Geo-engineering/Carbon capture [1]
* Header source: https://www.ft.com/content/88c187b4-5619-11e5-a28b-50226830d644.
The strategy of reducing emissions is problematic and has not worked out as planned. Global emissions have risen instead of decreasing, and it now appears that even cutting annual net emissions worldwide by 2050 may not be enough, because the carbon already emitted stays in the atmosphere for a lengthy period of time. So other alternatives have to be considered.
To limit global warming to 1.5 degrees Celsius, nations will have to remove one trillion tons of carbon dioxide emissions from the planet’s atmosphere this century, and removing the right mix of carbon capture methods will be critical. The methods designed to achieve this are known collectively as "geo-engineering".
The term refers to large-scale interventions in the Earth's climate system designed to halt or reduce global warming, wherein proposals are split into those designed to suck planet-warming carbon dioxide out of the air (carbon capture), and the more radical but also typically faster plans to cool the planet directly by reflecting light, known as solar geo-engineering.
“Man-made ‘volcanoes’ shooting sulphur into the sky. A giant space umbrella made up of tiny mirrored ships to block the sun’s light. Re-freezing the poles by pumping seawater through clouds. Covering deserts in reflective sheeting” are some of the more bizarre methods designed to achieve this.
"Then there's fake metal trees designed to suck out carbon for storage underground. Or barricades to block warm water from building up around the polar ice caps. It's even been suggested the Earth's axis could be pulled a fraction further away from the sun. Many ideas, including "brightening" clouds by pumping seawater into the sky from a fleet of self-steering ships, focus attention on saving the world's two polar ice caps from the big melt. Should the Earth lose their reflective cover, many experts say the climate system will unravel no matter how quickly emissions fall. Others, point to the benefits of white reflective paint on roofs and buildings worldwide".
Methods currently under consideration include:
- Reforestation and afforestation
At the 2020 World Economic Forum, almost every head of State, US President Trump included, threw their support behind a large-scale plan to plant and restore one trillion trees across the globe. Trees are planted to replace clear-cut forests or expand existing ones. They absorb CO2 from the air and convert it into new wood growth, including roots. Trees are still considered among the best carbon capture technology in existence and, unsurprisingly, large-scale land clearing is to blame for a good chunk of emissions. Planting trees is always a good idea but it won't get us out of this. And then there's the problem that trees burn, releasing carbon, even if we don't count that towards our emissions.
- Carbon capture and storage (CCS)
Carbon capture and storage (CCS) describes the process of capturing the carbon dioxide emitted by an industrial process – say, burning gas or coal for electricity or in cement and steel production – and permanently keeping it out of the atmosphere. For large projects, this generally means pumping it underground for permanent storage, typically into the geological formations from which oil and gas have been extracted in the first place: see Figure 11.11 below.
Carbon dioxide capture is arranged either by removing it from the flue gases in a power station, or the fossil fuel feedstock can, in a gasification plant [2], be converted through the use of steam to carbon dioxide and hydrogen as per the graphic below. The carbon dioxide is then relatively easy to remove and the hydrogen used as a versatile battery and fuel. The latter option will become more attractive when the technical and logistic problems of the large-scale use of hydrogen in fuel cells to generate electricity have been overcome.
Various options are possible for the disposal (or sequestration) of the large amounts of
carbon dioxide that result. For instance, the carbon dioxide can be pumped into spent oil or gas wells, into deep saline reservoirs or into unminable coal seams. Other suggestions have also been made such as pumping it into the deep ocean, but these are more speculative and need careful research and assessment before they can be realistically put forward.
In the most favourable circumstances (for instance, when power stations are close to suitable reservoirs and when the extraction cost is relatively small), the cost of removal, although significant, is only a small fraction of the total energy cost.
Because of the rapid increase during the last few years in the number of new coal-fired power stations constructed globally, the need for CCS technology has become more acute. In 2008, the International Energy Agency stated that a substantial number of demonstration plants employing CCS need to be built before 2015 in the USA, Europe, China, Australia and other countries where coal remains a major source of power generation. However, few have been or are being built compared with what is required.
Rapid deployment of CCS to all new coal-fired power stations would enable continuing use of fossil fuels without the deleterious effects of carbon dioxide emissions. Machines that pull CO2 from the air could remove 250 billion tons by 2100. Replanting clear-cut forests could achieve 180 billion tons.
Some advocates also hope CCS will play a role in developing a future Australian hydrogen industry, trapping gas used to make the hydrogen and storing the emissions safely. But its detractors – which include leading engineers and scientists along with climate activists – say that CCS is an unproven and expensive Band-Aid designed to extend the life of unnecessary, dirty industries. They say it is a diversion that has wasted billions of dollars that might have been better spent on reducing emissions.
