The Land Use Sector includes the protection and restoration of high-carbon ecosystems such as forests and wetlands, as well as the production of perennial timber and biomass crops. Deforestation and degradation of forest ecosystems are responsible for about 1/8 of anthropogenic greenhouse gas emissions today (IPCC, 2014). Land use solutions reduce emissions from deforestation and degradation of ecosystems. Some protected ecosystems (e.g. coastal wetlands) continue to sequester carbon, while forest restoration and timber and biomass crops sequester significant amounts of carbon. Forests, peatlands, and coastal wetlands provide critical ecosystem services as well, while timber and biomass crops produce important feedstocks for construction, paper, energy, and other uses.
Coastal wetlands – the legal protection of carbon-rich mangroves, seagrasses, and saltmarshes, leading to reduced degradation rates and the safeguarding of carbon sinks.
Forest protection – the legal protection of forest land, leading to reduced deforestation rates and the safeguarding of carbon sinks.
Indigenous people’s land management – the legal recognition of forest tenure to indigenous peoples’ communities with claims to the land, leading to reduced degradation rates and the safeguarding of carbon sinks.
Peatlands – the protection of carbon-rich peatlands, leading to reduced degradation rates and the safeguarding of carbon sinks.
Temperate forests – the restoration and protection of temperate-climate forests, resulting in ongoing biosequestration.
Tropical forests – the restoration and protection of tropical-climate forests, resulting in ongoing biosequestration.
Afforestation – the planting of trees for timber or other biomass uses on degraded land, with biosequestration impacts in soil and biomass, and long-lived products across periods of cultivation.
Bamboo – the planting of bamboo for timber and other biomass uses on degraded land, with biosequestration impacts in soil, biomass, and long-lived products across periods of cultivation.
Perennial biomass – the production of perennial grasses and coppiced woody plants for bioenergy feedstock, resulting in net carbon in soils through biosequestration.
Each solution in the Land Use Sector was modeled individually, and then integration was performed to ensure consistency across the sector and with the other sectors.Information gathered and data collected are used to develop solution-specific models that evaluate the potential financial and emission-reduction impacts of each solution when adopted globally from 2020-2050. Models compare a Reference Scenario, that assumes current adoption remains at a constant percent of the current total land area, with high adoption scenarios assuming a reasonably vigorous global adoption path. In doing so, the results reflect the full impact of the solution, i.e. the total 30-year impact of adoption when scaled beyond the solution’s current status.
Land Use and supply-side Food Sector models define the Total Land Area as the area of land (in hectares) suitable for adoption by solutions. Data on global land is acquired from Global Agro-Ecological Zones database, developed by the Food and Agriculture Organization of the United Nations (FAO) and the International Institute for Applied Systems Analysis (IIASA). The Drawdown Land Use Model categorizes and allocates land according to agro-ecological zones based on the following factors: thermal climate, moisture regimes, soil quality, slope, cover type, and degradation status. These characteristics influence the suitability of different practices, and solution adoption scenarios are restricted by one or more of these factors.
Three general Project Drawdown scenario were developed for the Land Use Sector:
Each solution model uses unique adoption trajectories evaluated based on meta-analyses of existing prognostications of solutions, extrapolations from historical data, or scenario analyses depending on the availability of global and regional data.
Drawdown’s approach seeks to model integration between and within sectors, and avoid double counting. Several tools were developed to assist in this effort. The Agro-Ecological Zone (AEZ) model categorizes the world’s land by: current cover (e.g. forest, grassland, cropland), thermal climate, moisture regime, soil quality, slope, and state of degradation. Both Food (supply-side) and Land Use solutions were assigned to AEZs based on suitability. Once current solution adoption was allocated for each zone (e.g. semi-arid cropland of minimal slopes), zone priorities were generated and available land was allocated for new adoption. Priorities were determined based on an evaluation of suitability, consideration of social and ecological co-benefits, mitigation impact, yield impact, etc. For example, Indigenous Peoples’ land management is given a higher priority than forest protection for AEZs with forest cover, in recognition of indigenous peoples’ rights and livelihoods. Multistrata agroforestry is highly prioritized in tropical humid climates due to its high sequestration rate, food production, and highly limited climate constraints.
Each unit of land was allocated to a separate solution to avoid overlap between practices. The exception to this are farmland irrigation, nutrient management, and women smallholders, which can be implemented in addition to other practices. The constraint of limited available land meant that many solutions could not reach their technical adoption potential. The AEZ model thus prevents double-counting for adoption of agricultural and land use solutions.
Biosequestration does not have limitless potential. In most cases, there is a maximum amount of carbon that can be stored in soils and aboveground perennial biomass before they become saturated. Biosequestration continues after saturation but is offset by more or less equal emissions. In most cases, soils and biomass can return to their approximate pre-agricultural or pre-degradation levels of carbon. This takes anywhere between 10-50 years in agricultural cases, and sometimes longer in the case of ecosystems like forests. Data about saturation time is very limited.
