This article explains the dynamics of greenhouse gas emissions and removals from land use, land use change, and forests in En-ROADS. Watch the video below for a summary.
Forest carbon removal capacity
En-ROADS shows the capacity of land to remove CO2 from the atmosphere under different scenarios of climate action. For example, the best way to see the results of less deforestation in En-ROADS is to look at the graphs: “CO2 Net Emissions from Land Use” (under Graphs > CO2 Emissions) and “CO2 Removals from Land” (under Graphs > CO2 Removals).
The scenario in the graphs above has the main Deforestation slider set to the maximum reduction rate. The “CO2 Net Emissions from Land Use” graph (on the left) shows the decline in net carbon dioxide emissions from reduced burning and rotting biomass due to less deforestation and the ongoing carbon removal of forests that are left intact. As forests are left to grow, they sequester carbon in plants and soils, so there is a boost in CO2 removals when deforestation is reduced (as seen in the graph “CO2 Removals from Land” on the right).
The key takeaway is:
Protecting forests not only avoids releasing locked-in carbon into the atmosphere, but it also increases the capacity of the land to remove additional carbon.
En-ROADS and C-ROADS account for forest degradation—the deterioration of forests due to natural disturbances and harvesting for wood products and bioenergy. Forest degradation occurs in forests of all ages, but in the simulators there is a particular focus on the degradation of mature forests (over 100 years old) because of the large amount of carbon that is stored in them. This carbon can be the source of significant emissions if the forests are degraded through harvesting.
The main Deforestation slider in En-ROADS and the inputs in C-ROADS reduce both deforestation (permanent forest loss) and mature forest degradation. There are also additional sliders in the En-ROADS Deforestation advanced view to limit these actions individually.
Mature forest degradation is a significant source of CO2 emissions since older forests have large accumulated stores of carbon that can be released and then take decades to reabsorb as forests regrow.
The shifts in forest age are best seen in the “Forest Area by Age” graph in En-ROADS (under Graphs > Land, Forestry, and Food).
In this scenario where the main Deforestation slider is set to the maximum rate of reduction, forests are allowed to grow older and mature forests (solid green line) form a larger share of total forest land relative to the Baseline (dashed green line). This means there is more carbon overall retained in plants and soils, and there are also widespread benefits to biodiversity, animal habitats, hydrological systems, and more.
Drivers of forest change
Deforestation is largely driven by demand for additional cropland. Urbanization and other factors play a much smaller role globally. The demand for cropland is driven by population, economic growth, and crop yield, but it is primarily shaped by the policies and choices that are made around food. Read more in the Explainer on Food and Agriculture in En-ROADS here.
The following sections provide more detailed context.
Context and background
Forests are natural carbon sinks, taking in CO2 from the atmosphere through photosynthesis and sequestering it long-term in plants and soils. As a result, protecting forests so that they maintain—or even increase—the carbon removal capacity of the land is a natural solution to reducing carbon dioxide in the atmosphere. However, given the scale of emissions from fossil fuels, forests can play only a limited role in addressing climate change by themselves.
Understanding the modeling and dynamics of forests
When trees are harvested, either to clear land, or to provide feedstocks for bioenergy, wood, or paper products, the carbon stored in the trees is eventually released to the atmosphere. En-ROADS adds these emissions into the carbon cycle based on differing rates of decay. Wood harvested for non-fuel products decays over a 30-year period, an estimate that accounts for long-lived construction and furniture products and short-lived paper products. Emissions from deforestation for farmland expansion and wood for bioenergy feedstocks are modeled as immediate emissions.
When moving the “Reduction in mature forest degradation” slider (under the Deforestation advanced view) to the maximum level, En-ROADS simulates a policy that preserves mature forests from human-caused degradation. The “Deforestation and Mature Forest Degradation” graph on the left below shows the decline in mature forest degradation, which eventually reaches zero. Although bioenergy and wood product harvesting has ceased in mature forests by 2050 in this scenario, the demand for bioenergy and wood products continues to be met by forests that are less than 100 years old. As a result, there continue to be emissions from forest degradation in the graph “CO2 Gross Emissions from Forests.”
Key En-ROADS Graphs
Key graphs related to forests and land use can be found under:
- Graphs > Land, Forestry, and Food
- Graphs > CO2 Emissions > Emissions from Land Use
- Graphs > CO2 Removals
The “Carbon in Forests” graph under Graphs > Land, Forestry, and Food (below), shows the stocks of carbon stored in plants and soils of forests. This graph illustrates the large stock of carbon stored in the soil of forests, which takes decades to re-accumulate after being released when forests are degraded.
The “Forest Area” graph (under Graphs > Land, Forestry, and Food) shows the area of land covered by forests. In En-ROADS, there are three primary types of land globally: forest, farmland, and other land. Actions, like shifts to plant-based diets, result in changes in land across these three types (e.g., more food production requires more farmland, which reduces forests and other land). Although shifts to forest land area may look small relative to the total area of forests, they have significant impacts on emissions and the ecosystems and communities that rely on forests.
Planting new trees via afforestation increases carbon dioxide removal but requires a significant area of land, as seen in the “Land for CO2 Removal” graph below. In En-ROADS, these new forests come from other land (e.g., wild grasslands). However, the reality of large-scale afforestation is that land is generally hard to secure for new purposes like growing trees and takes time to plant so it takes decades to scale-up (in En-ROADS the afforestation advanced sliders “Time to secure land for afforestation” and “Afforestation planting time” can be adjusted to explore these dynamics).
The “CO2 Removal from Afforestation” graph (below) shows the significant difference in how much total carbon dioxide is removed via afforestation and how much is removed on net after accounting for emissions. Forests are dynamic ecosystems that result in both carbon removals and emissions, with soils and other biomass continually cycling carbon in and out of the atmosphere regardless of the age of the trees in the forests. As forests mature, they become more likely to die, decay, or succumb to wildfires, which also result in a source of carbon dioxide emissions. This is seen below as the rate of net carbon dioxide removal levels off.