Massive Plantations: A Viable Means of Carbon Sequestration?
A recent article in Wired offered a cogent critique of the foremost technofix put on the table as a solution for the climate crisis 1. The article, “The Dirty Secret of the World’s Plan to Avert Climate Disaster,” by Abby Rabinowitz and Amanda Simson, reveals that the key technology at the heart of half of the IPCC’s models to hold global warming to 2°C, known as “bioenergy with carbon capture and storage” (BECCS), would burn cultivated crops for electricity, and then capture and store the resulting carbon dioxide underground. BECCS is a largely untested computer model. But, the IPCC models rely on it scrubbing some 630 gigatons of CO2, “roughly two-thirds of the carbon dioxide humans have emitted between preindustrial times and 2011,” from the atmosphere at a cost climate scientist James Hansen estimated at $140–570 trillion this century.2 If implemented, according to climate scientist Kevin Anderson, BECCS would require a land area the size of up to two Indias and a water supply equivalent to the entire current global agricultural usage, among other major difficulties.3
Another piece, in the April 17, 2017 edition of Frontiers of Marine Science, by Carlos Duarte, et al., “Can Seaweed Farming Play a Role in Climate Change Mitigation and Adaptation?” offered something of a variant on BECCS, based on the significant carbon uptake and storage capacity of seaweed. They proposed the massive expansion of kelp farms to supply biomass for energy or food production, as a “Blue Carbon” strategy.4 The economic side of these various schemes, even should they prove viable, would require funding and implementation on an enormous scale.
The kelp-farming article referenced various ecological problems: “the expansion of seaweed aquaculture need also consider potential impacts, such as the introduction of invasive species.” The authors concluded that current aquacultural experience indicates that this problem “is not severe.” This assertion was contested by a number of researchers.5,6 For example, Buschmann, et al. (2014) wrote,
…awareness is developing regarding the environmental side effects, which may occur as a consequence of large-scale farming, occupying extensive marine areas. By altering the habitat and the involuntary spread of cultivars of algae to adjacent areas, seaweed farming appears to affect many components of natural communities, e.g. bacteria, meiofauna, benthic macrofauna, fish and corals. The installation of large beds of seaweed can contribute to complex modifications of local species interactions, which are not yet well understood.
The same authors exemplify their concern:
For example, Eucheuma denticulatum and Kappaphycus alvarezii have been farmed in shallow lagoons […]. In the mid-1990s, farms covered a total area of approximately 1000 ha. If left unmanaged, such a development could, in the worst case, contribute to large-scale ecosystem changes (e.g. extensive seagrass loss, or spread of farmed algae to adjacent coral reefs), with implications for the production of several ecological goods and services.
This is apparently exactly what occurred in Hawaii, according to a 2001 Science article by Naylor, et al. They reported that “no restrictions existed to prevent the escape of seaweed species introduced in 1973 to Hawaii; they have since spread rapidly across the state’s coral reefs.”
Even barring escapes, the Buschmann paper alluded to more general and pervasive problems. In fact, these are relevant to any large-scale, factory-type mono-cultivation. Such activities must inevitably attenuate or destroy ecosystem functions and services. And keep in mind that the sorts of agri- or aquaculture envisioned for carbon dioxide reduction would be conducted at enormous scales.
“Biodiversity and Ecosystem Functions (BEFS)” and Carbon Sequestration
The term, “ecosystem function” refers to those processes associated with maintenance and growth of ecosystems, such as carbon and other nutrient cycling, net and gross productivity, resilience and resistance to invasive species, parasites and pathogens. The term “ecosystem services” further refers to those functions that respond to human needs or usage. Those with an anticapitalist bent tend to look askance at this concept, through which many ecologists seek to monetarize such functions. Nevertheless, it includes things like water supply, nitrogen cycling, carbon fixation, soil formation and aesthetic values, which are important in any case.
