You might suppose the term “negative emissions” refers to bad things. But when it comes to climate change, it’s the emissions themselves (mostly CO2) that are bad, whereas reducing them is good. So negative emissions are a positive benefit.
Carbon dioxide is not inherently bad; it’s part of nature. We exhale it all the time and plants inhale it. However, nowadays there are more people, cows, tailpipes, smokestacks, and fracking wells emitting carbon gases, but fewer trees taking it in. That’s the problem. Human activities are now emitting about 28 billion tonnes of CO2 per year, thereby increasing the earth’s temperature, and bringing hurricanes, forest fires, desertification, floods, ocean acidification, and disease epidemics.
In Paris three years ago, we agreed to limit the temperature rise to 2 degrees C, so as to limit most of these problems. But in October 2018, the IPCC warned us to keep our emissions even lower, so as to limit global warming to 1.5 degrees.
It is already too late to achieve that goal; we will even “overshoot” the 2 degree limit, but with enormous effort it’s possible then to pull back down below 1.5 degrees.
How so? We cannot merely reduce our carbon gas emissions to zero, but must also urgently increase our negative emissions. That is, having poured CO2 into the air for centuries, now we must stop doing so and, by the century’s end, be sucking back about 20 billion tons of it each year, locking it away in “sinks.”
That’s a stupendous amount and researchers are only beginning to develop the necessary “Negative Emissions Technologies” (NET). Below I will list alphabetically five NETs that can help reverse the flow.
Unlike the more problematic “geo-engineering” technologies, which counteract symptoms of climate change by adding other potentially risky things to the environment, NETs undo the basic problem itself: the excessive proportion of carbon gases in the atmosphere.
Plants grow by using CO2 in photosynthesis. Trees retain huge amounts of carbon until they die and burn or decay, releasing it back into the air. Planting trees is the most promising NET of all. We need to add a trillion trees to the earth’s forests, especially in tropical areas, where their effects on the climate are strongest.
Some efforts are already underway. Several countries are planting a “great green wall” of trees straight across Africa to block the southward spread of the Sahara. And the Tamils of southern India are assigning each person two or three saplings to plant and water per year in reviving their depleted land.
Perhaps best of all, some new companies are planting with drones. One firm can plant 38,000 trees per day. Each drone flies about a meter above the soil and shoots into the soil a pellet containing a seed and a nutrient gel, which breaks open. The drone then sprays water and moves on. The method is not as effective as planting by hand, but it costs little and is being used to reforest clear-cut land. The drones can also plant on rocky hills where people cannot go.
But forestry often competes with agriculture for the use of land. Some such conflicts could be resolved by growing crops such as coffee in the shade of fruit trees.1 Other disputes, however, will require hard political decisions.
Rich soil is heavy with carbon, microbes, and other living matter. Today, however, much of the world’s soil is dead, producing less nutritious food and requiring fertilizers that pollute lakes, rivers, and even the ocean. The challenge is to regenerate the soil by adding carbon to it with smart farming, and retaining it there.2 Since ploughing exposes the soil to the air, releasing the carbon, one solution involves “no-till farming”—injecting seeds directly into the ground without ploughing it.3
Another answer is to apply charcoal (called “biochar”) to the soil. Organic waste products (e.g. scrap lumber, turkey feathers, old cardboard boxes, and sewage) are pyrolized (burned without oxygen) to make biochar, which can retain the carbon in soil for thousands of years, reviving it and increasing crop yields markedly.4
Biomass is organic material, primarily found in the form of living or recently living plants and biological wastes containing carbon. During ordinary industrial processes, it is burned and/or released in other ways to the atmosphere as CO2 . This must stop. Instead, IPCC insists that renewable biomass waste must be used to produce biofuels such as biogas and bioethanol. The CO2 resulting from burning these fuels then must be captured and sequestered in geological formations, where it can stay in place for more than 1,000 years.5 Biomass used in that way constitutes a form of NET, reducing the absolute amount of CO2 in the atmosphere.
BECCS will require large areas of land—an estimated 300 million hectares to remove 10 billion tons of CO2.6 That’s the size of India!
Moreover, we must make sure that the biomass is not grown on land that should instead be used for food production.
Remarkable NET advances have recently occurred in the technology of capturing carbon directly from ambient air. There is nothing new about the idea; scientists have long been able, with water and energy, to remove CO2 from the air, but the process has been prohibitively costly.
However, within the last few years pilot plants have been built that can produce purified, compressed CO2 at a price of $100 to $150 US per tonne.
In Squamish, B.C. David Keith’s company, Carbon Engineering, is producing CO2 and turning it into low-carbon intensity fuel.7 They could be burying it instead, which would make their plant a source of negative emissions, but for the sake of financing the pilot operation, their current production is approximately emissions-neutral. The company is seeking investors to build a full-scale commercial facility.