“You have to ask yourself" postulates Senator James McKim, Acting Greens Leader, "who in their right mind would think it’s cheaper to dig up a fossil, set it on fire, try to capture the emissions and bury it – rather than just whacking up some solar panels?”
in recent years some energy companies have begun piping captured carbon dioxide to oil fields and pumping it into the ground to force more oil to the surface.That process is known as enhanced oil recovery, but is also referred to as carbon capture use and storage, or CCUS. Critics point out that CCUS – the one used to extract oil – is not done to benefit the climate, that it assists in the extraction of a damaging fossil fuel and that the carbon dioxide forced back into the ground is not monitored to ensure it does not leak back into the atmosphere.
There has also been a surge of interest in BECSS, mooted by its most hopeful champions as a solution not only to climate change but to energy shortages. BECSS’ proponents argue capturing emissions from the burning of plants grown for fuel could produce energy that is not simply emissions neutral, but negative. This is because the crop would have absorbed carbon dioxide as it grew, but the capture process would prevent it from returning to the atmosphere when it is burnt.
This involves the use of biomass, in particular the lignocellulosic variety, consisting of a complex of lignin and cellulose present in the cell walls of woody plants such as trees, bamboo, herbaceous grasses and crop residues such as cornstalks. Biomass has become an attractive climate solution because it is, to some degree, renewable. It can be grown again and again.
Let’s take corn as an example. The corn is harvested, then sent to a fermentation vat that converts it to ethanol, which will be trucked to a refinery that will blend it with gasoline for sale. The fermentation process releases carbon dioxide which is captured in a large flue, then sent by pipeline to a wellhead. Pumps send the gas deep below ground, where it will become trapped in sandstone rock.
Biomass in this form is now being given an important role in the blueprints to lessen climate change. In addition to biofuels, it includes biomass burning for electricity and heat, biodigesters that create commercial methane, biochar to improve soil, as well as insulation, building materials and bioplastics. Powerful industries such as electricity, fuel and plastics are betting big on biomass as a feedstock, pushing projected demand sky-high.
But the use of corn for fuel is controversial. Corn could feed people and livestock; growing plants for biofuel takes land that could otherwise be used to grow crops. Burning ethanol in cars produces new CO2 emissions, as does harvesting and trucking the corn. Fermenting, pipelining and injecting all require energy that may come from fossil fuels. It is unclear whether corn-based ethanol can yield even a small net reduction in atmospheric CO2.
The scientific consensus behind the road maps that depend heavily on biomass is that:
- To preserve a climate suitable for civilization, global warming should be limited to 1.5 degrees Celsius above preindustrial levels.
- This requires a 45 percent reduction of emissions by 2030 and zero net emissions by 2050, relative to 2010 levels, according to the IPCC’s 1.5 °C report.
- Humanity’s remaining carbon budget—the amount of future emissions that can be tolerated before surpassing 1.5 °C—is 420 billion to 580 billion metric tons.
- Staying within that limit requires slashing emissions as well as pulling CO2 from the atmosphere. The IPCC estimates that BECCS could sequester 0.4 billion to 11.3 billion tons a year and an average of 1.1 billion to 2.5 billion tons a year from other biomass applications.
The biggest issue is the volume of biomass that would be needed for BECCS. In its 1.5 °C report, the IPCC states that all pathways that limit global warming to 1.5 °C or 2.0 °C require removing carbon dioxide from the atmosphere, on the order of 100 billion to 1,000 billion tons over the 21st century. Removal includes replanting forests, and farming practices can help sequester carbon in soils and perennial plants, but in the IPCC’s scheme, BECCS is cast as the primary tool to stay within the global carbon budget.
Large-scale implementation of bioenergy with carbon capture, alone, would require from 300 million hectares of land—an area roughly equivalent to that of India—to 700 million hectares, the continent of Australia. Converting 300 million to 700 million hectares of cropland to biomass production is simply incompatible with increased food needs. In other words, it is unclear whether corn-based ethanol can yield even a small net reduction in atmospheric CO2. The authors conclude that biomass can play a partial role if greater recycling and more clean cookstoves reduce demand and several agro-forestry techniques increase supply.
And even if BECCS did work, it would need to be deployed across the world in a sudden and massive wave, and it would necessitate felling forests and razing food crops around the world. The European Academies Science Advisory Council recently concluded that negative emission technologies (NETs) have “limited realistic potential” to help mitigate climate change on the scale that many scenarios assume will be needed. Carbon capture and negative emissions technologies also represent a moral hazard, with some governments and industries willing to put off the urgent work of reducing emissions based on the hope of some future technological climate fix.
- Ocean fertilisation
In 2012, controversial US businessman Russ George was accused of breaking two UN conventions when he dumped 100 tonnes of iron filings into the Pacific Ocean off the coast of Canada, the idea being that "fertilising" the ocean with iron would artificially spawn an algal bloom, a kind of carbon sink that would absorb the excess carbon dioxide from the air and draw it down to the bottom of the sea for storage.
Fast-forward to 2029. Imagine that "every merchant ship in the world is fertilising the ocean with iron — a last-ditch effort to draw carbon dioxide from the air as global emissions near the point of no return". Iron filings are sprinkled at sea, helping plankton grow. They breathe in CO2 and convert it into sugar or cellular material. When they die, they sink to the seafloor. Gains would be short-lived, and altering the ecosystem would be risky.
