# Ecology, Climate Change and Related News

1. ## New World Atlas of Desertification shows unprecedented pressure on planet’s resources; Over 75% of the Earth’s land area is already degraded

• The World Desertification Atlas by the European Commission’s Joint Research Centre provides the first comprehensive, evidence-based assessment of land degradation at a global level and highlights the urgency to adopt corrective measures.

June 21, 2018 European Commission Joint Research Centre Read full ScienceDaily article here

The … new edition of the World Atlas of Desertification, offering a tool for decision makers to improve local responses to soil loss and land degradation. The main findings show that population growth and changes in our consumption patterns put unprecedented pressure on the planet’s natural resources:

• Over 75% of the Earth’s land area is already degraded, and over 90% could become degraded by 2050.
• Globally, a total area half of the size of the European Union (4.18 million km²) is degraded annually, with Africa and Asia being the most affected.
• The economic cost of soil degradation for the EU is estimated to be in the order of tens of billions of euros annually.
• Land degradation and climate change are estimated to lead to a reduction of global crop yields by about 10% by 2050. Most of this will occur in India, China and sub-Saharan Africa, where land degradation could halve crop production.
• As a consequence of accelerated deforestation it will become more difficult to mitigate the effects of climate change
• By 2050, up to 700 million people are estimated to have been displaced due to issues linked to scarce land resources. The figure could reach up to 10 billion by the end of this century….
2. ## 25% of food producers contribute ~53% of that product’s environmental impacts; lower impact animal products have higher environmental impact than vegetable equivalents per new SCIENCE study

• Impacts of the lowest-impact animal products typically exceed those of vegetable substitutes, providing new evidence for the importance of dietary change.
• Cumulatively, our findings support an approach where producers monitor their own impacts, flexibly meet environmental targets by choosing from multiple practices, and communicate their impacts to consumers.
• A small number of producers create much of the impact. Just 15% of beef production creates ~1.3 billion tonnes of CO2 equivalents and uses ~950 million hectares of land.
• Across all products, 25% of producers contribute on average 53% of each product’s environmental impacts [across 5 indicators: GHG emissions, land use, terrestrial acidification,eutrophication, and scarcity-weighted freshwater withdrawals]. This variation and skew highlights potential to reduce impacts and enhance productivity in the food system.
• Researchers found that the variability in the food system fails to translate into animal products with lower impacts than vegetable equivalents. For example, a low-impact (10th percentile) litre of cow’s milk uses almost two times as much land and creates almost double the emissions as an average litre of soymilk.
• Reducing consumption of animal products by 50% by avoiding the highest-impact producers achieves 73% of the previous scenarios GHG emission reduction for example.
• Irrigation returns less water to rivers and groundwater than industrial and municipal uses and predominates in water-scarce areas and times of the year, driving 90 to 95% of global scarcity weighted water use
• Further, lowering consumption of discretionary products (oils, alcohol, sugar, and stimulants) by 20% by avoiding high-impact producers reduces the greenhouse gas emissions of these products by 43%. This creates a multiplier effect, where small behavioural changes have large consequences for the environment
• Communicating average product impacts to consumers enables dietary change and should be pursued

May 31, 2018 University of Oxford Read full ScienceDaily article here

Read Guardian UK article on this study here: Avoiding meat and dairy is ‘single biggest way’ to reduce your impact on Earth

New research highlights the environmental impacts of thousands of food producers and their products, demonstrating the need for new technology to monitor agriculture and environmental labels on food products.

They found large differences in environmental impact between producers of the same product. High-impact beef producers create 105kg of CO2 equivalents and use 370m2 of land per 100 grams of protein, a huge 12 and 50 times greater than low-impact beef producers. Low-impact beef producers then use 36 times more land and create 6 times more emissions than peas.

Aquaculture, assumed to create relatively little emissions, can emit more methane, and create more greenhouse gases than cows per kilogram of liveweight. One pint of beer, for example, can create 3 times more emissions and use 4 times more land than another. This variation in impacts is observed across all five indicators they assess, including water use, eutrophication, and acidification. [5 indicators: GHG emissions, land use, terrestrial acidification,
eutrophication, and scarcity-weighted freshwater withdrawals]

“Two things that look the same in the shops can have very different impacts on the planet. We currently don’t know this when we make choices about what to eat. Further, this variability isn’t fully recognised in strategies and policy aimed at reducing the impacts of farmers.” says Joseph Poore from the Department of Zoology and the School of Geography and Environment.

