Natural climate solutions, Griscom 2017
This is one of the most comprehensive mainstream studies to date of a broad spectrum of natural climate solutions by thirty-two co-authors and supported by The Nature Conservancy. The report examines “20 conservation, restoration, and/or improved land management actions that increase carbon storage and/or avoid greenhouse gas emissions across global forests, wetlands, grasslands, and agricultural lands.” The authors “find that the maximum potential of NCS [Natural Climate Solutions] —when constrained by food security, fiber security, and biodiversity conservation—is 23.8 petagrams of CO2 equivalent . . . This is ≥30% higher than prior estimates, which did not include the full range of options and safeguards considered here.” [Griscom 2017: 11645]. The study seeks to assess both the potential emissions from land use as well as the carbon-sequestration potential.
The study posits a target of <2o C as the conventionally agreed-upon safe limit:
Warming will likely be held to below 2 °C if natural pathways are implemented at cost-effective levels . . . and if we avoid increases in fossil fuel emissions for 10 y and then drive them down to 7% of current levels by 2050 and then to zero by 2095 [p. 11647]
The authors state that their estimates are intentionally conservative because (1) they do not include potential benefits of payments for high-money-value ecosystem services in stimulating NCS efforts; (2) they exclude various management practices where data were not “sufficiently robust for global extrapolation,” e.g., no-till, adaptive multi-paddock grazing, etc.; and (3) significant additional investment would be required to keep warming at 1.5o C. [Griscom 2017: 11648]
Detail is provided on contributions of specific mitigation pathways, such as forests, wetlands, grasslands, etc., and on challenges as well. For example, “Despite the large potential of NCS, land-based sequestration efforts receive only about 2.5% of climate mitigation dollars.” [Griscom 2017: 11648] This observation is consistent with our observations of limited available resources for the most basic NCS education. Other challenges include deforestation for farming and animal husbandry, losing high carbon sequestration benefits of wetlands due to reclamation, and impacts of climate feedbacks such as fire, drought, temperature increases, etc.
We applaud Griscom et al. for an excellent and comprehensive analysis and review of many of the factors in natural climate solutions. We do, however, believe that (1) the potential of nature’s solutions is far greater than Griscom et al. estimate, and (2) that the temperature limits (1.5o – 2o C) are too high and too dangerous – considering that natural processes are already changing, drastically and for the worse, with an average global temperature increase of barely 1o C (see Appendix A: Urgency of the Biodiversity and Climate Crisis).
The differences between the perspectives of Griscom et al. and those adopted in this Compendium are paradigmatic. Griscom et al. acknowledges that their estimates are conservative, looks at a set of studies that tends toward the mainstream and is primarily based on established and widespread practice. This is perfectly reasonable in the process of what Thomas Kuhn calls “normal science” (see Compendium Vol. 1 No. 1 for an extensive discussion of Kuhn’s landmark work). Unfortunately the process of normal science for accepting new thinking and discoveries usually takes decades, and we are currently in the throes of an extinction, and an emergency with respect to biodiversity, and climate change. Therefore we have to accelerate our response. Accordingly, Bio4Climate searches for studies that tend to examine positive variants, i.e., examples of what is possible beyond current conceptual boundaries. We emphasize goals to strive for, even if the data are not yet “sufficiently robust for global extrapolation.” The robustness of such data will increase with more intentional focus.
An interesting side effect of the paradigm difference is that numerous sources that we cite, many from the scientific literature, don’t appear in NCS references (for example, Richard Teague [Teague et al. 2016], Gabe Brown [Brown 2016], Tom Goreau [Goreau 2015], Rebecca Ryals and Whendee Silver [Ryals and Silver 2013], David Johnson [Johnson 2017], Paul and Elizabeth Kaiser [Kaiser 2017], Terry McCosker [McCosker 2000], Carol Evans and Jon Griggs [Evans et al., 2015], to name just a few). Nor are there discussions of permaculture or agroforestry, two of the more promising areas of research and practice in land management that lead to climate-positive results.
Unfortunately the process of normal science for accepting new thinking and discoveries usually takes decades, and we are currently in the throes of an extinction, and an emergency with respect to biodiversity, and climate change. Therefore we have to accelerate our response. Accordingly, Bio4Climate searches for studies that tend to examine positive variants, i.e., examples of what is possible beyond current conceptual boundaries. We emphasize goals to strive for, even if the data are not yet “sufficiently robust for global extrapolation.” The robustness of such data increases with intentional focus.