The Drawdown land model takes the conservative approach that all land units currently adopted for land use like forest protection or afforestation have already achieved saturation, and will not be contributing additional sequestration. New adopted land is assumed to sequester for at least 30 years before achieving saturation.
Note that there are some important exceptions to saturation. Certain ecosystems continue to sequester soil carbon for centuries, notably peatlands and coastal wetlands. Some scientists argue that tropical forests can continue to sequester carbon at a slower rate after saturation. The addition of biochar to saturated soils may be able to overcome this constraint, as does the use of biomass from bamboo or afforestation in long-term products like buildings.
In Drawdown’s Plausible Scenario, Land Use Sector solutions are responsible for 14.2 percent of total emissions mitigation impact. In the Drawdown and Optimum Scenarios, they contribute 16.4 percent and 17.5 percent, respectively.
© 2017 Project Drawdown
Solutions in this sector include ecosystem protection, ecosystem restoration, and timber and biomass crops. Within this sector, ecosystem restoration solutions have the greatest mitigation impact, accounting for 55.9 percent, 54.2 percent, and 52.4 percent in the Plausible, Drawdown, and Optimum Scenarios, respectively. Ecosystem protection solutions account for 25.0 percent, 23.8 percent, and 21.0 percent, respectively (though the total stock protected is much higher, see Table 7). Timber and biomass crop solutions account for 19.1 percent, 21.8 percent, and 26.5 percent of mitigation impact, respectively.
© 2017 Project Drawdown
|Total Atmospheric Greenhouse Gas Reduction (in Gigatons)|
|Plausible Scenario||Drawdown Scenario||Optimum Scenario|
|Indigenous peoples' land management||6.19||8.16||5.19|
© 2017 Project Drawdown
Per-hectare impacts were calculated using meta-analysis. Tables 2 and 3 show the ranges, which were determined based on one standard deviation above and below the mean of all data collected. Sequestration types include soil organic carbon (SOC), aboveground biomass (AGB), or both. Emissions reduction includes carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).
|Land Use Sector Solution||Data Range||Model Input||Sequestration Type|
|Low||High||SOC or AGB|
|Coastal wetlands – mangroves||1.13||2.29||1.71||both|
|Coastal wetlands – saltmarshes||0.86||2.75||1.81||both|
|Coastal wetlands – seagrasses||0.49||1.71||1.10||both|
|Indigenous People's land management||N/A||N/A||0.60||both|
|Temperate forests (restoration)||1.29||4.64||2.96||both|
|Tropical forests (restoration)||2.15||4.61||3.38||AGB plus roots|
© 2017 Project Drawdown
Note: Bamboo sequestration rates include carbon stored in long-lived bamboo products.
|Land Use Sector Solution||Data Range||Model Input||Greenhouse Gas Type|
|Low||High||CO2, CH4, or N2O|
|Coastal wetlands – mangroves||-5.69||68.33||31.32||CO2|
|Coastal wetlands – saltmarshes||2.14||9.66||5.90||CO2|
|Coastal wetlands – seagrasses||7.71||12.00||9.85||CO2|
|Forest protection (one time)||173.07||454.51||313.79||all|
|Indigenous People’s land management||173.07||454.51||313.79||all|
© 2017 Project Drawdown
Ecosystem protection solution models are based on the reduction of historic degradation rates. Table 4 shows a range of degradation rates of unprotected ecosystems, determined based on one standard deviation above and below the mean of all data collected, along with the input selected for the model.
|Land Use Sector Solution||Data Range||Model Input|
|Coastal wetlands – mangroves||0.46||2.03||1.24|
|Coastal wetlands – saltmarshes||1.00||2.00||1.50|
|Coastal wetlands – seagrasses||0.91||5.91||3.41|
|Forest protection (one time)||0.07||0.31[i]||0.31|
|Indigenous People’s land management||0.02||0.04||0.03|
© 2017 Project Drawdown
Ecosystem protection solutions also serve as carbon stocks. Preserving these large carbon reserves is of critical importance to climate mitigation. Table 5 shows the total protected carbon stocks under the Plausible, Drawdown, and Optimal Scenarios.
|Coastal wetlands (combined)||14.6||15.9||16.8|
|Indigenous People’s land management||231.8||265.6||274.0|
© 2017 Project Drawdown
Financial impacts are not modeled for ecosystem restoration and protection solutions, as costs are highly variable and not necessarily borne by the land holder. Timber and biomass crop solutions offer substantial financial savings.
|Net Cost||Net Savings|
|Indigenous Peoples’ land management||$0||$0|
© 2017 Project Drawdown
[i] The weighted average degradation rate was calculated using the country level data on total forest area and rate of deforestation available for 1990-2015 (FAO, 2015).