…Specifically the researchers found that the variability in the food system fails to translate into animal products with lower impacts than vegetable equivalents. For example, a low-impact (10th percentile) litre of cow’s milk uses almost two times as much land and creates almost double the emissions as an average litre of soymilk.

….Reducing consumption of animal products by 50% by avoiding the highest-impact producers achieves 73% of the previous scenarios GHG emission reduction for example. Further, lowering consumption of discretionary products (oils, alcohol, sugar, and stimulants) by 20% by avoiding high-impact producers reduces the greenhouse gas emissions of these products by 43%. This creates a multiplier effect, where small behavioural changes have large consequences for the environment….

J. Poore, T. Nemecek. Reducing food’s environmental impacts through producers and consumers. Science, 2018 DOI: 10.1126/science.aaq0216

## Abstract

Food’s environmental impacts are created by millions of diverse producers. To identify solutions that are effective under this heterogeneity, we consolidated data covering five environmental indicators; 38,700 farms; and 1600 processors, packaging types, and retailers. Impact can vary 50-fold among producers of the same product, creating substantial mitigation opportunities. However, mitigation is complicated by trade-offs, multiple ways for producers to achieve low impacts, and interactions throughout the supply chain. Producers have limits on how far they can reduce impacts. Most strikingly, impacts of the lowest-impact animal products typically exceed those of vegetable substitutes, providing new evidence for the importance of dietary change. Cumulatively, our findings support an approach where producers monitor their own impacts, flexibly meet environmental targets by choosing from multiple practices, and communicate their impacts to consumers.

From the paper:

….Today’s food supply chain creates ~1 3.7 billion metric tons of carbon dioxide equivalents (CO2eq), 26% of anthropogenic GHG emissions. A further 2.8 billion metric tons of CO2eq (5%) are caused by nonfood agriculture and other drivers of deforestation(17). Food production creates ~32% of global terrestrial acidification and ~78% of eutrophication. These emissions can fundamentally alter the species composition of natural ecosystems, reducing biodiversity and ecological resilience (19). The farm stage dominates, representing 61% of food’s GHG emissions (81%including deforestation), 79% of acidification, and 95% of eutrophication (table S17). Today’s agricultural system is also incredibly resource intensive, covering ~43% of the world’s ice- and desert-free land. Of this land, ~87% is for food and 13% is for biofuels and textile crops or is allocated to nonfood uses such as wool and leather.We estimate that two-thirds of freshwater withdrawals are for irrigation. However, irrigation returns less water to rivers and groundwater than industrial and municipal uses and predominates in water-scarce areas and times of the year, driving 90 to 95% of global scarcity weighted water use (17).

….Communicating average product impacts to consumers enables dietary change and should be pursued. Though dietary change is realistic for any individual, widespread behavioral change will be hard to achieve in the narrow time frame remaining to limit global warming and prevent further, irreversible biodiversity loss. Communicating producer impacts allows access to the second scenario, which multiplies the effects of smaller consumer changes.

3. ## Land-use change interacts with climate to determine species redistribution

• How species respond to both habitat loss and changing climates should be considered carefully for effective conservation and management of biodiversity.
• Some species may be able to move (and do move) in response to climate change and/or land-use change. Those species that are unable to respond effectively to warming or habitat loss face a high risk of extinction.
• The results show that tropical species may be especially vulnerable to the dual effects of climate and land-use changes.

May 7, 2018 The University of Hong Kong Read ScienceDaily article here

Climate change is altering where species live all over the planet. With global warming, species are moving towards the poles and up elevation where temperature is lower. However, along with global climate change, the world is also experiencing massive changes in land use which may also impact where species live. Could both of these forces be influencing current changes in species distributions?

