Extract Three: Wadhams on Geoengineering and other Drastic Measures

Third Extract from Chapter 13 of Wadhams’ Book: Drastic Solutions

Geoengineering

“[…] Geoengineering comprises a suite of techniques to artificially lower surface air temperatures, either by blocking the sun’s rays directly or by increasing the albedo of the planet so as to change the radiation balance. For the Arctic, the aim of both SRM and CDR must be to bring back the ice that we’ve lost, and in this way halt the loss of offshore permafrost and reduce the likelihood of a giant methane release. To achieve this, we need to not merely slow the pace of warming, but to reverse it. Let us look at the different ideas proposed, how effective they are likely to be, and the political difficulties.

SRM is the rapid ‘sticking plaster’ which can be implemented quickly at moderate cost. It does not deal with CO₂ levels, and so phenomena such as acidification of the oceans, which depend mainly on CO₂ levels rather than temperature, will continue apace, with serious consequences for bleaching of coral reefs, for shellfish survival, and in fact for the entire marine ecosystem. So SRM does not let us off the hook about reducing CO₂ levels as well.

Two major types of SRM methods have been proposed to date. In 1990 John Latham at the University of Manchester proposed ‘whitening’ low-level clouds by injecting very fine sprays of water particles into them. This increases the cloud albedo and causes them to reflect more incoming solar radiation. The brilliant marine engineer Stephen Salter at Edinburgh University designed the systems to carry out this injection. Others have proposed the injection of solid particles at high elevations from balloons or jet aircraft afterburners, which would form aerosols that reflect incoming radiation.

Marine cloud brightening (MCB) involves increasing the amount of sunlight reflected back into space from the tops of thin, low-level clouds (marine stratocumuli, which cover about a quarter of the world’s oceanic surface), thereby producing a cooling effect. If we could increase the reflectivity by about 3 per cent, it is estimated that the cooling will balance the global warming caused by increasing CO­­₂ in the atmosphere. To do this we need to spray sea-water droplets continuously into the cloud. Salter developed plans for a novel form of spray-droplet production, and designed an unmanned wind-powered vessel that can be remotely guided to regions where cloud seeding is most favourable. Instead of sails, such a vessel could use a much more efficient motive power technique – Flettner rotors. These spinning vertical cylinders mounted on the deck are named after their inventor, the German Anton Flettner, and make use of the Magnus effect, whereby a spinning vertical cylinder has a pressure difference across its sides which gives force at right angle to the wind direction. Flettner rotors were used for ships in the 1920s and have been revived today as a way of reducing fuel consumption at sea. The rotorship houses the spraying system which sprays sea water droplets from the top of the rotors into the cloud base. The power required for spraying and communications comes from electricity generated by current turbines built into the vessels. The key to the design is the fine nozzle which produces particles o the required diameter of about a micrometre (a millionth of a metre), such that when the droplet evaporates in the atmosphere it produces a tiny salt particle which is of just the right diameter (a nanometre or so) to brighten the cloud. This makes use of the so-called Twomey effect, that a mass of tiny particles in a cloud is brighter than the same mass of larger particles. This effect has been observed from ships leaving the equivalent of a con-trail of brighter clouds, visible from space. Several hundred vessels distributed worldwide would be needed to achieve the aim, but the total cost, while substantial, is small compared to the massive costs of global warming to the planet – billions of dollars per year compared to global warming costs of trillions. A huge advantage of the plan is that it is ecologically benign, the only raw material required being sea water. The amount of cooling could be controlled, via satellite measurements and a computer model, and if an emergency arose, the system could be switched off, with conditions returning to normal within a few days.

Much work is needed before a cloud brightening system could be operational. We would have to complete the development of the technology, and conduct a limited-area field experiment in which the reflectivity of seeded clouds is compared with that of adjacent unseeded ones. We would also have to perform detailed analyses to establish whether there might be serious or harmful metereological or climatological ramifications (such as reducing rainfall in regions where water is scarce) and, if so, to find a solution for them. One question is, must we spray worldwide and thus achieve global effects or, if we specifically desire a regional outcome, can we spray in particular locations or at particular times of year? The very urgent question of cooling the Arctic comes to mind. If it is the open water over the Arctic shelves in summer which allows warming of the subsea permafrost and a potential methane catastrophe, can we stand this off by bringing back the summer sea ice without necessarily having to cool the entire planet?