[ii] The annual rate of peatland degradation is estimated based on the difference in the peatland area reported for the year 1990 and 2008 by the Wetland International.
The Intergovernmental Panel on Climate Change (IPCC) estimates that the potential for greenhouse gas emissions from global forestry of all types is 0.0-1.4, 0.1-9.5, and 0.2-13.8 gigatons. This estimate is based on prices of $20, $50, and $100 per ton of carbon dioxide emitted in 2030. Drawdown’s Plausible, Drawdown, and Optimum Scenarios for ecological protection and restoration solutions (representing comparably similar levels of adoption) achieve 5.9, 8.3, and 8.7 gigatons of reductions per year by 2050, respectively. This is well within the IPCC benchmark.
As for the timber and biomass crop solutions, the IPCC provides a benchmark of 4.0 gigatons of emissions per year in 2030 from afforestation, given a price of $100 per ton of emitted carbon dioxide per year (Climate Change 2007: Mitigation of Climate Change, Table 9.3). Drawdown’s three comparable solutions (afforestation, bamboo, and perennial biomass) achieve a combined impact of 0.5, 0.9, and 1.5 gigatons of emissions per year in 2030 in the three scenarios, respectively. Drawdown’s prioritization of food production and ecosystem restoration over afforestation is a possible reason for results lower than IPCC’s benchmark.
Improvements to land use are critical for climate change mitigation. Ecosystem protection solutions prevent loss of carbon currently held in forests and wetlands. Ecosystem restoration solutions and perennial timber and biomass have impressive biosequestration potential. Ecosystem protection and restoration offer essential co-benefits of ecosystem services, while perennial timber and biomass produce important products. Solutions in the Land Use Sector offer biosequestration as well as emissions reduction – and a livable climate cannot be attained without removal of excess atmospheric carbon.
Disturbance rates show the expected loss of protected and replanted forests and other ecosystems due to disturbances like fire. The model is built to include disturbance rates, but sufficient data was unavailable. This may be added to the model in the future as it becomes available. Restoration of peatlands and coastal wetlands was not modeled due to lack of data, though this is clearly desirable alongside protection. Albedo impacts are not modeled but would be useful to include in future upgrades.
How can you be sure that you didn’t double-count by allocating more than one solution to the same land? How did you divide up the world's land to these various solutions?
Our Agro-Ecological Zone Model divides the world's land by climate, soil fertility, degradation status, and slope. We first allocated the current adoption of all agricultural and land management solutions. Then we developed a list of priorities for each land type, and allocated solutions to land units using those priorities. Many solutions were unable to reach their theoretical adoption potential due to the limited space available. Thus, we avoided double-counting and generated a more realistic scenario than a single-solution approach might offer.
I don't see my favorite solution. Is there a list of other solutions that you considered, and why they did not make the cut? Is there a place to propose additional solutions?
Did you model the future impacts of climate change on land solutions?
We did not model the impacts of climate change on agriculture or ecosystems. While, in terms of impacts on agriculture, there will clearly be winners (mostly at high latitudes) and losers (particularly in the tropics), it is very challenging to model these impacts. Thus, our solutions model a "business as usual" climate.
How close does the scenario in the book come to the technical maximum for sequestration?
Rattan Lal reports the maximum global technical potential for sequestration in soils and biomass at 320 gigatons of carbon, or 1,174 gigatons of carbon dioxide. This maximum could only be reached if all ecosystems were somehow restored to their pre-anthropogenic state, with no houses, farms, or parking lots remaining. Drawdown's Plausible Scenario sequesters 84.4 gigatons of carbon, or 309.6 of carbon dioxide. So while it is an impressive impact, it represents only 26.5 percent of the theoretical maximum. Even our Optimum Scenario attains only about 42 percent of the theoretical maximum.
Isn’t carbon in biomass like trees highly vulnerable to being lost though fire, deforestation, etc.? Isn’t soil a more secure storage?
According to the IPCC, both soil and biomass (like the wood of trees) are both temporary and reversible though natural disaster and/or changes in management. Trees can be cut down or burned, while soils can be returned to tillage or badly-managed grazing. Drawdown advocates aggressive sequestration in both soils and perennial biomass.
Do your financials include payments for ecosystem services?
No, our financials no not include payments for ecosystem services (nor do they include a price on carbon).
Why no financials for some of the protection solutions?
It is assumed that any costs (e.g. carbon payments or payment for ecosystem services) are borne at a government or policy level. Drawdown land solutions only model costs that are incurred at the landowner or manager level.
What's the difference between reduction and protection?
Protection refers to the total amount of carbon stored in soil and biomass in ecosystems that is safeguarded by the solution. Reduction refers to the much smaller amount that would have been released to the atmosphere due to human activity (based on the current rate of destruction) if protection had not been put in place.
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