…Increasing documentation of evidence for species redistribution under climate change in recent years made this research possible. “While the importance of land-use change for climate-driven species shifts has long been recognized, how land-use change is important or to what extent it affects species redistribution was never fully appreciated” noted Miss Guo. “Most of the studies we reviewed in this work stated that land-use remained unchanged over time while the data suggested otherwise and our results showed that these changes may have important implications.”…

Fengyi Guo, Jonathan Lenoir, Timothy C. Bonebrake. Land-use change interacts with climate to determine elevational species redistribution. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-03786-9

4. ## Biodiversity and nature’s benefits continue dangerous decline, scientists warn; Destruction of nature as dangerous as climate change, scientists warn

• Unsustainable exploitation of the natural world threatens food and water security of billions of people, major UN-backed biodiversity study reveals
• 75% of Earth’s land areas are degraded– new report warns that environmental damage threatens the well-being of 3.2 billion people. Yet solutions are within reach.
• Climate change will be the fastest-growing cause of species loss in the Americas by midcentury, according to this new set of reports from the leading global organization on ecosystems and biodiversity.
• Rapid expansion and unsustainable management of croplands and grazing lands is the main driver of land degradation, causing significant loss of biodiversity and impacting food security, water purification, the provision of energy, and other contributions of nature essential to people. This has reached “critical levels” in many parts of the world…Wetlands have been hit hardest, with 87 percent lost globally in the last 300 years…Wetlands continue to be destroyed in Southeast Asia and the Congo region of Africa, mainly to plant oil palm.
• Landmark reports highlight options to protect and restore nature and its vital contributions to people.

March 23 2018 Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) See National Geographic story here; See GuardianUK news coverage here;  Read ScienceDaily article here

Biodiversity — the essential variety of life forms on Earth — continues to decline in every region of the world, significantly reducing nature’s capacity to contribute to people’s well-being. This alarming trend endangers economies, livelihoods, food security and the quality of life of people everywhere, according to four landmark science reports written by more than 550 leading experts, from over 100 countries.

• Projections include:
• The unprecedented growth in consumption, demography and technology will roughly quadruple the global economy in the first half of the twenty-first century.
• Unless urgent and concerted action is taken, land degradation will worsen in the face of population growth, unprecedented consumption, an increasingly globalized economy, and climate change.
• Land degradation and climate change are likely to force 50 to 700 million people to migrate by 2050.
• By 2050, land degradation and climate change will reduce crop yields by an average of 10% globally, and up to 50% in certain regions.
• The capacity of rangelands to support livestock will continue to diminish in the future, due to both land degradation and loss of rangeland area.
• Biodiversity loss is projected to reach 38–46% by 2050.
• Opportunities to accelerate action identified in the report include:
• Improving monitoring, verification systems and baseline data;
• Coordinating policy between different ministries to simultaneously encourage more sustainable production and consumption practices of land-based commodities;
• Eliminating ‘perverse incentives’ that promote land degradation and promoting positive incentives that reward sustainable land management; and
• Integrating the agricultural, forestry, energy, water, infrastructure and service agendas.
• Remedial Options
1. National and international responses to land degradation are often focused on mitigating damage already caused….Land degradation is rarely, if ever, the result of a single cause and can thus only be addressed through the simultaneous and coordinated use of diverse policy instruments and responses at the institutional, governance, community and individual levels.
2. Land managers, including indigenous peoples and local communities, have key roles to play in the design, implementation and evaluation of sustainable land management practices.
3. Proven approaches to halting and reversing land degradation include:
• Urban planning, replanting with native species, green infrastructure development, remediation of contaminated and sealed soils (e.g. under asphalt), wastewater treatment and river channel restoration.
• Better, more open-access information on the impacts of traded commodities.
• Coordinated policy agendas that simultaneously encourage more sustainable consumption of land-based commodities.
• Eliminating perverse incentives that promote degradation – subsidies that reward overproduction, for example – and devising positive incentives that reward the adoption of sustainable land management practices.
• Rangelands:
• Land capability and condition assessments and monitoring
• Grazing pressure management
• Pasture and forage crop improvement
• Silvopastoral management
• Weed and pest management
• Rangelands with traditional grazing in many dryland regions have benefitted from maintaining appropriate fire regimes and the reinstatement or development of local livestock management practices and institutions. A variety of passive or active forest management and restoration techniques have successfully conserved biodiversity and avoided forest degradation while yielding multiple economic, social and environmental benefits.
• Combating land degradation resulting from invasive species involves the identification and monitoring of invasion pathways and the adoption of eradication and control measures (mechanical, cultural, biological and chemical).
• Responses to land degradation from mineral resource extraction include:
• on-site management of mining wastes (soils and water)
• reclamation of mine site topography
• conservation and early replacement of topsoil
• restoration and rehabilitation measures to recreate functioning grassland, forest, wetland and other ecosystems