For over two decades now, the ecological field of “biodiversity and ecosystem functions and services” (BEFS) has researched, documented and reached broad consensus on the positive association between biodiversity (ranging from landscape to species to functional and to genetic diversity) and ecosystem functions and services. For example, among recent works, a 2014 study in Limnology and Oceanography by Olli, et al., observed increasing marine phytoplankton biomass in the Baltic Sea “at the ecosystem scale” due to “long-term positive biodiversity change, which contrasts with the trend of global biodiversity loss.”7 A study on soil biodiversity, published in the Proceedings of the National Academy of Sciences by Wagg, et al. (2013) noted that “this vast and hidden diversity contributes to the total terrestrial biomass and is intimately linked to above-ground biodiversity.”8 And a review study by van der Sand (2017) in Current Opinion in Environmental Sustainability drew on empirical, remote sensing and ecosystem modeling in tropical forests indicating that “biodiversity significantly and positively affected carbon storage and/or sequestration in the majority of the empirical studies (75%) and remote sensing studies (90%) and a positive effect on long-term carbon in the most recent models.”9 Thus, in general, biologically diverse ecosystems show significantly higher rates of carbon sequestration in soil and biomass than stands of one or two species of plant, such as is the norm in large-scale agriculture.10,11 Multiple mechanisms underlie this relationship, including the redundancy and complementarity of functions and organisms in biologically diverse ecosystems. In turn, these functions determine whether an ecosystem is a source or sink for CO2 and other greenhouse gases.
Capitalist, large-scale, monocrop cultivation—whether in agriculture, silviculture, aquaculture, animal husbandry or in suburban lawns and golf courses—represents an existential threat to biodiversity. At the community level, it displaces existing biota, impacting both above-ground and soil communities. It replaces those communities with depleted, ecologically dysfunctional systems. And repercussions extend to other ecosystems through associated measures such as fertilizer run-off, pesticide spraying or predator control.
Monocrop cultivars are susceptible to parasites and pathogens. In complex ecosystems, diverse species and genomes, and patchy habitats limit the spread of the latter, a basis for the “resilience” and “resistance” of ecosystems. Agroecologists have documented and relied on these associations for decades (Altieri, 1999).12 Pathogen and parasite resistance is reduced in depauperate, homogeneous systems, to be replaced by use of various pesticides or anti-microbials, all of which are produced and deployed using large amounts of fossil fuels.
Nutrient cycling and soil structure is also reduced over time in factory farming systems. To sustain high yields, agriculturalists must rely on ever-increasing amounts of exogenous fertilizers, either synthetic or manure, shipped in to replace nutrients lost to distant markets, and whose addition further degrades the soil, which was noted in the late 19th century by Karl Marx in Das Kapital, following the chemist Justus von Leibig. Water is also consumed in ever-increasing amounts, due to loss of the soil’s water retention capacity and excessive demand of many cash crops, cultivated based on profit, not climate or soil vocation, and selectively bred to maximize returns, rather than for adaptation to local conditions. Additional mechanical and chemical inputs are required to protect and harvest crops or care for extensive lawns or greens. All such inputs bear large and increasing carbon footprints, with fertilizer production remaining a major source of greenhouse gases.
Ecosystems and Carbon Sequestration
By far the greatest carbon sink is the ocean. Oceanic carbon is mostly sequestered and stored through the bicarbonate buffer system in the water column, or as carbonates in the sediment, rather than as living or dead biomass. In terrestrial ecosystems, however, whether a terrestrial ecosystem is a source or a sink depends to a large degree on three major ecosystem functions: net primary productivity (NPP),a total biomassb (and its allocation) and soil respiration, a function of soil organic carbonc (SOC or SOM).13 Of course, these functions also depend on climate, geology, soil type, and—in agriculture—the types of crops and cropping. Of terrestrial ecosystems, tropical forests represent the largest single pool of stored carbon, and, together with tropical grasslands, the greatest mass of total net primary production, but they do not boast the highest average NPP, nor of carbon storage: wetlands, and especially mangrove ecosystems (called “mangals”) do. In fact, mangals are “among the most carbon-rich forests in the tropics”14 and “are considered a significant carbon sink”15 Mangals, and other wetlands, together with grasslands store most of their carbon as SOC. Tropical rainforests, on the other hand, and to a lesser degree temperate and boreal forests, store most of their carbon in the form of above-ground biomass. The form of storage has important implications for greenhouse gas emissions during land conversion and cultivation. When tropical rainforests are cleared, for example, the bulk of the carbon is quickly released into the atmosphere and the remaining soil is depleted of organic material. In turn, cultivated lands, generally speaking, fall within the lower range of carbon sequestration and storage.16 The following table, collated from various sources, will give some rough idea of NPP and carbon storage in various terrestrial ecosystems and cropland.
