If we care about our earth (and the readers here are most likely to) the story is quite simple: We emit 40 billion tons of carbon annually, and little is being done to reduce it. There is also not much likelihood of any action from our leaders, given the Senate vote on the Green New Deal and President Trump’s well-known views on the subject. So how do we get rid of the carbon about to turn earth into a living hell? Deadlines have been clearly laid down by experts.
The October 2018 IPCC report on limiting global warming to 1.5C above preindustrial levels notes human-caused CO2 emissions would have to achieve ‘net-zero’ by 2050. According to the report, this would necessitate ‘far-reaching transitions’ not just in how energy is used and produced but also in the use of Negative Emissions Technologies (NETs) such as carbon recapture from the air. We have to stabilize earth or eventually a self-reinforcing feedback loop will lead to uncontrollable warming and a “Hothouse Earth” without any means of reducing earth temperatures.
Scientists assessing NETs find that restricting global warming to 1.5C requires large-scale deployment of NETs; in fact, a major national effort. Moreover, any single NET is unlikely to be sustainably adequate, rather multiple NETs each on a more modest scale is the most effective scenario. A comprehensive analysis is therefore both illustrative and illuminating.
Direct air carbon capture and storage (DACCS) is an enticing prospect until one examines the costs. Scientific scenarios project DACCS capacity to remove 10-15 billion tons of CO2 per year by century’s end. Optimists up it to 35-40 billion tons solving the CO2 problem in one fell swoop. Not so, say those who have examined costs.
A group from the Mercatur Research Institute on Global Commons and Climate Change and Humboldt University of Berlin and in particular Sabine Fuss have examined costs reporting on different NETs in Environmental Research Letters (ERL, June 2018). They put the cost at $100-300 per ton for DACCS and estimate sustainable removal at 0.5 – 5.0 GtCO2 per year — a Gt is approximately a billion tons. The upper level would still cost $500 billion to $1.5 billion according to them.
The other major problem with DACCS is the sheer energy required. Removing a million tons a year would consume 300-500 MW according to Jennifer Wilcox of Worcester Polytechnic. The power needs to be clean energy for a coal-fired plant would generate more CO2 than would be extracted.
Climeworks is a company based in Switzerland that has developed a DACCS process. Its pilot plant in Hellisheidi, Iceland, is using geothermal energy to remove CO2 from the air and store it in basalt. They have also announced a commercial scale venture in Zurich, Switzerland.
In addition to active air capture as described, there is a passive approach. An Arizona State University professor has developed a resin that when dry absorbs CO2 from the air, relinquishing it when immersed in water. The team envisions artificial trees made from the resin each capable of capturing a daily ton of CO2.
Afforestation, namely adding to forests, and reforestation are intuitively attractive. But there are limitations because of competition for land from food production. The CO2 removal is estimated at 0.5-3.6 billion tonnes of CO2 (GtCO2) per year (ERL, June 2018). Of course given demand for land its use is reversible, and over time cost is likely to increase.
As an addendum to afforestation one might note an investment by Apple on a project by Conservation International to restore and protect 27,000 acres of mangroves in Columbia. This will capture a million tons of CO2 annually as ‘blue’ carbon stored in coastal marshlands and mangroves can be up to ten times more dense than in forests.
Bioenergy carbon capture and storage (BECCS) is also being employed. As an example, Archer Daniels Midland began to capture CO2 emitted at its Decatur, Illinois, ethanol plant in 2017. It is now successfully storing a million tons of CO2 per year underground Scientists estimate the potential of BECCS at 0.5-5.0 GtCO2 per year (ERL, June 2018). The technology is stable with good future prospects when other manufacturers also try to (or are obliged to) achieve carbon neutrality.
Biochar is formed from the pyrolysis of agricultural and forestry waste in a controlled process with reduced oxygen. Not only is the carbon prevented from escaping but the char can be used to improve soil quality. It can prevent from 0.5-2.0 GtCO2 per year from polluting the atmosphere, and scaling will reduce costs enhancing its potential.
Enhanced weathering refers to the improved absorption of CO2 by rocks like basalt to levels higher than the natural slow process. The Potsdam Institute for Climate Impact Research estimates the cost at $200 per ton of CO2 using basalt and $60 per ton for dunite i.e. about double the cost for afforestation. A handicap perhaps but afforestation is limited by land availability, and absorption by basalt could remove up to 4.9 GtCO2 annually, according to Potsdam estimates. For best results, the rock has to be mined, ground up and spread out since CO2 absorption levels are heavily dependent on grain size. The process does appropriate land limiting use in arable areas.
Soil carbon sequestration can absorb up to 5 GtCO2 per year (2018). It requires providing a continuous cover instead of letting fields remain bare after harvest to reduce carbon loss. Other methods include no-till or conservation tillage. The accumulated benefits with cropland, however, can be temporary and easily eroded if the land is ever plowed, calling for education programs in addition. There is also agroforestry i.e. combining farming with trees and livestock grazing, which can be an option in some, but not all, farms and climates.
A new attractive technology is the direct conversion of CO2 into fuel. It is an approach being used by Carbon Engineering of Squamish, B.C. in Canada. Air-captured CO2 and supplemental hydrogen split from water are combined to produce gasoline and diesel for less than $4 per gallon. The hydrogen removal uses renewable energy.
Of the 40 billion tons of CO2 emitted annually, half is absorbed naturally. The 20 billion tons remaining at present require human input to be eliminated. A strategy employing a variety of techniques makes particularly good sense given the unusual possibilities opening up and the limitations of any single method. On the other end of the scale, radical transitions in energy usage, transport, buildings, even cities, coupled with low-emissions energy production will reduce annual emissions. What is left has to be recaptured to attain net carbon neutrality. It is a monumental task requiring international cooperation including, if necessary, monetary incentives for poor and middle income countries. Of utmost importance is to get started.
It is an insidious ailment for planet earth, its presence felt by the extraordinary intensity of extreme weather events — Cyclone Eline and Idai devastating Mozambique in quick succession, for example, were an unexpected event for the southern hemisphere. On the other hand, such vagaries of weather as a cold spell, can draw mockery from President Donald Trump who proposes to do nothing. He has emboldened others like Jair Bolsonaro, the new President of Brazil.
The real question is whether the American people will exercise profound discernment when the next election comes around. If the senate’s confidence is any judge, they will not. The senate voted 57-0 against the Green New Deal, the number including two Democratic senators. The remaining Democrats voted ‘present’. Not one Democrat stood up to be counted for GND under the pretense the Republicans were trying to split them.
Carbon capture has potential but who is going to invest in the processes to realize it? Certainly not current senators who just voted for the opposite. At the very least if they passed a law requiring net-zero emissions by 2050, it would encourage private enterprise to self-clean or provide services for others to do so. But what are the chances of any of this happening? Almost none without pressure would not be a bad guess. Perhaps Greta Thunberg and her young cohorts are showing the older generations the way.