4. Examples of well-tested practices and techniques, both traditional and modern, to halt degradation of agricultural lands include:

• Effective responses to avoid, reduce and reverse wetland degradation include:
• controlling point and diffuse pollution sources
• adopting integrated land and water management strategies; and
• restoring wetland hydrology, biodiversity, and ecosystem functions through passive and active restoration measures, such as constructed wetlands

Here is the America’s report from the IPBES- Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES).

By the numbers- The Americas:

Trends / data

• 13%: the Americas’ share of world’s human population
• 40%: share of world ecosystems’ capacity to produce nature-based materials consumed by people, and to assimilate by-products from their consumption
• 65%: the proportion of nature’s contributions to people, across all units of analysis, in decline (with 21% declining strongly)
• >50%: share of the Americas’ population with a water security problem
• 61%: languages and associated cultures, in trouble or dying out
• >95%: North American tall grass prairie grasslands transformed into human-dominated landscapes since pre-European settlement
• 72% and 66% respectively: of tropical dry forest in Mesoamerica and the Caribbean have been transformed into human-dominated landscapes since pre-European settlement
• 88%: Atlantic tropical forest transformed into human-dominated landscapes since pre-European settlement
• 17%: Amazon forest transformed into human-dominated landscapes since pre-European settlement
• 50%: decrease in renewable freshwater available per person since the 1960s
• 200-300%: Increase in humanity’s ecological footprint in each subregion of the Americas since the 1960s
• 9.5% and 25%: Forest areas lost in South America and Mesoamerica respectively since the 1960s
• 0.4% and 43.4%: net gains in forest areas in North America and the Caribbean respectively since the 1960s
• 1.5 million: approximate number of Great Plains grassland hectares loss from 2014 to 2015
• 2.5 million: hectares under cultivation in Brazil’s northeast agricultural frontier in 2013, up from 1.2 million ha in 2003, with 74% of these new croplands taken from intact cerrado (tropical savanna) in that region
• 15-60%: North American drylands habitat lost between 2000 and 2009
• >50%: US wetlands lost since European settlement (up to 90% lost in agricultural regions)
• >50%: decline in coral reef cover by the 1970s; only 10% remained by 2003

Economic value of nature’s contributions to people

• $24.3 trillion: estimated value per year of terrestrial nature’s contributions to people in the Americas (equivalent to the region’s gross domestic product) •$6.8, $5.3 and$3.6 trillion per year: nature’s contributions to people valued as ecosystem services in Brazil, USA and Canada respectively
• >$500 million: annual cost of managing the impacts of invasive alien zebra mussels on infrastructure for power, water supply and transportation in the Great Lakes…. 5. ## After California’s most destructive fire season, a debate over where to rebuild homes and best policies to reduce future costs Leave a Comment • In light of experience showing that wind-blown embers can carry fire into suburban areas, Cal Fire plans to revise the maps next year and will likely include even more neighborhoods • I would tell a zoning commission in Claremont or wherever, ‘Buy up the land before it gets built. And if a fire comes through, buy up the land so it won’t burn again.’ ” • As a condition of approval…the developer should establish a mechanism to require purchasers to pay for any increased fire protection that the property will require Doug Smith December 16 read full LA Times article here After a destructive wildfire swept from Calabasas to Malibu in 1993, the head of the Santa Monica Mountains Conservancy stood on a mountaintop on live TV and made a radical proposal. He called for a “three-strikes” rule to limit the number of times recovery funds could be spent to help rebuild a home destroyed by wildfire [Today] I think two strikes is enough and they ought to be bought out,” Edmiston said, after spending three days coordinating the conservancy’s crews on the Skirball, Rye and Creek fires. ….“I think what’s next is that every mayor, every town council and city planning board has to take this really seriously,” said Char Miller, professor of environmental analysis at Pomona College. “I would tell a zoning commission in Claremont or wherever, ‘Buy up the land before it gets built. And if a fire comes through, buy up the land so it won’t burn again.’ ”…. ….“In determining how or why or when homes should be rebuilt after a fire, it helps to have science on where homes should or shouldn’t be placed,” said Alexandra Syphard, senior research scientist at the nonprofit Conservation Biology Institute. “The science isn’t fully there yet.” The current standard for fire prediction is embodied in maps produced during the 2000s by the California Department of Forestry and Fire Protection. Largely based on vegetation and topography, the maps cover broad swaths of the state with gradations from moderate to very high fire hazard. In light of experience showing that wind-blown embers can carry fire into suburban areas, Cal Fire plans to revise the maps next year and will likely include even more neighborhoods…. Richard Halsey, director of the California Chaparral Institute, advocates holding local agencies financially responsible for fire losses of developments they approved. They should pay for all costs not covered by insurance and, if the owner rebuilds, all fire safety features, including exterior sprinkler systems….He favors methods to reverse the economic pressure, “everything from taking tracts of land at the urban periphery out of development, conservation easements. It might mean promoting higher insurance rates for homes built in high-risk areas such that the demand would go down.” …Edmiston said he has tallied 531 proposed new housing units being considered by the cities of Los Angeles and Calabasas in very high fire hazard zones in the Santa Monica Mountains. “We’re not talking about low income,” Edmiston said. “We’re talking about$1.5-million-plus homes.”