|Summary of C stocks in terrestrial Ecosystems 17|
|Biome/Ecosystem||Area (109 ha)||Global carbon stocks (Mgd C)||NPP (Mg C per year)|
|Plants||Soil||Total||Total * 109||Avg (ha-1)|
|Total *109||Avg (ha-1)||Total * 109||Avg (ha-1)||Total * 109||Avg (ha-1)|
|Tropical savannas and grasslands||2.25||66||29.3||264||117.3||330||146.7||17.7||7.9|
|Temperate grasslands and shrublands||1.25||9||7.2||295||236||304||243.2||5.3||4.24|
|Deserts and semi-deserts||4.55||8||1.8||191||42.0||199||43.7||1.4||0.3|
Ecosystem loss and biodiversity decline combine with SOM disturbance to reduce the terrestrial biosphere’s carbon capture ability and increase greenhouse gas emissions. A recent, dramatic example was provided by a recent study using 12 years of MODIS satellite data,21 cited in a Guardian article last fall: “the world’s tropical forests are so degraded they have become a source rather than a sink for carbon emissions.”22
The Guardian piece elaborated further:
Researchers found that forest areas in South America, Africa and Asia—which have until recently played a key role in absorbing greenhouse gases—are now releasing 425 teragrams [1 teragram (Tg) = 1 billion kg] of carbon annually, which is more than all the traffic in the United States.23
Global agriculture has long been a major source of atmospheric carbon 24,25, although it was overtaken by fossil fuels over the past century and a half. Estimates that global agriculture is responsible for 20% of greenhouse gases, with an additional 14% contributed by deforestation and other land-use changes.26
Soil organic material is processed by unseen ecosystems, the soil biota and especially microbiota. Soil and sediment microbes mediate the carbon and nitrogen cycles.27 Thus, anthropogenic changes or disruptions to this microbiodiversity can also interrupt carbon or nitrogen storage, releasing significant amounts of greenhouse gases. Such disruption occurs during land conversion and ongoing cultivation in which both mechanical processes and chemical inputs disrupt soil microbiota.
It is well documented that land conversion is second only to fossil fuel combustion as a net source of atmospheric greenhouse gases. From 1960-2016, land use changes were estimated to have pumped up to 1.4 Gigatons of carbon per year into the atmosphere.28 A meta-analysis of studies of tropical land-use changes noted that the highest carbon losses were observed in conversions of primary forest to agricultural uses.29 Agronomist Fred Magdoff noted that,
The worst [case] I know of (that is the most rapid CO2 emissions) occur when organic soils in Indonesia are drained, burned, and converted to oil palm plantations. It will take over 400 yrs. to “pay back” the extra atmospheric C with biodiesel.30
Janzen (2014) discussed the reasons for the massive release of carbon as a result of land conversion for agricultural use in western Canada:
This conversion had at least two effects on stored C (…). First, it stimulated the rate of decomposition, because the physical disturbance exposed previously protected organic matter to biological activity and also increased soil water by periodically suppressing plant growth. Second—and this may be the more important (and sometimes overlooked) effect—farming sent away large proportions of the C acquired by photosynthesis. That, after all, is the point of farming—to capture, by photosynthesis, C in some marketable form and export it for profit.31
Various conventional agricultural practices, such as tillage, removal of plant debris, leaving land fallow, and use of chemical inputs can degrade soil structure, lead to erosion and alter or destroy soil microbiota, resulting in significant emissions of greenhouse gases.32 For example, a long-term field study of effects of tillage and fertilization in Germany found the highest carbon and nitrogen storage in fields with reduced tillage, and the highest greenhouse gas emissions in conventionally tilled fields 33. Liu, et al. (2014) provides estimates of carbon balance for various ecosystems in the eastern half of the U.S. for the period 2001-5. Agriculture added to the atmosphere a net 53 tons of CO2 equivalents (comprising various greenhouse gases) per square kilometer per year. The same author showed that forest and grassland ecosystems are carbon sinks. Forests sequestered 586 tons, and shrub/grasslands stored another 126 tons per year in this region. The figures vary by region and type of agriculture practiced. For example, in the Ozark, Ouichita-Appalachian forests, agriculture sequestered 10 tons of greenhouse gases per km2 per year, while forests absorbed 626 tons. In the U.S.’ historic breadbasket, the central plains, agriculture emitted 124 tons per year, while forests sequestered 440 tons.34