Another alternative is adding lime to 10 per cent of the oceans to enhance alkalinity, increase CO2 uptake and counter seawater acidity.
Crops, mature or organic waste is heated, without oxygen, creating biofuel and biochar – a charcoal-like residue rich in carbon. It is spread onto agricultural fields to improve soil, which can also bind additional carbon.
- Enhanced weathering
Rock is pulverised into dust. When sprinkled on the fields, it draws CO2 from the air and fertilises soil. When spread on the ocean, it reacts with seawater, converting CO2 into carbonates that fall to the sea floor.
- Soil carbon sequestration
Grasses or crops breathe in CO2 and convert it into root material, fixing carbon in the soil. Long-term potential may be limited because soil can only hold so much carbon.
These and a range of other alternatives are the subject of further consideration here and at Solar Radiation Management
Net costs range from $0 (reafforestation) to $300 (direct air capture) per ton. But Conniff (at [1] below) cautions: unless big markets are developed to use the captured CO2, a carbon tax may provide the best support for the techniques.
Other suggestions include:
- Mimicking volcanoes. A modified plane fleet could take off from the tropics, somewhere near the equator, climb 20 kilometres into the sky and during roughly 120,000 flights a year, spray reflective particles directly into the stratosphere, dimming the sunlight hitting the Earth by 1 per cent. “All for just a few billion dollars”.
- Building a giant space shade. Installing some kind of space shade or mirror on high – per medium of a fleet of tiny, reflective satellites moving in unison across hundreds of millions of kilometres in space, could in theory, limit global warming while avoiding both the health and geopolitical consequences of using particles in the lower atmosphere.
Measures under consideration by the Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP), a working group for the UN, include:
- Drawing up cool, nutrient-rich water from the depths with large pipes to create an artificial upwelling that provokes algal blooms while also cooling the ocean's surface
- Injecting liquified CO2 into the seabed in depressions and trenches where it can be stored for 1,000 years.
- Farming seaweed on a large scale before entombing it deep in the ocean to sequester its carbon, or process it for biofuels. If nine per cent of the world's oceans (roughly 4 1/2 times the size of Australia) was converted into seaweed farms for carbon capture, it is calculated that they could draw down to same amount of carbon dioxide that the world emits in a year, roughly 55 gigatonnes.
One obstacle here is the so-called rebound effect: removing CO2 from the atmosphere will see some return from the sea. there is an equilibrium exchange across the ocean surface which governs ocean uptake, depending on the concentration in both the ocean and the atmosphere.[3] If we remove CO2 from either of these reservoirs, the equilibrium will re-adjust. Under this process, the removal of one ton of CO2 from the atmosphere will lead to a reduction less than one ton in the CO2 burden in the atmosphere due to the “rebound” effect where CO2 is released from the ocean.
Also, most current estimates suggest that CO2 removal cannot remove CO2 from the atmosphere as fast as we are putting it in. Thus it cannot be relied upon to counter "business as usual". The most appropriate course would therefore appear to be to steadily reduce CO2 in the years or decades ahead to avoid sea level rise to dangerous levels.[4]
[1] With the exception of the segment on CCS (which is an edited summary of portion of Chapter 11 of Sir John Houghton's book, Global warming - the Complete Briefing, 5th edn, 2005, Cambridge UP, pp 212-213) and BECCS, the remainder is an edited summary of the article "The last resort" by science-writer Richard Conniff published in the January 2019 edition of Scientific American, pp 50-57. On this topic generally, see the article "Can removing carbon dioxide from the air save us from climate catastrophe?" at https://blogs.ei.columbia.edu/2018/11/27/carbon-dioxide-removal-climate-change/ and the article "We must remove carbon from the atmosphere to limit climate change: here's how we can do it", at https://www.newsweek.com/we-must-remove-carbon-atmosphere-limit-climate-change-1206971; also the National Academies Press production: Climate Intervention: Carbon Dioxide removal and sequestration and reliable Sequestration at https://www.nap.edu/read/18805/chapter/3
and the chapters which flow in sequence.
[1.5] This is an edited summary of the article "The biomass bottleneck" by Eric Toensmeier and Dennis Garrity which appeared in the Ausgust 2020 edition of Scientific American, pp 60-67.
[2] Gasification: the process of producing syngas –a mixture consisting primarily of carbon monoxide (CO), hydrogen (H2), carbon monoxide CO2), natural gas (CH4), and water vapour (H2O)–from coal and water, air and/or oxygen: https://en.wikipedia.org/wiki/Coal_gasification
[3] Associate Professor Michael Box (UNSW, retired), Geoengineering: Messing with the Climate to Combat our Current Mess, WEA course, 16 August 2019 at [3.2]
[4] Ibid, [3.4]. See also the final comment on Solar Radiation Management
Next