC target. Reducing CO2 concentrations by 100 ppm (and so returning them close to what they were before the Industrial Revolution) would require removing around 1800 gigatonnes of CO2—the same amount that was added by human activity between 1750 and 2000.2
More than 10,000 submissions to the Virgin Earth Challenge have now been received. In 2011 these were pared down to a shortlist of 11 approaches. From restoring land and reversing ecosystem degradation to the capture of CO2 using resins, all 11 fall into two fundamental categories—biological and chemical—according to the ways they extract carbon from the atmosphere and/or the oceans.
Biological methods involve the removal of CO2 from the atmosphere or oceans via photosynthesis, and then storing the captured carbon in a variety of forms—from living forests to charcoal and plastics, or locking it deep in the earth’s crust. Chemical removal options use the weathering of rocks, or artificial means, to capture atmospheric carbon, and then sequester the carbon in a variety of places, some of which overlap with those utilised by the biological pathways.
These two categories differ in a fundamental way. The energy required to drive the biological processes is essentially free, being provided by the sun, via plants. This is a great advantage, but its flip side includes fundamental limits: the rate and volume of carbon able to be captured through biological pathways is dictated by the biosphere and its wonderfully reliable but relatively inefficient photosynthetic process. Photosynthesis is only 1 per cent efficient (it uses only 1 per cent of the sun’s energy available to it). Solar photovoltaic (PV), in contrast, can be 20 per cent efficient.
Quite apart from its limited efficiency, the biosphere is already bearing a heavy burden. We have cut down forests, polluted waters and driven to extinction many species. We are also placing great demands upon what remains of it for food, materials and space to live. And we continue to damage many of its unique and priceless ecosystems through ocean acidification and climate change, which limit our ability to use it for third-way approaches and technologies.
More ecologically grounded ways of managing and restoring the biosphere offer increasing promise as a means to reconcile the needs of the modern world while also restoring the natural world to function as it evolved to.3 There is great promise for work in this field to increase the carbon carrying capacity of ecosystems and soils.4 It can, however, be complex to work out what the right practices are in each unique set of species, soils and seas around the world, and to ensure effective stewardship of the system in question. Getting solid numbers behind the effects, such as the scale, longevity and permanence of carbon removal using biological approaches, is absolutely critical.
Any innovation can have negative as well as positive effects, depending on how it’s deployed, and there are ways that the biological measures could do more harm than good. For example, if people went after aggressively carbon-sequestering monocultures such as corn or sugar cane, or if we relied too heavily on storing carbon in biological stocks that may be destined to degrade because of changes already locked into the climate system, the long-term consequences could be severe.
The chemical category of technologies differ from the biological ones in that they all demand energy from human energy systems, either via electricity or the direct burning of fossil and other fuels, at some stage in the process. This is expensive, and until low-carbon, renewable sources become widespread, it has the disadvantage of adding to the problem (by burning fossil fuels) that it is trying to solve. On the other hand, many of the chemical technologies offer the advantage of both storing the carbon securely and/or creating something useful to humans in the process.
The option almost everybody thinks of when it comes to removing carbon from the atmosphere is to grow more trees. Trees, like all plants, grow by drawing in CO2. They are, in fact, little more than congealed atmospheric CO2, with half of their dry weight being composed of carbon drawn from the air. Many of the world’s forests have been cleared or degraded in recent centuries, so restoring them offers considerable potential for sequestration. But the scale of reafforestation required to draw down a gigatonne of carbon is staggering.
Trees grow over a long time, and start out very small, so we must take a 50-year time horizon as we think about this option. Over half a century, we would require an estimated 3–7.5 million square kilometres of land to be reforested (7.5 million square kilometres is roughly an area the size of Australia or the contiguous states of the US). We would need to complete between 70,000 and 150,000 square kilometres (approximately half the area of the United Kingdom) of plantings each year, if we were to sequester on average a gigatonne of carbon annually for fifty years this way.5 And the trees must be sustained for a century or more if the carbon is to stay out of the atmosphere for a useful period. Compared with many other third-way approaches, planting and maintaining trees is relatively cheap—reafforestation at this scale is estimated to be a modest US$20–$100 per tonne of CO2 captured and stored. But at $100 per tonne, it would still cost $370 billion to sequester a gigatonne of carbon by planting trees. Costs may well come down with scale, but there can be no doubt that they will remain substantial.