Houghton (1999) provides figures for the relative carbon content in biomass and soil in various ecosystems in undisturbed and cultivated states, and estimated time for recovery of soil and biomass, which also illustrate the consequences of ecosystem loss and land conversion, as well as the relative degrees of carbon storage in undisturbed vs. cultivated systems. For example, the vegetation in an undisturbed North American deciduous forest holds 135 Megagrams of carbon per hectare, while the soil holds 134 MgC/ha. When converted to conventional cropland, plants and soil hold 5 and 101 MgC/ha. It would take an estimated 50 years without disturbance for plants and soil to recover naturally. Carbon in Latin American tropical rainforest declines from 200 to 5 MgC/ha in plants and from 98 to 74 MgC/ha in soil, and would require 40 years for recovery.35
Global agriculture seems to fluctuate between being a slight carbon source and a slight carbon sink (slight being teragrams of carbon per year) over decades.36 Yet, perhaps unsurprisingly, there is indirect evidence that extensive monocrop cultivation of cash crops may well be a net carbon source, and, in any case, is far more carbon intensive than other forms of cultivation. For example, in the U.S., major cash crops have higher rates of carbon emissions than other cultivars. Rice cultivation is highly capital intensive and grown on large monocrop plantations. For the year 2004, as an indicator of capital (and fossil fuel) intensity, 78% of rice cultivation by area employed conventional tillage and incurred the highest energy usage. Rice cultivation, as a whole, released approximately 1008 kg of total carbon per hectare into the atmosphere. Cotton, another capital and input-intensive crop, was second in tillage and energy usage, and emitted the second highest amount of carbon, 882 kg/ha. These are followed in all categories by corn, hay and successively, other major grains.37
When I began researching and writing this piece, I simply wanted to critique geoengineering schemes that purported to ameliorate the climate crisis through by way of massive cultivation of food or biofuel crops from the perspective of the subfield of ecology known as Biodiversity and Ecosystem Functions, within a “metabolic rift” framework. But, after speaking with Marxist writer and soil scientist Fred Magdoff, I realized this was insufficient. What was required was a somewhat broader, ecosystem framework, which is even farther afield from my area of phylogeography and population genetics. Which means that this essay is, of necessity, suggestive and probably wrong in some particulars. What I hoped to propose was that these geoengineering approaches represent capitalist (Cartesian) technofixes that would not only fail to resolve the accumulation of greenhouse gases, but would engender complicating crises down the road. In particular, there is considerable evidence of the following:
- Biodiversity decline leads to ecosystem degradation and loss of functions and services, particularly those associated with greenhouse gas sequestration and storage.
- Diverse ecosystems usually, but not always, demonstrate higher rates of carbon sequestration and storage than stands of single species or depauperate ecosystems.
- Even when mono-species stands show high rates of carbon sequestration, they lack the multifunctionality of diverse ecosystems, which means that they lack resistance and resilience in the face of environmental variability, pests and pathogens.
- Whether directly related to the foregoing, or not, major natural, undisturbed ecosystems show higher primary productivity and store more carbon in both biomass and soil than most agricultural systems. And their greater intrinsic resilience and resistance means that they don’t require massive fossil-fuel expenditures on pesticides, irrigation, fertilizers and other inputs. And this doesn’t even mention livestock.
- What is more, the destruction of those ecosystems and their replacement with agricultural systems, property development, etc., has historically been the major source of atmospheric greenhouse gases, only superseded by fossil fuel combustion during the past century and a half. And the most productive ecosystems—largely in the global south—are the ones disappearing at the most prodigious rates.