He proposes a linkage between the right to build and the inevitable cost of firefighting and recovery. As a condition of approval, he said, the developer should establish a mechanism to require purchasers to pay for any increased fire protection that the property will require.

“We’re talking about the climate change paradigm of the Santa Monica Mountains,” Edmiston said. “We’ve got to protect ourselves so that the rest of the city and the rest of the county don’t have to pay for putting these multimillion-dollar houses right next to the risk.”

6. ## How Improved Land Use Can Contribute to the 1.5°C Goal of the Paris Agreement

• The goals of the Paris Agreement cannot be met without
significant contributions from the land sector, including
supply-side measures in forestry and agriculture, and demand-
side measures related to healthier diets and reduced food waste.
• Through significant emissions reductions and carbon removals, the
land sector can contribute about 25 percent of the progress needed
to meet the 1.5°C goal formulated under the Paris Agreement.
• Land-sector emissions have to peak by 2020 and become net-zero
by 2040–50 and net-negative thereafter.

October 2017 Read full ClimateFocus article and report here

Climate Focus’ How Land Use Can Contribute to the 1.5°C Goal of the Paris Agreement develops a roadmap of action for the land-use sector to meet its necessary contribution to the Paris Agreement. The analysis relies on a modelling of land-sector development trajectories optimizing least-cost pathways, a bottom-up assessment of mitigation potentials, and a correction of potentials for political feasibility. The Global Biosphere Management Integrated Assessment Model, a partial-equilibrium model developed by the International Institute for Applied Systems Analysis, formed the basis of our modelling.

We determined the 40 countries with the highest technical mitigation potential and assessed the feasibility of mitigation action based on their political will and ability to realize this potential. Finally, we outlined 10 priority actions to reduce the land-use sector’s contribution to global warming. The actions range from avoided deforestation, restoration of forests, to diet shifts and reduced food waste.

…We developed a roadmap of action that relies on:

• effective forest protection (reduced deforestation)
• enhanced restoration
• sustainable forest management
• halting peatland burning
• peatland restoration
• a shift to healthier diets
• reduced food waste and losses
• enhanced soil carbon sequestration
• increased efficiency of synthetic fertilizer production and use
• reduced emissions from rice paddies
• reduced emissions from livestock (enteric fermentation)
7. ## Insectageddon: farming can be more catastrophic than climate breakdown

George Monbiot Friday 20 October 2017

…two other issues have such huge and immediate impacts that they push even this great predicament [of global warming] into third place.One is industrial fishing, which, all over the blue planet, is now causing systemic ecological collapse. The other is the erasure of non-human life from the land by farming.

And perhaps not only non-human life. According to the UN Food and Agriculture Organisation, at current rates of soil loss, driven largely by poor farming practice, we have just 60 years of harvests left. And this is before the Global Land Outlook report, published in September, found that productivity is already declining on 20% of the world’s cropland.