Drawdown, Hawken, ed. 2017
Edited by innovator and entrepreneur Paul Hawken, Drawdown is a remarkable and comprehensive work presenting eighty well-vetted solutions and twenty promising “coming attractions” to remove carbon from the atmosphere and restore planetary health. Hawken engaged numerous scientists, modellers, advisers, artists and writers, resulting in a beautifully illustrated and comprehensive exploration of possibilities for reversing global warming.
The impact of the book as a whole is as important as each solution: Drawdown presents a universe of actions that go far beyond what we can imagine if we consider only emissions reductions and alternative energy. It leads to an entirely different climate conversation from the one we’re used to, and offers many threads of hope.
Drawdown has something for everyone, covering sectors of Energy, Food, Buildings and Cities, Land Use, Transport, and Materials. Near the top of the list is Women and Girls, whose education has dramatic effects on population and is one of the most important climate positive steps we can take. Of course technology offerings abound, but they are amply balanced by discussions of biology and social change, often sorely missing in debates on global warming. Of particular interest in this Compendium are biological strategies; we’ll mention just three of them here.
Agroforestry in Burkina Faso
After terrible droughts in the 1980s resulted in a 20% reduction in rainfall and millions of deaths by starvation, farmer Yacouba Sawadogo enhanced a traditional practice of digging rain-capturing pits by adding manure. There were seeds in the manure and as a result trees began to grow, holding soils together with roots, protecting plantings from wind gusts that before had required frequent re-sowing, and opening channels that moved water into the soils and raised water tables. This foray into agro-forestry spread across the rural countryside to widespread beneficial effect.
Of great significance is that the expertise, invention and community organizing were native and local, required no foreign aid or expensive soil inputs, and in terms of money cost nothing. This is what sustainability can look like. [Hawken 2017: 118-120]
In 1979, after a devastating fire destroyed his two-thousand acre farm in Australia, Colin Seis began to question why crops and animals couldn’t be profitably raised on the same land, effectively doubling output. Persisting through a difficult transition, Seis saw water retention improvements, decreased input costs, a virtual end to insect infestation, and measures of soil fertility and carbon content go up along with profits. Today, pasture cropping is practiced on over two thousand Australian farms and is spreading throughout the world. [Hawken 2017: 175]
Silvopasture, the most common form of agroforestry, is the practice of combining trees and woody shrubs with pasture grasses. The result is healthier plant and animal growth, including sequestering a respectable one to four tons of carbon per acre. It is currently practiced on over one billion acres worldwide.
For remarkable next steps enter the intensive part of silvopasture, starting with a quickly growing, edible leguminous shrub, Leucaena leucocephala in Australia and Latin America (different species of shrubs are suitable in different ecosystems). Water retention improves, biomass increases, species biodiversity doubles, animal stocking rates almost triple, ambient temperatures decrease by 14 to 23 degrees F in the tropics, meat production increases by a factor of 4 to 10, and perhaps most strikingly, soil carbon sequestration rates have exceeded 10 tons per acre (conventional agriculture can claim 1 ton of carbon per acre or less, or even net carbon loss to the atmosphere). [Hawken 2017: 181]
Intertidal resource use over millennia enhances forest productivity, Trant 2016
Abstract: Human occupation is usually associated with degraded landscapes but 13,000 years of repeated occupation by British Columbia’s coastal First Nations has had the opposite effect, enhancing temperate rainforest productivity. This is particularly the case over the last 6,000 years when intensiﬁed intertidal shellﬁsh usage resulted in the accumulation of substantial shell middens. We show that soils at habitation sites are higher in calcium and phosphorous. Both of these are limiting factors in coastal temperate rainforests. Western red cedar (Thuja plicata) trees growing on the middens were found to be taller, have higher wood calcium, greater radial growth and exhibit less top die-back. Coastal British Columbia is the ﬁrst known example of long-term intertidal resource use enhancing forest productivity and we expect this pattern to occur at archaeological sites along coastlines globally [Trant 2016: 1].
Although focused on forests and not farmland, this study shows that, as in the Amazon, where indigenous people created SOM-rich terra preta soil (akin to biochar-enhanced soil), human populations can increase soil quality and ecosystem productivity beyond what the potential would have been absent human activity.