This regional question was tackled by John Latham and colleagues in 2014. We found that indeed it is possible to focus the cooling on the Arctic and cause some advance in the sea ice limits, especially in the Beaufort and Chukchi seas, although there may be compensating problems such as reduction of rainfall in sub-Saharan Africa. Clearly this is cautiously promising. In an earlier study, it was estimated that spraying over 70 per cent of the marine global cloud cover could eliminate the warming due to CO₂ doubling and halt losses of sea ice. The cloud brightening is basically reducing the radiation falling on the ocean surface, so, if regionally targeted, this might also have beneficial effects in reducing the vigour of hurricanes (which depend on sea surface temperature) and the rate of bleaching of coral reefs (which depend on water temperature as well as ocean acidity). Finally the Antarctic sea ice could also be affected: the 2014 study showed that global seeding will increase the Antarctic sea ice area and also cool the subsurface currents which at present are threatening to cause the Thwaites and Pine Island glaciers to collapse, which could cause a serious, 3-metre rise in global sea level if it occurred suddenly. So MCB may offer not only global relief with respect to warming, but also relief from regional threats, especially in the polar regions.

Stephen Salter mapped out a development plan which estimates that taking a cloud brightening system to full operational effectiveness would cost £73 million in research and development costs, a fortune in terms of normal science budgets but a pittance in terms of the urgent global need. If Britain were serious about fighting global change, this would be an area where it could take a lead.

Aerosol injection is the second large-scale geoengineering method that has been proposed. Some of the implications were studied in a recent project supported by the UK Government called SPICE (Stratospheric Particle Injection for Climate Engineering), although support was withdrawn before the scientists could actually try a system out. The idea is to disperse a large mass of aerosols, tiny particles, into the stratosphere at high level, so that they can directly reflect sunlight back into space. The injection would have to be continuous, as the aerosol gradually falls out of the upper atmosphere. The original ideas called for the creation of a stratospheric sulphate aerosol cloud, either through the release of a so-called precursor gas – sulphur dioxide (SO₂) – or through the direct release of sulphuric acid (H₂SO₄). If SO₂ gas is released it will oxidize in the upper atmosphere and dissolve in water to form sulphuric acid in droplets far from the injection site. This does not allow control over the size of the particles that are formed but the gas is fairly easy to release. If sulphuric acid is released directly then the aerosol particles would form very quickly and, in principle, the particle size could be controlled to optimize the climatic effect. If the aerosol is injected onto the lower stratosphere it will remain aloft only for a few weeks or months, as air in this region is predominantly descending, so to ensure a longer lifetime of years, higher-altitude delivery is needed.

How might this be done? Delivery systems suggested include artillery shells, high-altitude aircraft, or high-altitude balloons, either supporting vertical pipes from the ground or rising freely until they burst, with the precursor gas inside them. The cheapest systems appear to be existing tanker aircraft such as the US KC-135 or KC-10 military tankers, only nine of the larger KC-10 aircraft being required to deliver 1 Teragram (1 million tons) of sulphur dioxide per year at three flights per day. Sixteen-inch artillery shells are comparable in cost, as are a huge number of small balloons in which hydrogen sulphide (H₂S), another possible precursor gas, is mixed with hydrogen to give a buoyant balloon which bursts when it reaches the stratosphere; 37,000 commercial balloons would be needed per year. The systems are simpler than for marine cloud brightening, but the quantities involved are very large and the chemicals have to be hoisted high into the atmosphere.

