For avoided emissions from energy, we leverage a climate model developed by Teske et al. (2019) for One Earth. The One Earth model establishes that it is possible to stay within the carbon budget for 1.5 degrees Celsius of warming with a massive transformation of how we create and use energy paired with a global land restoration campaign. The estimates for renewable energy technologies (solar, wind, geothermal) are based on the amount of non-renewable energy sources that need to be displaced to stay in line with 1.5C. Estimates for the overarching sectors (industry, buildings, mobility) reflect the avoided emissions from using less energy, both through efficiency gains and overall reduced energy demand. All energy system avoided emissions are relative to a 5 degrees Celsius business-as-usual reference scenario. Importantly, the One Earth model is not cost optimized and cannot easily attribute mitigation potential to specific actions. The numbers should be considered primarily a portrayal of what is possible and necessary.
For ecosystem-based solutions, regenerative agriculture, and clean cookstoves, we leverage the landmark Natural Climate Solutions paper by Griscom et al. (2017). We assume a 10 year ramp up period to the maximum potential mitigation rate of all solutions presented in the study. Though the maximum mitigation rates are not cost-optimized, they do incorporate limitations based on food production needs, fuel needs, and biodiversity. The reference cases for these nature-based solutions are business-as-usual ecosystem degradation rates. It is worth noting that the true potential of regenerative agriculture as a holistic practice may be understated by the estimates provided in the Griscom paper. The content of the book discusses cutting edge breakthroughs and rediscoveries of age-old solutions that dramatically heal soil, and we believe that scientific assessments of these practices have yet to grasp their full potential.
Three food-system solutions – Eating Everything, Wasting Nothing, and Compost – are based our analysis of potential food production and waste patterns over time, leveraging food production emissions compiled by Poore and Nemecek (2018), food waste data from ReFED, and landfill emissions data from WRI’s CAIT dataset. The projected dietary changes tied to Eating Everything temper the maximum potential of Griscom’s Regenerative Agriculture pathways because fewer cattle means less cattle emissions to mitigate. Estimates for Seaforestation and Azolla Fern are based on our own analyses leveraging multiple sources. Seaforestation is primarily based on studies by Froehlich et al. (2019) and Han et al. (2017). Estimates for Azolla build off of van der Heide et al. (2006). Estimates for Carbon Architecture are based on a studie by Galina et al. (2020).
What we didn’t quantify
Some solutions discussed in Regeneration are not reflected in the final tally of summary potential. In most cases, the solutions left off have no readily quantifiable impact on the future temperature of our planet.[1] Some solutions – particularly Animal Integration and Vermiculture – have documented potential but no large scale assessments in the literature. Other solutions are reflected in the final tally but are fully encapsulated by other line items,[2] or are overarching categories that cover multiple solutions.[3] Enabling technologies in the forecasted energy system transition – such as Storage and Microgrids – are critical to the success of the broader transformation but not directly associated with avoided emissions. Electrifying Everything is similarly a key strategy, and responsible for much of the avoided emissions in Industry, Buildings, and Mobility (see Electric Vehicles), but is not included in the list to avoid double counting.
There are some solutions that we would like to include but have opted not to for methodological clarity. The avoided emissions of protecting Boreal Forests are difficult to quantify because of “albedo” tradeoffs – essentially, when you cut down boreal forests and expose snow-covered ground, the reflectivity of the snow cools the Earth about as much as the lost carbon stocks warm the Earth. Though the short term accounting on the boreal’s contribution to global warming is unclear, particularly at higher latitudes, there are countless other reasons to protect the boreal – safeguarding biodiversity and protecting indigenous homelands are two among many. Bamboo and Afforestation are solutions that have significant potential to provide sustainable fiber and restore degraded land, with appropriate safeguards against monoculture practices, invasiveness, and planting on land that would be best restored to its natural state. However, areas that could be used for Bamboo and Afforestation are fully utilized for other restoration-focused solutions in the Griscom et al. framework.
