The global potential for increased storage of carbon on land

Abstract

Constraining the climate crisis requires urgent action to reduce anthropogenic emissions while simultaneously removing carbon dioxide from the atmosphere. Improved information about the maximum magnitude and spatial distribution of opportunities for additional land-based removals of CO2 is needed to guide on-the-ground decision-making about where to implement climate change mitigation strategies. Here, we present a globally consistent spatial dataset (approximately 500-m resolution) of current, potential, and unrealized potential carbon storage in woody plant biomass and soil organic matter. We also provide a framework for prioritizing actions related to the restoration, management, and maintenance of woody carbon stocks and associated soils. By comparing current to potential carbon storage, while excluding areas critical to food production and human habitation, we find 287 petagrams (PgC) of unrealized potential storage opportunity, of which 78% (224 PgC) is in biomass and 22% (63 PgC) is in soil. Improved management of existing forests may offer nearly three-fourths (206 PgC) of the total unrealized potential, with the majority (71%) concentrated in tropical ecosystems. However, climate change is a source of considerable uncertainty. While additional research is needed to understand the impact of natural disturbances and biophysical feedbacks, we project that the potential for additional carbon storage in woody biomass will increase (+17%) by 2050 despite projected decreases (−12%) in the tropics. Our results establish an absolute reference point and conceptual framework for national and jurisdictional prioritization of locations and actions to increase land-based carbon storage.

Keywords: forest maintenance; forest restoration; improved forest management; natural climate solutions; negative emissions.

Fig. 1.

The NCS opportunity space, consisting of seven categories defined by the ratio of current (x axis) to potential (y axis) carbon storage as well as carbon-based thresholds delineating NCS-relevant systems. Categories include: Restore/High suitability for forestry-based NCS (R/H; red), Maintain and manage/High suitability for forestry-based NCS (MM/H; dark green), Maintain/High suitability for forestry-based NCS (M/H; dark blue), Restore/Low suitability for forestry-based NCS (R/L; orange), Maintain and manage/Low suitability for forestry-based NCS (MM/L; light green), Maintain/Low suitability for forestry-based NCS (M/L; light blue), and Nonwoody (yellow). † denotes associated grassland/savanna biodiversity considerations.

Fig. 2.

The global distribution of NCS opportunities. (A) The geographic distribution of seven NCS opportunity categories. (B) The contribution of each opportunity category to unrealized potential carbon storage (PgC) among bioclimate zones and at the global scale. (C) The latitudinal distribution of unrealized potential carbon (PgC) storage in ABG, BGB, and SOC by opportunity category relative to A. Uncertainties reflect the AGB + BGB component only (see Table 1). All estimates are constrained to safeguard food production and human habitation.

Fig. 3.

Top 25 countries ranked in terms of total constrained unrealized potential carbon stored in biomass and soil. (A) The total opportunity by country across seven NCS opportunity categories, which accounts for almost 75% of the total constrained unrealized potential for additional land carbon (PgC) storage. (B) The total by country in A expressed per unit area of opportunity (i.e., opportunity density). (C–H) The opportunity density by country in A disaggregated among six opportunity categories: R/H, MM/H, M/H, R/L, MM/L, and M/L.

Fig. 4.

Projected risk of change in the unrealized potential carbon stored in ABG + BGB by 2050 due to climate change (RCP8.5). (A) Country-level map illustrating baseline (1960 to 1990) unrealized potential carbon storage (PgC) and change (%) relative to RCP8.5 (mean of 11 Earth system models). (B) Latitudinal distributions of unrealized potential carbon storage (PgC) assuming baseline climate (blue line) and future climate (yellow envelope; RCP8.5; range of 11 Earth system models). (C) Distribution of unrealized potential carbon density (MgC ha⁻¹) by bioclimate zone under baseline and future climate (RCP8.5; mean of 11 Earth system models). Insets truncate the y-axis range to 270 Mha. (D) Total unrealized potential carbon (PgC) storage by bioclimate zone and NCS opportunity category under current climate (colored horizontal bars) and future climate (black symbols representing RCP8.5; mean and range of 11 Earth system models). All estimates are constrained to safeguard food production and human habitation.

Fig. 5.

The opportunity for additional carbon storage in Brazil. (A) Carbon (PgC) stored in current and unrealized potential AGB, BGB, total biomass (AGB + BGB), SOC, and the sum of biomass and soil (AGB + BGB + SOC) in Brazil by NCS opportunity category. Estimates of unrealized potential carbon storage in total biomass (ABG + BGB) by 2050 due to climate change (RCP8.5; mean and range of 11 Earth system models) are also included. Maps depict the geographic distribution of (B) seven NCS opportunity categories and (C) unrealized potential carbon (MgC ha⁻¹) storage (assumes baseline climate). All estimates are constrained to safeguard food production and human habitation.