The impact on wildlife of changes in farming practice (and the expansion of the farmed area) is so rapid and severe that it is hard to get your head round the scale of what is happening. A study published this week in the journal Plos One reveals that flying insects surveyed on nature reserves in Germany have declined by 76% in 27 years. The most likely cause of this Insectageddon is that the land surrounding those reserves has become hostile to them: the volume of pesticides and the destruction of habitat have turned farmland into a wildlife desert….

8. ## Why Hurricane Irma Could Hurt, a Lot: increase in coastal development leaves much in harm’s way

….Central and South Florida have grown at a breathtaking pace since 1990, adding more than 6 million people. Glittering high-rises and condominiums keep sprouting up along Miami Beach and other coastal areas. A lot more valuable property now sits in harm’s way….

…But half of the expected rise in hurricane costs is the result of expected increases in coastal development. Today, according to the C.B.O., roughly 1.2 million Americans live in coastal areas at risk of “substantial damage” from hurricanes — defined as damage of at least 5 percent of average income. By 2075, that number is forecast to rise to 10 million.

Population growth can also increase hurricane risks by adding newcomers who are unfamiliar with big storms or by clogging roads during evacuations, experts said.

….As of Wednesday, forecasters were still unsure where Irma might make landfall in Florida or how strong it will be when it does. But in almost any conceivable scenario, a hurricane today is likely to do more damage than a comparable storm in the past, if only because of increased development….

9. ## Deforestation has double the effect on global warming than previously thought

• Even if all fossil fuel emissions are eradicated, if current rates of deforestation in the tropics continue through to 2100 then there will still be a 1.5 degree Celsius increase in global temperature
• While carbon dioxide emissions from energy use must be the primary target of climate change mitigation efforts, land use and land cover change (LULCC) also represent an important source of climate forcing.
• Tackling deforestation should be higher on the climate change agenda.

In the fight against climate change, much of the focus rests on reducing our dependence on fossil fuels and developing alternative energy sources. However, the results of a new study suggest that far more attention should be paid to deforestation and how the land is used subsequently – the effects of which make a bigger contribution to climate change than previously thought.

The research, conducted by Cornell University and published in the journal Environmental Research Letters,shows just how much this impact has been underestimated. Even if all fossil fuel emissions are eradicated, if current rates of deforestation in the tropics continue through to 2100 then there will still be a 1.5 degree Celsius increase in global temperature….

Natalie M Mahowald et al. Are the impacts of land use on warming underestimated in climate policy? Environmental Research Letters. August 2017. DOI: 10.1088/1748-9326/aa836d

Abstract: While carbon dioxide emissions from energy use must be the primary target of climate change mitigation efforts, land use and land cover change (LULCC) also represent an important source of climate forcing. In this study we compute time series of global surface temperature change separately for LULCC and non-LULCC sources (primarily fossil fuel burning), and show that because of the extra warming associated with the co-emission of methane and nitrous oxide with LULCC carbon dioxide emissions, and a co-emission of cooling aerosols with non-LULCC emissions of carbon dioxide, the linear relationship between cumulative carbon dioxide emissions and temperature has a two-fold higher slope for LULCC than for non-LULCC activities. Moreover, projections used in the Intergovernmental Panel on Climate Change (IPCC) for the rate of tropical land conversion in the future are relatively low compared to contemporary observations, suggesting that the future projections of land conversion used in the IPCC may underestimate potential impacts of LULCC. By including a “business as usual” future LULCC scenario for tropical deforestation, we find that even if all non-LULCC emissions are switched off in 2015, it is likely that 1.5°C of warming relative to the preindustrial era will occur by 2100. Thus, policies to reduce LULCC emissions must remain a high priority if we are to achieve the low to medium temperature change targets proposed as a part of the Paris Agreement. Future studies using integrated assessment models and other climate simulations should include more realistic deforestation rates and the integration of policy that would reduce LULCC emissions.