Refrigerant management has been touted as among the most cost effective ways to dramatically curb global warming. We believe the world can and should tightly manage refrigerants, but because the issue is so far removed from individual action - besides pressuring our local supermarkets or advocating for better policies – we have opted not to cover it here.
Lastly, there are some solutions that we have chosen not to quantify because we believe quantification inappropriately reduces complex topics. Ensuring universal access to education and healthcare for women has frequently been tied to a perceived need for limiting population growth. While it is possible to estimate a potential emissions reduction from education, we believe these basic rights are worth ensuring regardless of the impact on our climate, and that the developing regions targeted by this discourse have every right to increase their carbon emissions in pursuit of a higher quality of life – they are not anywhere near the top of the list of those responsible for managing their footprints. Similarly, it is frequently noted that land managed by indigenous peoples holds disproportionately high levels of biodiversity, and that indigenous forest tenure is the most effective way to protect terrestrial carbon stocks. While this is true, we believe that returning land to indigenous peoples is an invaluable end in and of itself.
Carbon stock methodology
Global estimates of organic carbon stocks, particularly soil carbon, are notoriously imprecise. The estimate of total soil organic carbon stocks provided in the table - ~3,300 gigatons – is on the higher side of older estimates (from the late ‘90s and early 2000’s) made prominent in the IPCC’s Fifth Assessment Report. As of this writing, at least two new maps of global soil carbon down to 1 meter depth are about to be released and will present significant strides forward in our understanding of terrestrial carbon.
Our estimates for terrestrial organic carbon stock were synthesized from multiple spatial and non-spatial datasets into one consolidated global map. The map was built on three types of data: 1) ecosystem extents, 2) biomass, to account for the carbon stored in trees, roots, and other organic matter, and 3) soil organic carbon stock estimates down to 1 meter depth. The map leverages data from The World Wildlife Fund for ecosystem extents, a soil carbon map published by Tom Hengl and Ichsani Wheeler, and a biomass map from Seth Spawn and team. Many other datasets were pulled in for smaller pieces of the pie – seagrasses (1, 2), mangroves (1, 2, 3, 4 ) , salt marshes (1, 2), peat(1, 2, 3), wetlands (1), and conversions (1, 2). The design of the analysis was inspired and guided by peers at Conservation International led by Monica Noon and Allie Goldstein (paper to be publish).
Throughout this book, carbon stocks refer to soil organic carbon down to just 1 meter depth, plus living biomass. The only exception is peat – when the book references total peat carbon stocks, it is referring to an estimate of total peat carbon stocks beyond 1 meter depth (peat stocks have been known to be as deep as 15 meters or more), even though that full peat estimate is not included in our total terrestrial carbon estimate for consistency. Peat is found in multiple biomes and is included throughout the individual ecosystem numbers in the summary carbon table. The estimates for total carbon stocks and primary ecosystems only include peat stocks down to 1 meter depth for consistency with other ecosystems, both in the summary table and throughout the book. Similarly, because wetlands encompass mangroves, saltmarshes, and peatlands, and because they intersect with multiple terrestrial ecosystems, they have been excluded from this summary table for clarity. Apart from mangroves and salt marshes, non-peat wetlands encompass 55 gigatons of carbon globally.
Throughout the book, “tropical” refers to both tropical and subtropical ecosystems. “Terrestrial” carbon stocks include all land-based biomes and coastal biomes including mangroves, seagrasses, and salt marshes. The total land area considered is all ice-free land – this excludes Antarctica and areas of permanent ice cover, but not permafrost.
[1] Rainmakers; Trophic Cascades; Rewilding Pollinators; Grazing Ecology; Beavers; Urban Farming; The Nature of Cities; Localization; Decommodification; Insect Extinction; War Industry; Poverty Industry; Women and Food
[2] Proforestation; Fire Ecology; Walkable City; Eating Trees; Big Food; Banking Industry; Politics Industry; Clothing Industry; Healthcare Industry; Plastics
[3] Wildlife Corridors; Degraded Land Restoration; Marine Protected Areas; Net Zero Cities; Wetlands