We know that high-altitude particles can indeed affect climate, because of volcanic eruptions – the eruption of Mount Pinatubo in 1991, for example, produced a noticeable global cooling for three years afterwards. The cost would be within bounds, being estimated as 25-50 billion dollars per year to fully counteract Man’s additions of carbon dioxide, according to Paul Crutzen who was an early proponent of this idea. However, many potential problems have been identified. Rainfall would be reduced, which might have a serious impact on the Asian and African monsoons; there might be an increase in the rate of ozone destruction, leading to a regrowth of the ozone hole; it is difficult to predict how the cooling will be distributed worldwide, so some countries may experience less cooling than others, or even warming, and so on. Behind it all lies an unease with the idea of injecting large quantities of an undeniably toxic chemical into the upper atmosphere; marine cloud brightening with sea water particles sounds positively benign by comparison. One relentless opponent of aerosol injection, Alan Robock of Rutgers University, has recently changed his views, however; he co-authored a 2016 paper which showed that the aerosol cloud would not only reduce direct radiation reaching the ground, it would enhance diffuse radiation, which would combine with the cooling to produce an increase in plant photosynthesis rates. This increase in plant growth would itself play a role in reducing carbon dioxide levels in the atmosphere, an unexpected extra benefit.

A few other geoengineering techniques have been proposed. One is the space reflector, a very large mirror or system of mirrors in orbit, to reflect large amounts of sunlight into space. However, nobody has come up with a feasible plan that could assemble anything like this in orbit at anything other than colossal cost.

Carbon drawdown

I have explained why carbon emission reduction is unlikely to happen, at least not fast enough, and if it is done slowly, as it will be, it will leave a legacy of excess CO₂ in the atmosphere which will continue to drive future warming. Geoengineering can counteract the impact of carbon dioxide and methane on the atmosphere, but at the cost of leaving the CO₂ to continue tis work in acidifying the ocean, which could ultimately destroy our marine ecosystem (and thus our global ecosystem, since the ocean makes up 72 per cent of the planet’s surface area). My bleak conclusion is that in the end (and that end may be close) we have to find a way of taking CO₂out of our planetary system if we are to defeat global warming and save our civilization. How do we do it?

First of all, we must take the whole problem seriously. In fact, if it the most serious question facing the world – can we bring ourselves back from the brink of runaway climate change and retain the basis of viable life for the humane race? Or must we grapple hopelessly with accelerating climate change which makes large parts of the planet unlivable? In this respect one of the most shameful failures has been that of the IPCC. In its Fifth Assessment report in 2013, the IPCC recognized that the only way to a viable climate is to follow the RCP2.6 route. I have already expressed my suspicion that the ‘RCP’ formulation of radiative forcing conceals the realities of what is needed to avoid disastrous climate change. But the result is a paradox, unstressed by the IPCC: the only way to save ourselves is to follow the RCP2.6 route, and the only way to do that is to actually take CO₂ out of the atmosphere, since we will very shortly reach the CO_­2 concentration (421ppm) which is the ceiling for ‘acceptable’ climate warming. We are certain to pass that limit without even noticing it in about a decade, so fast are CO₂ levels rising, and beyond that point our only hope is actual carbon removal. The IPCC knows this but ignores the problem of how we might actually remove CO_2. A further crucial component of CO₂ removal is the impact that large-scale application of it could have on ecosystems and biodiversity. This has to be studied on an international scale before we begin attempts at large-scaled CO₂ removal; again, this is ignored by the IPCC.

Two possible techniques have assumed prominence recently. They are bioenergy with carbon capture and storage (BECCS), and afforestation. BECCS involves growing bioenergy crops, from grasses to trees; burning them in power stations; stripping the CO₂ from the resulting waste gases; and compressing the gas into a liquid for underground storage. Afforestation – planting trees – also relies on photosynthesis to remove CO₂ from the atmosphere; storage is achieved naturally, in timber and soil. If we are to limit the global temperature rise to 2^oC, we need to remove some 600 gigatons of CO₂ by the end of this century. Using BECCS, this would require crops to be planted solely for the purpose of CO₂removal on between 430 million and 580 million hectares of land – around one-third of the current total arable land on the planet, or about half the land area of the United States. This is clearly impossible, unless we can achieve remarkable increases in agricultural productivity which greatly exceed the needs of a rapidly growing global population. It is more likely that we will need that arable land to feed people (and in any case it will probably be less productive because of the extreme weather effects arising from Arctic change). BECCS would have to use primary forest and natural grassland, which equally we cannot spare because afforestation is itself one of the possible ways of removing CO₂. These wild places also contain the last strongholds of vast numbers of threatened terrestrial species, the loss of which might be disastrous for the continued survival of the planetary ecosystem. A further fundamental concern is whether BECCS would be as effective as is assumed at stropping CO₂ from the atmosphere. Planting crops at such a scale could involve more release than uptake of greenhouse gases, at least initially, as a result of land clearance, soil disturbance and increased use of fertilizer. When such effects are taken into account, the maximum amount of CO₂ that can be removed by BECCS (under the RCP2.6 scenario) has been estimated to be 391 gigatons by 2100, about 34 per cent less than the amount assumed to be needed to keep the temperature rise below 2^oC. If less optimistic assumptions are made about where the land for bioenergy crops can come from, the net capture by 2100 comes down to 135 gigatons. So it already looks as if BECCS cannot do the job alone. On top of all this, we would be planting bioenergy crops into a world of changing climate: what will their water requirements be in a warmer world? How will they compete with food production if overpopulation really leads to a race for cropland? And (as with other techniques) how do we capture and where do we store the carbon dioxide?