This is an interesting point with respect to global potential for soil carbon sequestration. Scientists often refer to an equilibrium point, up to which soils can regain carbon previously lost through exploitive human activity. Equilibrium is generally seen as being the point at which new SOC levels are equivalent to or somewhat less than what they were prior to human exploitation of the soil, and never greater than the original amount. While Trant et al.  have found evidence of calcium and phosphorus (not carbon) enrichment due to human activity, their findings raise questions about the extent to which intentionally building soils through all the methods we know to maximize carbon storage could increase various soils’ presumed equilibrium points.
Human occupation is usually associated with degraded landscapes but 13,000 years of repeated occupation by British Columbia’s coastal First Nations has had the opposite effect, enhancing temperate rainforest productivity [Trant 2016: 1].
The ecology of soil carbon: pools, vulnerabilities, and biotic and abiotic controls, Jackson 2017
This review examines “the state of knowledge for the stocks of, inputs to, and outputs from SOM around the world” [Jackson 2017: 422], with a view toward developing better understanding of processes that stabilize SOM. It explains the biological processes involved in carbon cycling and storage, finding that “root inputs are approximately ﬁve times more likely than an equivalent mass of aboveground litter to be stabilized as SOM” [Jackson 2017: 420]. Litter input can either increase or decrease SOM, despite the assumption in most carbon models that there is a linear relationship between litter input and transformation of carbon into more stable forms. This finding suggests that perennials and other deep-rooting plants have an important role to play with respect to carbon sequestration. As the author puts it:
Managing carbon inputs and relative allocation, for instance, through selection for deep roots or for greater belowground allocation in crops (Kell 2011), has been suggested as a way to increase SOM formation and stabilization in such systems (Bolinder et al. 2007, Eclesia et al. 2016). However, plant breeding has traditionally selected for aboveground yields alone; therefore, potential trade-offs between yield and root production must be carefully evaluated (DeHaan et al. 2005). New tools for monitoring root systems and in situ SOM in the ﬁeld are needed (Molon et al. 2017) [Jackson 2017: 422]. . . .
The importance of root inputs for SOM formation is likely attributable to both their chemical composition and, almost certainly, their presence in the soil; upon death, they immediately interact with soil minerals, microbes, and aggregates. Roots tend to be characterized more by aliphatic compounds that are readily sorbed to mineral surfaces, and their composition (and that of root exudates) can increase microbial carbon use efﬁciency (CUE), deﬁned as the ratio of microbial growth to carbon uptake, more than litter can. High CUE promotes microbial growth and carbon stabilization in mineral-associated soil pools, and low CUE favors biomass respiration (Manzonietal.2012a) [Jackson 2017: 423]. . . .
Soils hold the largest biogeochemically active terrestrial carbon pool on Earth and are critical for stabilizing atmospheric CO2 concentrations. Nonetheless, global pressures on soils continue from changes in land management, including the need for increasing bioenergy and food production [Jackson 2017: 420].
. . . plant breeding has traditionally selected for aboveground yields alone; therefore, potential trade-offs between yield and root production must be carefully evaluated [Jackson 2017].
National comparison of the total and sequestered organic matter contents of conventional and organic farm soils, Ghabbour 2017
An analysis of hundreds of soil samples collected from organic and conventional farms around the US shows higher average percentages both of total SOM and of humic substances – a measure of carbon sequestration – for organic farm soils compared to conventional farm soils. The mean percent humification (humic substances divided by total SOM) for organic soils is 57.3%, compared to 45.6% for conventional soils.
Agroforestry strategies to sequester carbon in temperate North America, Udawatta & Jose 2012
This meta-analysis estimates total carbon sequestration potential in the US from various agroforestry practices to be 530 TgC/year (530 million metric tons), equivalent to about 1/3 of annual US carbon emissions from fossil fuel combustion. Based on their literature review, the authors estimate per-hectare sequestration rates (based on aboveground and belowground carbon accumulation) for each practice as follows: 6.1t C/ha/yr (silvopastoral), 3.4t C/ha/yr (alleycropping), 6.4t C/ha/yr (windbreaks), 2.6t C/ha/yr (riparian buffer).
