What is United States's pathway to limit global warming to 1.5°C?
LULUCF
LULUCF emissions profile trajectories
The land use, land use change and forestry (LULUCF) sector in the United States absorbs more emissions than it generates, meaning it is a net sink. In 2020, forests and land removed a net –759 MtCO₂e out of the atmosphere which is equivalent to 13% of total emissions from other sectors in the US.1
According to the country’s national inventory, the largest net sources of LULUCF emissions are urbanisation (78 MtCO₂e/year) and land converted to cropland (54 MtCO₂e/year). Forests remaining forests are the largest emissions sink, sequestering a net –642 MtCO₂e/year in 2020. However, the LULUCF sink has declined by 16% since 1990, due to wood harvesting, ageing forests, and natural disturbances (see “Forest area change”).2
In the 1.5°C compatible pathway that we analysed, the LULUCF sector in the US continues to be net sink, with removals from afforestation / reforestation growing over time.
Making a direct comparison between this pathway and the government’s inventory data is not straightforward. The US government currently reports a much larger net sink in the LULUCF sector than the 1.5°C pathway because the inventory covers all carbon removals on managed land (which covers around 97% of US land), including sustainable forest management, net carbon accumulation in harvested wood products, and carbon sequestration from agricultural soils.3 Removals modelled in the 1.5°C pathway are limited to those from afforestation/reforestation. Some of the removals reported by the US government are not classified as anthropogenic by the model used to generate our pathway.4,5
In the 1.5°C pathway, sequestration from forest expansion increases to –375 MtCO₂/year by 2030, and over –1000 MtCO₂/year by 2050. In the long term, the sequestration rate declines as managed forests reach an equilibrium state.
The US Long-Term Strategy (LTS) projects that LULUCF net sequestration could reach about –700 to –1000 MtCO₂e/year by 2030 and about –600 to –1300 MtCO₂e/year by 2050 under the National Climate Strategy Action scenario. This is higher than our 1.5°C pathway because of the differences in coverage outlined above, and because this scenario includes some activities (e.g. restoring agricultural soils, among others) that are not accounted for in the 1.5°C pathway.6
When taken alongside the 1.5°C pathways excluding LULUCF, the sequestration implied in both this LULUCF 1.5°C pathway and the US’ long-term strategy would, if realised, allow net zero GHG emissions to be achieved by the early 2040s.
It is important to note that there is an inconsistency between modelled LULUCF emissions and removals and historical emissions and removals reported by countries. This is because of a difference in how anthropogenic emissions and removals are estimated in greenhouse gas inventories compared to models.7
United States' LULUCF emissions
MtCO₂/yr
Note that there is an inconsistency between modelled LULUCF emissions and sequestration and historical emissions and sequestration reported by countries. This is because of a difference in how anthropogenic emissions and sequestration are estimated in greenhouse gas inventories compared to models.
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Graph description
Historical CO2 emissions in 2005 – 2020 for the LULUCF sector are derived from national greenhouse gas inventories (data source: FAO 2021). Future emissions trajectory in 2025 - 2060 for the LULUCF sector is derived from a global 1.5°C compatible pathway downscaled to the country level (data source: IMAGE 2021). Positive emissions indicate an increase in deforestation or other sources related to land use change. Negative emissions indicate an increase of forest area through afforestation/reforestation.
Methodology
Data References
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United States' Forest area change
Million ha / yr
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Graph description
The graph indicates the annual rate of forest area change. Negative values result from a loss in forest area through deforestation and forestry (i.e. harvesting). Positive values result in forest area expansion through reforestation or afforestation. Data source: IMAGE 2021
Methodology
Data References
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Forest area change
After forests, the next largest land cover category in the US is pasture, accounting for over one-quarter of managed land. Other natural areas, such as wetlands and non-pasture grasslands, and croplands also account for a significant share of US land area. Grasslands in the US, including pastures, are a net source of emissions, largely owing to changes in mineral and organic soil carbon stocks.
Under the 1.5°C pathway analysed here, the US’ forested area increases by about 52 Mha in 2020–2030 and by 134 Mha in 2020–2050 through reforestation on abandoned pasture and cropland. The analysed pathway shows a 55 Mha decrease in pastureland in the US in 2020–2030 and 137 Mha in 2020–2050, which is high compared to other studies.8 Cropland also decreases, but to a lesser extent. While some abandoned pasture and cropland are populated by forests, some areas where trees fail to grow due to annual variability in temperature and precipitation are left abandoned.9
The 1.5°C pathway assumes reduced animal product consumption and food losses, and an increased yield in crop and animal products through technological advancement. Less consumption of meat and dairy products and more efficient agricultural practices lead to lower demand for agriculture expansion. Therefore, lifestyle changes and technological investment seem to be key drivers of abandonment of cropland and pasture that become available for reforestation.10
United States' Land cover areas
Million ha
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Graph description
The graph at the left shows the changes in land-use types relative to the total of available land in 2005 - 2060. The graph at the right shows the changes in land-use types relative to their 2020 levels. The land-use types included in the analysis are forest, land dedicated to pasture and cropland, built-up areas for settlements, and other natural area. This latter variable includes all areas unsuitable for agriculture, abandoned agricultural land, and natural forests. Data source: IMAGE 2021
Methodology
Data References
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United States' land cover change relative to 2020
Million ha
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Graph description
The graph at the left shows the changes in land-use types relative to the total of available land in 2005 - 2060. The graph at the right shows the changes in land-use types relative to their 2020 levels. The land-use types included in the analysis are forest, land dedicated to pasture and cropland, built-up areas for settlements, and other natural area. This latter variable includes all areas unsuitable for agriculture, abandoned agricultural land, and natural forests. Data source: IMAGE 2021
Methodology
Data References
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Evolution of land-use pattern
Forests make up 32% of land area in the US and have remained relatively constant in size with total forest area declining by less than 1% since 1990.11 The vast majority, about 97%, of forests in the US is considered managed land, primarily timberland.
Forestry is the dominant driver of tree cover loss in the US, followed by wildfires; land area burned by large wildfires has increased substantially since the 1980s, mostly impacting the Pacific Coast and Rocky Mountain regions.12 However, only about 6% of tree cover loss between 2001 and 2021 resulted in permanent deforestation.13 Permanent deforestation is primarily driven by urbanisation and commercial agriculture.
In the 1.5°C compatible pathway analysed here, reforestation and reducing deforestation are key activities for maintaining the net sink in the US’s LULUCF sector. Reforestation expands forested areas onto abandoned agricultural land.14 The pathway implies that reforestation at a rate of around 5 Mha/year can expand forest area by 51 Mha in 2020–2030, while safeguarding biodiversity and food production (see “Evolution of land use”). The years leading to 2050 show the highest annual rate of reforestation. After 2050, the rate of reforestation decreases as additional land is limited.
A recent assessment found that the US has nearly 60 Mha of potential land for reforestation. The assessment assumed that reforestation takes place in areas that were historically forests. It also considered on-the-ground feasibility of the modelled reforestation as well as safeguarding food production and biodiversity. The study concluded that reforestation in the US will require investments in seed procurement, workforce, and other components in forest management. To reach even half of this reforestation potential, the US would need to more than double the scale of the nation’s tree nursery sector.15 This implies that reforestation of up to 130 Mha during 2020 – 2050, as indicated in this pathway (see “Evolution of land use”), would likely face challenges and require scaled-up investments and effective safeguards. As part of the bipartisan Infrastructure Investment and Jobs Act, the REPLANT provision directs the US Forest Service to plant more than one billion trees over the next decade and increases available resources, such as funding to develop nurseries.16