10. ## ﻿Soil carbon debt from 12,000 years of human land use

• global carbon debt due to agriculture of 133 Pg C [133 Gt (billion metric tons of C) or 488 Gt CO2e] for the top 2 m of soil, with the rate of loss increasing dramatically in the past 200 years
• assuming soil organic carbon (SOM) reaches a new steady state in 20 y (35, 44), this calculation suggests that 8 Pg C to 28 Pg C [up to 28 Gt (billion metric tons of C) or 103 Gt CO2e] or can be recaptured
• there are identifiable regions which can be targeted for SOC (soil organic carbon) restoration efforts
• [Note: Hansen et al 2017 calls for 150 Pg C or ~550 Gt CO2e extraction from atmosphere globally with massive greenhouse emissions reductions of 6%/year starting in 2021 to return to 350 PPM CO2 in atmosphere and to secure a safe climate (Holocene) for human civilization by 2100]
• [Sanderman high end scenario would be 19% of CO2e extraction needed to secure safe climate by 2100 per Hansen above]

Jonathan Sanderman, Tomislav Hengl and Gregory J. Fiske. Soil carbon debt of 12,000 years of human land use. PNAS September 5, 2017 vol. 114 no. 36 9575-9580

Abstract: Human appropriation of land for agriculture has greatly altered the terrestrial carbon balance, creating a large but uncertain carbon debt in soils. Estimating the size and spatial distribution of soil organic carbon (SOC) loss due to land use and land cover change has been difficult but is a critical step in understanding whether SOC sequestration can be an effective climate mitigation strategy. In this study, a machine learning-based model was fitted using a global compilation of SOC data and the History Database of the Global Environment (HYDE) land use data in combination with climatic, landform and lithology covariates. Model results compared favorably with a global compilation of paired plot studies. Projection of this model onto a world without agriculture indicated a global carbon debt due to agriculture of 133 Pg C for the top 2 m of soil, with the rate of loss increasing dramatically in the past 200 years. The HYDE classes “grazing” and “cropland” contributed nearly equally to the loss of SOC. There were higher percent SOC losses on cropland but since more than twice as much land is grazed, slightly higher total losses were found from grazing land. Important spatial patterns of SOC loss were found: Hotspots of SOC loss coincided
with some major cropping regions as well as semiarid grazing regions, while other major agricultural zones showed small losses and even net gains in SOC. This analysis has demonstrated that there are identifiable regions which can be targeted for SOC restoration efforts.

Implications: This analysis indicates that the majority of the used portions of planet Earth have lost SOC, resulting in a cumulative loss of ∼133 Pg C due to agricultural land use. These SOC losses are on par with estimates of carbon lost from living vegetation primarily due to deforestation (40) and are nearly 100 Pg C higher than earlier estimates of land use and land use change-driven losses of SOC (41). Importantly, as Fig. 1 demonstrates, there are hotspots of SOC loss, associated with extensive cropping regions but also with highly degraded grazing land (SI Appendix, Fig. S9), suggesting that there are identifiable regions which should be targets for SOC restoration efforts.

The potential to recover lost SOC may be more limited than is often assumed. The amount of SOC that has been lost historically can be thought of as the carbon sink potential of the soil (42). Our analysis has found that this sink potential is ∼133 Pg C (SI Appendix, Table S3). A widely repeated figure is that, with adoption of best management practices, two thirds of lost SOC can be recovered (42). If the two-thirds figure is accurate, then SOC sequestration has the potential to offset 88 Pg C (322 Pg CO2) of emissions. However, bottom-up estimates of the maximum biophysical potential for carbon sequestration on cropping and grazing land range from 0.4 Pg Cy−1 to 1.4 Pg Cy−1 (20, 43). Assuming SOC reaches a new steady state in 20 y (35, 44), this calculation suggests that 8 Pg C to 28 Pg C can be recaptured. Even the range of 8 Pg C to 28 Pg C is likely overly ambitious given the various social, economic, and technical constraints on universal adoption of best management practices (45), suggesting that the amount of the carbon sink that can be filled is on the order of, at best, 10 to 30% globally and may well be <10%.

Conclusions: Our data-driven statistical analysis confirms that agricultural land use is a significant driver of SOC levels. ….This analysis also demonstrated that not all land use is associated with large losses in SOC, particularly in regions with naturally infertile soils. These results provide a basis for national and international policies to target SOC restoration efforts but also suggest that more effort needs to be put into collecting, integrating, and using legacy soil profile data, especially historic data 50+ y old, so that even more reliable models of SOC dynamics can be produced.