Of course, planting forests can bring other benefits, from water catchment protection to reducing erosion and the conservation of biodiversity. But there are potential downsides as well. As pointed out recently in Nature, reafforestation at this scale can have unintended consequences by changing Earth’s albedo.6 Trees absorb more heat energy than do paler grasses, and this increase in heat energy captured at Earth’s surface may offset, or even more than offset, any gains in reducing temperatures made by drawing all of that extra carbon out of the atmosphere. That’s not an argument against trees and their multitude of benefits, of course, but if we are reforesting for climate-change abatement, such factors need to be considered.
Carbon is stored directly in soils, in the form of humus, charcoal or the root mass of grasses. The amount and type of soil carbon can be influenced by land use. For example, cell grazing (where livestock are kept in a dense flock or herd, and moved from one paddock to another after grazing a small area for a day or so, mimicking the grazing patterns of the ancient roaming herds) may result in increases in soil carbon, partly by favouring perennial species with large root masses. The practice can also increase the stocking rate, potentially allowing soil carbon to be stored and a greater profit (and thus at a negative cost). Other methods of storing carbon in soils, however, can cost as much as $100 per tonne, at which price it would cost $370 billion to sequester a gigatonne of carbon. Prices, of course, are expected to decrease as industries scale up. But, nonetheless, cost is, at present at least, a formidable barrier.
Currently, there is a lack of precise science on how much carbon can be stored in soil using livestock management techniques and for how long. For the moment, investing in such programs for carbon storage is an uncertain business—a bit like buying a bag of rice without knowing how much rice the bag actually contains or its use-by date.
It is also possible to burn waste biomass, including garbage and forestry and farm waste, then capture the CO2 created, and store it deep in rock strata, a process known as Biological Carbon Capture and Storage (Bio-CCS). The only operational, commercial-scale Bio-CCS project in existence is the Midwest Geological Sequestration Consortium (MGSC). Located at the University of Illinois in the US, it is co-funded by government and industry. MGSC captures CO2 from ethanol production, which results in a relatively pure stream of CO2 compared with other types of biomass energy production (such as biochar). This minimises the cost of separating out the CO2. The captured and purified gas is then compressed and injected into a deep saline aquifer, where it is hoped it will remain permanently. The program is only economically feasible because of government research-and-development grants. A permit from the EPA is required, and because the process is ground-breaking technology, such permits are not easy to obtain.
The amount of carbon generated by burning biomass depends on many factors. But about half of dry plant matter is carbon, and 3.7 gigatonnes of CO2 includes 1 gigatonne of carbon. So you’d need to burn at least 2 gigatonnes of bone-dry feedstock such as sawdust to generate 1 gigatonne of carbon storable as CO2. Costs very much depend upon the future development of CCS technologies, but are likely to be higher than US$100 per tonne of CO2 stored ($370 per tonne of carbon stored). A cheaper alternative may be to store biomass as structural elements in buildings, or to bury it where it won’t break down and release CO2.
It’s worth looking at technologies based on processing trees and other land-based plants—to pick them apart a little in order to understand what might really be achieved—because humanity has more experience of this approach than any other.
Before the oil industry developed to its mammoth size, many of the products it generates today were extracted from wood. Indeed, for more than a century prior to World War II wood chemists had been creating myriad useful chemical products from timber. Lye, saltpetre and potash are age-old products derived from wood ash. They were used in cleaning, food preserving and explosives manufacture. Charcoal was also a useful fuel product, and the early wood chemists found that the process of making it yielded various valuable complex chemicals. The wood was burned in a low-oxygen environment (a process known as pyrolysis) and the fumes were captured and condensed in a copper still, and then decanted through a series of barrels and pipes. The result was a range of fuels, solvents, explosives, dyes, antifreezes, preservatives and early plastics such as bakelite. By the 1930s, wood chemistry had developed to such an extent that the industry was producing versions of most of the products that we derive from fossil fuels today.7
The impacts on the forests were substantial. An average wood chemistry plant in the northeast of the US consumed 11,232 cords of wood per year (a cord is 128 cubic feet, or 3.62 cubic metres)—enough timber, if stacked 1.2 metres high, to occupy 3.34 hectares.8 Forests were cut on a 30-year rotation. Shortly after World War II, the industry collapsed due to competition from fossil fuels, which were becoming available in bulk, and were transformable on a massive scale into fuels, fertilisers and plastics.
The climate problem has sparked renewed interest in wood chemistry. In 2008, a new research institute was set up within Hamburg’s Johann Heinrich von Thünen Institute, and various companies around the world are experimenting with this old technology. The production of alcohol is emerging as significant. The word alcohol has an intriguing etymology. It comes from Arabic—Al Kohl meaning ‘the powder’, as you might guess, from ‘kohl’, which has been used as eye makeup for thousands of years. But alcohol does not exist in powdered form. The link comes because alcohol must be distilled and, when distilling essences, the old alchemists often found a powdery residue in the bottom of their flasks, which they named Al Kohl, and which was later transferred to the distillate.