Afforestation sounds a gentler way of taking CO₂ out of the atmosphere, since we don’t have to put it anywhere. Everyone assumes that an increased forest cover is environmentally desirable – even while we are busy chopping down the Amazon and Southeast Asian forests for their hardwoods and to grow soya beans or keep cattle. How do we grow more forest when all the pressure is towards forest loss? Afforestation can also involve the loss of natural ecosystems, if we are replacing natural forest by managed monospecies forests. We are only at the beginning of the proper study of key forest species whose loss could be disastrous either for preserving our global ecosystem, or for keeping down serious pests like the bark beetle. A third of new drugs are developed from forest plants. And planting swathes of managed forest will cause complex changes in cloud cover, albedo and the soil-water balance, through changes to evaporation and plant transpiration. One undesirable change is occurring with the northern boreal forest. With global warming the treeline is moving north, which one might think of as a good thing except that during the season of snow cover a terrain covered with tree foliage (bare branches or evergreen needles) is darker than flat snow-covered grassland or tundra, so the overall albedo is reduced and again there is a net warming effect. Systematic use of afforestation will involve cutting down the trees (and storing the wood) when they have reached a certain stage of growth, followed by replanting; this will not work if increased fires, droughts, pests and disease cause the trees to die and fall before harvesting.

Many other ideas have bene proposed for CO₂ removal by biological, geochemical and chemical means. For all such schemes, modelling theoretical potential can give a completely different picture from that obtained when environmental impacts – not to mention practicalities, governance and acceptability – are considered. A case in point is the long history of discussion, research and policymaking on ocean fertilization, another CO₂-removal technique. When a link was first made between natural changes in the input of dust to the ocean, ocean productivity and climatic conditions, there were high expectations of how effective ocean fertilization might be as a way to avoid human-driven global warming. During the 1990s, researchers postulated that for every ton of iron powder added to sea water, tens of thousands of tons of carbon (and hence CO₂) could be fixed by the resulting blooms of phytoplankton. This estimate has been whittled down over the years and after fourteen small-scale field experiments, with the realization that most of the CO_{2 ­}absorbed by such blooms – stimulated either by adding iron or other nutrients to sea water, or by enhancing upwelling through mechanical means – is released back into the atmosphere when the phytoplankton decompose. Moreover, a large-scale increase in plankton productivity in one region (across the Southern Ocean, say) could reduce the yields of fisheries elsewhere by depleting other nutrients, or increase the likelihood of mid-water deoxygenation. Such risks have resulted in the near-universal rejection of ocean fertilization as a climate intervention, through bodies such as the Convention on Biological Diversity (CBD).

More recently, other ocean-based CO₂-removal techniques have been suggested, such as the cultivation of seaweed to cover up to 9 per cent of the global ocean. The specific environmental implications of this method have yet to be assessed. Yet such an approach would clearly affect, and potentially displace, existing marine ecosystems that have high economic value, especially in shallow waters.