My argument would have benefitted from hard data regarding respective contributions to greenhouse gases by agricultural sector. While global data indicates that agriculture (as opposed to land conversion) is varies, over decades, from being a slight carbon sink to a slight source, there is some evidence that suggests that capitalist, large-scale, monocrop agriculture is a net greenhouse gas producer—a carbon source. I suggested some reasons for this from both BES and Ecosystem points of view. But, it might be useful if someone did some multivariate statistics looking at things like type of cultivation system (monocrop, agroforestry, etc.), farm area or capital investment, type of tillage, crop rotation, etc., and greenhouse gas emissions, while controlling for factors like climate or soil types. It would also be useful to have data comparing carbon fluxes in agroecological systems with conventional agriculture. And it would be useful to detail the social and technical characteristics of agriculture in each of the ecoregions discussed by Liu and associates (2014) in their paper on carbon fluxes, cited above.
I also make the assumption that proposed geoengineering schemes would follow the pattern of most capitalist agricultural production schemes. Voices from within the climate change establishment seem to verify that these are envisioned as giant, market-driven monocrop plantations. Designers unquestionably assume an appeal to private investors, who would seek to realize a profit. According to the not-for-profit Center for Carbon Removal:
No commercial BECCS electricity plants exist (though a biofuels + CCS plant is currently operational in IL), but encouraging signs out of the UK on fossil CCS developments give hope that BECCS power isn’t too far away from commercial reality.38
All of which suggests that the most viable form of carbon sequestration, squared with human needs, would be to engage in massive ecosystem restoration combined with various agroecological forms of production. But, if we consider that fossil fuels contribute eight times as much atmospheric carbon as land conversion, the second major source, our principal focus must remain on reduction and elimination of fossil fuel use.
- ↩NPP is the net assimilation of CO2 in an ecosystem, mostly by photosynthetic organisms, after factoring out respiration.
- ↩Total biomass includes both living and dead material (mostly plants), usually expressed as dry weight.
- ↩SOC consists of decomposed animal and (mostly) plant material forming the organic (humus) component of soil.
- ↩1 Megagram (Mg) = 1 thousand kg.
- ↩Abby Rabinowitz and Amanda Simson, “The Dirty Secretof the World’s Plan to Avert Climate Disaster,” Wired, December 10, 2017.
- ↩Rabinowitz and Simpson, “The Dirty Secret.”
- ↩Rabinowitz and Simpson, “The Dirty Secret.”
- ↩The Blue Carbon Initiative(website).
- ↩Buschmann, A. H., Prescott, S., Potin, P., Faugeron, S., Vasquez, J. A., Camus, C., … & Varela, D. A. (2014). “The status of kelp exploitation and marine agronomy, with emphasis on Macrocystis pyrifera, in Chile,” Advances in Botanical Research(Vol. 71, pp. 161-188).
- ↩Naylor, R. L., Williams, S. L., & Strong, D. R. (2001). “Aquaculture-a Gateway for Exotic Species,” Science, 294(5547), 1655-1656.
- ↩Olli, K., Ptacnik, R., Andersen, T., Trikk, O., Klais, R., Lehtinen, S., & Tamminen, T. (2014). “Against the tide: Recent diversity increase enhances resource use in a coastal ecosystem,”Limnology and Oceanography, 59(1), 267-274.
- ↩Wagg, C., Bender, S. F., Widmer, F., & van der Heijden, M. G. (2014). “Soil biodiversity and soil community composition determine ecosystem multifunctionality,” Proceedings of the National Academy of Sciences, 111(14), 5266-5270.
- ↩van der Sande, M. T., Poorter, L., Balvanera, P., Kooistra, L., Thonicke, K., Boit, A., … & Kolb, M. (2017). “The integration of empirical, remote sensing and modelling approaches enhances insight in the role of biodiversity in climate change mitigation by tropical forests,” Current Opinion in Environmental Sustainability, 26, 69-76.
- ↩Tilman, D., Isbell, F., & Cowles, J. M. (2014). “Biodiversity and ecosystem functioning,” Annual review of ecology, evolution, and systematics, 45.
- ↩Tilman, D., Reich, P. B., & Isbell, F. (2012). Biodiversity impacts ecosystem productivity as much as resources, disturbance, or herbivory. Proceedings of the National Academy of Sciences, 109(26), 10394-10397.
- ↩Altieri, M. A. (1999). “The ecological role of biodiversity in agroecosystems.” In Invertebrate Biodiversity as Bioindicators of Sustainable Landscapes(pp. 19-31).
- ↩Ajtay, G. L., et al. (1979). The Global Carbon Cycle(SCOPE-13).