Today, a form of alcohol—methanol—is much used as a transport fuel. First-generation biofuel technologies source it from food products such as corn, and the carbon benefit over fossil fuels is marginal at best. But methanol made with second-generation technologies is now under development. Utilising the wizardry of the wood chemists, methanol will be derived from cellulose, resulting in a far larger carbon benefit (because tree farming takes less fossil fuels than growing corn).
The production of charcoal (biochar) remains the principal aim of many involved with modern wood chemistry, and from a climate perspective, biochar is the most important wood-chemistry product. Biochar is a relatively pure, mineralised form of carbon, so it rots very slowly in comparison with wood. If mixed in with the soil, or stored in old mines, it can be a secure carbon store for a century or more. As in traditional charcoal-making, the biochar process begins with heating vegetable matter (typically wood or wood offcuts) in the absence of oxygen. This separates the carbon-rich charcoal from the other compounds, which escape with the steam. It takes little energy, and is considered to be a carbon-negative technology because it allows for long-term storage of carbon that was captured from the atmosphere by plants. In recognition of its importance in addressing climate change, the technologies that produce biochar, and work through its complex interactions with the soil equivalent of a coral reef, are among the leading 11 technologies and approaches chosen as finalists in the Virgin Earth Challenge.
Biochar can be added to soils in ways that give additional benefits, such as moisture and nutrient retention. But the product takes many forms, depending on what it’s made from, and the temperature and speed at which it’s made. Some forms of biochar are good for some soil types, but other forms, particularly those made at high temperatures, can be toxic. Biochar science is complex—getting consistent quality of biochar out of a kiln and matching its characteristics with particular soil types are serious challenges.
The first-ever report summarising the state of the biochar industry was published in early 2014. Its chief finding is that the industry is in a very early stage, consisting mostly of small businesses in Europe and North America, selling biochar products locally for gardening and tree care. On average only 827 tonnes are sold per year, and because the price of biochar has yet to benefit from the economies of scale delivered by mass production, it remains relatively expensive—about US$2.50 per kilogram. Biochar companies range in scale from cottage industries to small-scale industrial concerns. The most important feedstock is waste from forestry, which tends to be centralised (for example, around sawmills), and therefore easy and cheap to collect.
Barriers to the industry’s expansion include a lack of financing, early stage technologies and a lack of demand for the product. The report states that education of stakeholders—from farmers to regulators and lenders—is the industry’s most urgent challenge.9
There are, however, other quite fundamental barriers. Given variation in soil types the biochar may be stored in, feedstocks and processes, it is not yet possible to predict how much carbon will be sequestered and for how long. This limits the ability of farmers using biochar to enter carbon markets. These constraints may be overcome soon, however, because scientific research into biochar continues to expand rapidly. The number of peer-reviewed biocharrelated publications increased nearly fivefold between 2009 and 2014, with over 380 papers published in 2013 alone.10
Biochar would need to be made and stored on a truly massive scale to meet the gigatonne-scale ambitions of the Virgin Earth Challenge. For example, theoretically, all of the agricultural and forestry waste in the world would need to be made into charcoal, as well as the yield of 100 million hectares of land growing energy crops, to sequester just one gigatonne of carbon per year. The challenge of mass production is compounded by the fact that agricultural waste is something of a misnomer. Much of the material that could be made into biochar is already used on farms to feed animals, as fuel for stoves, or as a soil conditioner.
Production costs presently range from zero to about US$60 per tonne, depending on feedstock and context. There are so many feedstocks, and so many soil types, that it hardly seems possible that biochar production could ever become a highly industrialised process producing gigatonnes of uniform and, therefore, inexpensive product. On the positive side, the biochar market is segmenting in interesting ways. Full Circle Biochar is a company that has focused on the consistent production of certain kinds of biochar, in the hope that the technologies it develops can then be licensed to large-scale manufacturers. The Biochar Company, in contrast, has focused on brand creation. Its product, Soil Reef, is tailored for the sequestration of carbon and the agricultural benefits of biochar.
Other companies produce biochar as part of wider operations. Phoenix Energy, for example, designs and builds small-scale (0.5 to 2 megawatt) power plants fuelled by biomass. They turn wood waste, agricultural waste and other biological waste products into a burnable gas, which is used to generate electricity and produce biochar, which is sold to farmers and gardeners, providing an additional revenue stream.