In Zurich, Switzerland a commercial firm called Climeworks8 is capturing CO2 in partnership with Audi, whose cars will use the product, a renewable fuel. A greenhouse company also purchases its CO2 for growing vegetables.
Climeworks uses heat from the town’s incinerator, and their plant in Iceland uses geothermic energy. It now costs the company $600 to produce a tonne of CO2. Their long term target price is $100 a tonne, but they recognize the need for more research to make this possible. Although their goal is to capture one percent of global emissions by 2025, they admit that this cannot be done by commercial investment only; a vast increase in global political will is essential.9
Stephen Pacala, who chaired a panel for the US National Academies of Science, expects DAC to be in widespread use within the next decade.10 Normally, however, decades of preparatory work precedes the introduction of such a new technology. In any case, a physicist friend has calculated the cost. She notes that at $100 per tonne it would cost $2.8 trillion annually to remove all the CO2 human beings emit. No one is proposing such a huge project; we will of course have to reduce our emissions and use several other NETs. Still, her point is valid; we must not let the DAC option give us false hopes for a painless transition.
On the other hand, we shouldn’t overlook the opportunities either. Because the atmosphere circulates constantly, the CO2 is quite evenly distributed around the globe, so it hardly matters where the removing takes place. A billionaire philanthropist could begin this year building plants designed by David Keith or Climeworks on a desert island over a saline aquifer, to remove billions of tonnes of CO2 and sequester it permanently. If you know any billionaires, please drop the hint that it would be a nice thing to do.
Mother Nature has her own way of subduing carbon dioxide: “mineral weathering.” As rain is falling it collects CO2, then hits minerals on the ground, combining with them for form carbonates, alkaline compounds that flow in streams to the ocean. There it counteracts the ocean’s acidification and ultimately sinks to the seabed where it remains for thousands of years. Today this natural rock weathering absorbs about 0.3% of global fossil fuel emissions.
The earth’s surface contains abundant minerals that weather in the same way whenever exposed to air. Some scientists propose to dig them up, crush them to a powder, and spread it on the soil, where it will incidentally improve agricultural fertility. This NET, called “enhanced weathering,” would sequester very large amounts of carbon, as claimed, but it is too costly to be feasible on the scale required.11
However, the idea has some limited utility. Mining always leaves huge piles of tailings near the mines. Some tailings are composed of the minerals required for enhanced weathering. The surface of each pile hardens with exposure to air, but the stuff underneath can indeed be scattered on farmland, where it will bind a little of the excess carbon dioxide and remove it from our atmosphere Let’s use what’s readily available.
Metta Spencer is editor of Peace.
1 Patricia Moguel, Victor M. Toledo (1999). “Biodiversity Conservation in Traditional Coffee Systems of Mexico”. Conservation Biology. 13 (1): 11-21.
2 A. N. (Thanos) Papanicolaou, Kenneth M. Wacha, Benjamin K. Abban, Christopher G. Wilson, Jerry L. Hatfield, Charles O. Stanier, Timothy R. Filley (2015). “Conservation Farming Shown to Protect Carbon in Soil”. Journal of Geophysical Research: Biogeosciences. 120 (11).
3 Baker et al. (2007) Tillage and soil carbon sequestration—What do we really know?. Journal of Agriculture, Ecosystems & Environment. Volume 118, Issues 1 #42375-2401.
4 Dominic Woolf, James E. Amonette, F. Alayne Street-Perrott, Johannes Lehmann, Stephen Joseph (August 2010). “Sustainable biochar to mitigate global climate change”. Nature Communications. 1(5): 1-9.
5 IPCC, (2005) “Chapter 5: Underground geological storage” IPCC Special Report on Carbon Dioxide Capture and Storage. Prepared by Working Group III of the Intergovernmental Panel on Climate Change [B. Metz, O. Davidson, H. C. De Coninck, M. Loos, and L. A. Meyer (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp195-276.
6 “Extracting carbon from nature can aid climate but will be costly: U.N.“ Reuters. 2017-03-26.
7 Carbon Engineering’s website is carbonengineering.com/about-dac
8 Climeworks’ website is www.climeworks.com
10 Elizabeth Kolbert, “Climate Solutions: Is it Feasible to Remove Enough CO2 from the Air?” YaelEnvironment360. www.carbonbrief.org/swiss-company-hoping-capture-1-global-CO2-emissions-2025
11 David Beerling, “How ‘enhanced weathering’ Could Slow Climate Change and Boost Crop Yields.” CarbonBrief, Feb, 19, 2018. www.carbonbrief.org/guest-post-how-enhanced-weathering-could-slow-climate-change-and-boost-crop-yields