Compost, manure and synthetic fertilizer influences crop yields, soil properties, nitrate leaching and crop nutrient content, Hepperly 2009
A sequestration rate of 2.363t C/ha/yr was demonstrated where compost made of dairy manure and leaves was applied to fields in a three year rotation of corn-vegetable-small grain, with leguminous cover crops. The same rotation treated with chemical fertilizer instead of compost resulted in a net loss of -0.317t C/ha/yr.
Legume-based cropping systems have reduced carbon and nitrogen losses, Drinkwater 1998
This study compared three corn-soybean cropping systems: (1) conventional 2-yr rotation with chemical inputs, and residues returned to soil; (2) a longer (than 2 years), organic rotation with grass/legume hayed and returned to soil in manure; and (3) a longer (than 2 years) organic rotation with grass/legume turned back into the soil directly. Even though the conventional system returned more total residue to the soil, carbon sequestration was significantly lower for the conventional system than for the two organic, legume-based systems. Authors suggest that this is due to greater temporal plant diversity from the longer rotations, and higher quality residue (greater N:C) in the two legume-based organic systems. Furthermore, CO2 emissions were lower in the legume-based organic systems due to 50% lower energy use.
Even though the conventional system returned more total residue to the soil, carbon sequestration was significantly lower for the conventional system than for the two organic, legume-based systems. Authors suggest that this is due to greater temporal plant diversity from the longer rotations, and higher quality residue (greater N:C) in the two legume-based organic systems. [Drinkwater]
Brown, Gabe, 2016, Regeneration of our Lands: A Producer’s Perspective, TedX Grand Forks, https://youtu.be/QfTZ0rnowcc.
Evans, Carol, Jon Griggs, Jim Laurie 2015, Miracle in the Nevada Desert, Restoring Water Cycles to Reverse Global Warming, Biodiversity for a Livable Climate, Tufts University, October 18, 2015 https://www.youtube.com/watch?v=lR7w9Tritj8&feature=youtu.be.
Goreau, Thomas, Ronal Larson and Joanna Campe, eds. 2015, Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase, CRC Press, https://www.crcpress.com/Geotherapy-Innovative-Methods-of-Soil-Fertility-Restoration-Carbon-Sequestration/Goreau-Larson-Campe/p/book/9781466595392.
Griscom, B.W. et al., 2017, Natural Climate Solutions, PNAS October 31, 2017, 114:44, 11645–11650, www.pnas.org/cgi/doi/10.1073/pnas.1710465114
Hawken, Paul, Ed., 2017, Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming, Penguin Books, http://www.drawdown.org/.
Jackson, Robert B., et al, 2017, The Ecology of Soil Carbon: Pools, Vulnerabilities, and Biotic and Abiotic Controls, Annual Review of Ecology, Evolution, and Systematics 48:419–45, https://www.annualreviews.org/doi/abs/10.1146/annurev-ecolsys-112414-054234.
Johnson, David, 2017, Regenerating the Diversity of Life in our Soils – Hope for Farming and Climate, https://youtu.be/neIIPRRnXQQ; and Soils Beneath Our Feet: Can Regenerative Agriculture and Healthy Soils Help Combat Climate Change, https://www.youtube.com/watch?v=XlB4QSEMzdg.
Kaiser, Paul and Elizabeth 2017, No-till Farmers Elizabeth and Paul Kaiser Keynote 2017 NOFA/Mass Winter Conference, https://www.youtube.com/watch?v=zAn5YxL1PbM.
McCosker, Terry 2000, Cell Grazing - The First Ten Years in Australia, Tropical Grasslands, Volume 34, 207-218, https://www.tropicalgrasslands.asn.au/Tropical%20Grasslands%20Journal%20archive/PDFs/Vol_34_2000/Vol_34_03-04_00_pp207_218.pdf
Ryals, Rebecca, Whendee Silver 2013, Effects of organic matter amendments on net primary productivity and greenhouse gas emissions in annual grasslands, Ecological Applications, 23(1), http://www.c-agg.org/cm_vault/files/docs/38/ryals_and_silver_ecoapps2013.pdf.
Teague, W.R., Steve Apfelbaum, Rattan Lal et al. 2016, The role of ruminants in reducing agriculture’s carbon footprint in North America, J. Soil and Water Conservation, March/April 2016, 71:2, http://www.jswconline.org/content/71/2/156.abstract.
Trant, Andrew, et al, 2016, Intertidal resource use over millennia enhances forest productivity, Nature Communications 7:12491, https://www.nature.com/articles/ncomms12491.