Cool Planet Energy Systems focuses on biofuel production, with the biochar by-product again providing additional income. With US$100 million in equity, it is one of the more mature companies in the biochar space. The biofuel that Cool Planet Energy Systems produces can be blended with petrol. The greenhouse gas saving comes from the fact that waste that would otherwise end up as CO2 is converted into biochar and a fuel that competes with fossil fuels. The company claims that its product performs as well as petrol, and can be sold at a similar price. In common with most other kinds of biochar, their biochar by-product can be stored in agricultural lands, where it can help retain biodiversity, and enhance soil moisture retention. In 2014, broadcaster CNBC listed Cool Planet Energy Systems, based in Denver, Colorado, as one of its top-50 disruptor companies.11
For all the advances being made by the various companies, biochar remains far from a planet-saving technology. The problem is scale. In order to sequester a gigatonne of carbon, long-term, in the soil in the form of biochar, up to eight gigatonnes of dry biomass may be needed. This is in part because biochar slowly degrades over time. The rate at which it degrades depends on soil and moisture conditions, but even in the best case only a portion of the carbon fixed as biochar during the pyrolysis process will be sequestered for more than a century. The industry has a long way to go before it is contributing significantly to the production of biofuels and the sequestration of carbon. But, as one of the most mature industries in a nascent field, it’s important in our fight to stabilise the climate. Indeed in a decade or two it may have transformed into one of the leading solutions.
So far, all of these options are land-based. When we turn to the waters, both the potential and the uncertainty increases. An important fact to recognise, however, is that the marine technologies can offer an almost immediate fix, at least in limited areas, to the ominous problem of ocean acidification.
Wetlands are spectacularly good at capturing CO2 from the atmosphere. Wetland plants grow fast, and the oxygen-poor conditions in many wetland sediments are ideal for storing carbon. Indeed many fossil fuels were formed in wetlands. Unfortunately, the world’s wetlands, from mangroves to saltmarshes, have suffered enormous degradation in recent centuries. Many have been converted to dry land for a variety of uses, including pasture and cropland, golf courses, canal estates and industrial areas. In addition, some are lost inadvertently due to developments upstream, such as dams, which starve them of their water supply. But some degraded wetlands could be restored. Just how much CO2 could be captured, and for how long, by restoring wetlands remains highly uncertain. Estimated costs of wetland restoration vary hugely—from US$10 to $100 per tonne of carbon captured.
The most exciting, if least understood, of all options concerns the cultivation of seaweed. While still very much a frontier prospect, if indeed not just beyond the horizon, the potential of this approach is enormous. The stupendous potential scale of seaweed farming was outlined in 2012 by Dr Antoine De Ramon N’Yeurt of the University of the South Pacific and his colleagues. They explain that because seaweed grows very fast, seaweed farms could be used to absorb CO2 very efficiently, and at a large scale. The seaweed could be harvested and processed to generate methane for electricity production or to replace natural gas, and the nutrients left could be recycled.12
Their analysis shows that growing seaweed could produce 12 gigatonnes per year of methane, while storing 19 gigatonnes of CO2 that result from the methane production. A further 34 gigatonnes per year of CO2 could be captured if the methane is burned to generate electricity.
These rates are based on macro-algae forests covering 9 per cent of the world’s ocean surface, which could produce sufficient biomethane to replace all of today’s needs in fossil fuel energy, while removing 53 billion tonnes of CO2 per year from the atmosphere . . . This amount of biomass could also increase sustainable fish production to potentially provide 200 kilograms per year, per person, for 10 billion people. Additional benefits are reduction in ocean acidification and increased ocean primary productivity and biodiversity.13
Many of the technologies required to achieve this are already in widespread use, if at a comparatively minuscule scale. Indeed, seaweed farming covers hundreds of square kilometres off the coast of China alone. The required methane digesters are also a simple technology, which is widespread in agricultural use to transform waste such as piggery effluent, and could easily be utilised on floating factories.
Where would all the CO2 be stored? N’Yeurt and his colleagues give four possible options, one of which is Carbon Capture and Storage in the ocean floor. Importantly, as we shall soon see, CO2 storage in marine sediments at depths below 3000 metres is looking like a much more favourable prospect than geosequestration on land.
In its scale, efficiency and potential advantages, seaweed farming may provide spectacular solutions to the climate crisis. Covering 9 per cent of the world’s oceans with seaweed farms, and then processing the voluminous product yielded, is far beyond our current capabilities. It is heartening to think, however, that no new technologies are required for this approach and that, by itself, it comes close to being able to negate our current global emissions.