Back on land, other techniques include those to increase the amount of carbon sequestered in the soil, for example by ploughing in organic material such as straw, reducing ploughing (to limit soil disturbance) or adding biochar. Biochar has an interesting history all of its own, because of the efforts of a band of enthusiastic supporters to persuade the world that this is the answer to global warming. Crop materials or farm wastes are digested by a process called pyrolysis, which produces a liquid and leaves a charcoal-like spongy material that can be dug into soil and allegedly gives it special properties. It is never properly explained how all this disposes of CO_2. Another idea among some enthusiasts is to enhance weathering, which involves the absorption of CO₂ from the atmosphere by certain silicate rocks, especially olivine. The material has to be crushed to provide as much surface area as possible, and thus would need to be spread on beaches and other surfaces as a fine white sand. A slow chemical reaction then ensues which absorbs CO₂ and emits oxygen. It is true, as the enthusiasts, that this is the chemical process in the early Earth which first released oxygen from rocks. Yet to reduce the amount of CO₂ in the atmosphere by 50 parts per million, to get us back to 350 ppm from our current 400 ppm, 1-5 kilograms per square metre of silicate rock would need to be applied each year to 2-6.9 billion hectares of land (15-45 per cent of Earth’s land surface area), mostly in the tropics. The volume of rock mined and processed would exceed the amount of coal currently produced worldwide, with the total costs of implementation estimated to be between $60 trillion and $600 trillion, far more than geoengineering techniques. Like geoengineering, the application would have to be continuous, since once the chemical reaction is over the rock is of no more use and must be covered with fresh layers. Clearly the whole thing is unfeasible. Yet it is crucial to know ore about the permanence of carbon storage for biologically based methods, and the environmental impacts that might result if such approaches are used at vast scale, so a wide range of research is needed.

All these methods therefore have serious, if not fatal, drawbacks. We are left with something that has yet to be invented, but which ought to be the subject of a research programme on the scale of the Manhattan Project, direct air capture (DAC). DAC means pumping air through a system which removes the CO₂ and either liquefies it and stores it or turns it chemically into something else, hopefully something useful. When I say it has ‘yet to be invented’, I mean that a system which is not impossibly expensive has yet to be invented. DAC can, in principle, be undertaken by passing air through anion-exchange resins that contain hydroxide or carbonate groups, which, when dry, absorb CO₂ and release it when moist. The extracted CO₂ can be compressed, stored in liquid form and deposited underground using carbon capture and storage technologies. The huge operational costs for DAC cover a similar range to those estimated for enhanced weathering, at the moment amounting to more than $100 per ton of carbon, although a recent (2016) breakthrough promises $40 per ton. The extraction process would also need land and probably water, and, as for BECCS, there is a risk of CO₂ ­leaking out of geological reservoirs. Such risks can be minimized by storing the liquid CO₂ beneath the sea or by using geochemical transformation, which involves in situ reactions between CO₂ and certain rock types. In theory, cooling (rather than chemistry) to liquefy the CO₂ could also be used to remove CO₂ from ambient air. The technical feasibility, costs and potential environmental impacts of this approach – which could involve setting up plants on high polar plateaus such as Antarctica or Greenland – have yet to be investigated. Since my own belief, based on the above reasoning, is that Direct Air Capture is all that we are left with as a way of maintaining the world in anything like its present condition in the long run, then if we carry out serious research on the scale of the wartime Manhattan Project we may be able to bring down the cost in the same way as solar photovoltaic energy has plummeted in cost in recent years.

A valid criticism of geoengineering or carbon removal is that it encourages us to do little or nothing about reducing our carbon dioxide levels, and that our urgent actions should focus on emissions reduction and not on an unproven ‘emit now, remove later’ strategy. But the unfortunate reality is that the global population, especially in the West, is extraordinarily reluctant to give up the comforts and conveniences of living in a fossil fuel world. We will eventually, because we will have to. But we don’t see why we should just now. Just one more Ryanair flight, and isn’t that SUV a good way of getting the children to school? But even if a drastic and immediate effort is made to cut emissions, significant geoengineering and CO₂ removal operations will need to begin around 2020, with up to 20 gigatons of CO₂ extracted each year by 2100 to keep the global temperature increase below 2^oC. We need to know if that is feasible, in order to answer the next question.”