- ↩Donato, D. C., Kauffman, J. B., Murdiyarso, D., Kurnianto, S., Stidham, M., & Kanninen, M. (2011). “Mangroves among the most carbon-rich forests in the tropics,” Nature geoscience, 4(5), 293.
- ↩Poungparn, S., & Komiyama, A. (2013). “Net ecosystem productivity studies in mangrove forests,” Reviews in Agricultural Science, 1, 61-64.
- ↩Ajtay, The Global Carbon Cycle.
- ↩Janzen, H. H. (2004). Carbon cycling in earth systems—a soil science perspective. Agriculture, Ecosystems & Environment, 104(3), 399-417.
- ↩Grace, J. (1999). “Carbon fluxes and productivity of tropical rainforests.” In Terrestrial Global Productivity: past, present and future. Academic Press, San Diego.
- ↩Donato, D. C., Kauffman, J. B., Murdiyarso, D., Kurnianto, S., Stidham, M., & Kanninen, M. (2011). “Mangroves among the most carbon-rich forests in the tropics.” Nature geoscience, 4(5), 293.
- ↩Komiyama, A., Ong, J. E., & Poungparn, S. (2008). “Allometry, biomass, and productivity of mangrove forests: A review.” Aquatic Botany, 89(2), 128-137.
- ↩Baccini, A., et. al. (2017). “Tropical forests are a net carbon source based on aboveground measurements of gain and loss.” Science, 358(6360), 230-234.
- ↩Watts, Jonathan.“Alarm as study reveals world’s tropical forests are huge carbon emission source,”Guardian, September 28, 2017.
- ↩Watts, Jonathan.“Alarm as study reveals world’s tropical forests are huge carbon emission source.”
- ↩Ward, D. S., & Mahowald, N. M. (2015). Local sources of global climate forcing from different categories of land use activities. Earth System Dynamics, 6(1), 175.
- ↩Tian, H., et al. (2016). The terrestrial biosphere as a net source of greenhouse gases to the atmosphere. Nature, 531(7593), 225.
- ↩Manna, M. C., Rao, A. S., & Mandal, A. (2015). “Impact of agricultural land management practices on soil carbon sequestration,” Indian Journal of Soil Conservation, 43(3), 204-212.
- ↩Nielsen, U. N., Ayres, E., Wall, D. H., & Bardgett, R. D. (2011). “Soil biodiversity and carbon cycling: a review and synthesis of studies examining diversity–function relationships.” European Journal of Soil Science, 62(1), 105-116.
- ↩Le Quéré, C., et. al. (2017). Global carbon budget 2017. Earth System Science Data Discussions, 1-79.
- ↩Don, A., Schumacher, J., & Freibauer, A. (2011). “Impact of tropical land‐use change on soil organic carbon stocks–a meta‐analysis.” Global Change Biology, 17(4), 1658-1670.
- ↩Magdoff, F. (2018). Personal communication.
- ↩Janzen, H. H. (2004). “Carbon cycling in earth systems—a soil science perspective.” Agriculture, Ecosystems & Environment, 104(3), 399-417.
- ↩Magdoff, F. (2018). Personal communication.
- ↩Küstermann, B., Munch, J. C., & Hülsbergen, K. J. (2013). “Effects of soil tillage and fertilization on resource efficiency and greenhouse gas emissions in a long-term field experiment in Southern Germany.” European journal of agronomy, 49, 61-73.
- ↩Liu, S. et al. (2014). Baseline and projected future carbon storage, carbon sequestration, and greenhouse-gas fluxes in terrestrial ecosystems of the eastern United States. Chapter, 7, 115-156.
- ↩Houghton, R. A. (1999). “The annual net flux of carbon to the atmosphere from changes in land use 1850–1990”Tellus B, 51(2), 298-313.
- ↩Le Quéré, C., Global carbon budget 2017.
- ↩Nelson, R. G., Hellwinckel, C. M., Brandt, C. C., West, T. O., De La Torre Ugarte, D. G., & Marland, G. (2009). “Energy use and carbon dioxide emissions from cropland production in the United States, 1990–2004,” Journal of environmental quality, 38(2), 418-425.
- ↩“Our Story,” Center for Carbon Removal.