Land-use emissions play a critical role in land-based mitigation for Paris climate targets

Abstract

Scenarios that limit global warming to below 2 °C by 2100 assume significant land-use change to support large-scale carbon dioxide (CO₂) removal from the atmosphere by afforestation/reforestation, avoided deforestation, and Biomass Energy with Carbon Capture and Storage (BECCS). The more ambitious mitigation scenarios require even greater land area for mitigation and/or earlier adoption of CO₂ removal strategies. Here we show that additional land-use change to meet a 1.5 °C climate change target could result in net losses of carbon from the land. The effectiveness of BECCS strongly depends on several assumptions related to the choice of biomass, the fate of initial above ground biomass, and the fossil-fuel emissions offset in the energy system. Depending on these factors, carbon removed from the atmosphere through BECCS could easily be offset by losses due to land-use change. If BECCS involves replacing high-carbon content ecosystems with crops, then forest-based mitigation could be more efficient for atmospheric CO₂ removal than BECCS.

Fig. 1

Scenarios for land-use and climate change. a, b Land used for food production (crops and pasture) and bioenergy crops from the IMAGE SSP2 scenarios IM1.9 and IM2.6 (available from https://data.knmi.nl/datasets?q=PBL). c Temperature profiles for the idealized scenarios reaching nearly 1.5 °C and 2 °C by 2100. d CO₂ concentrations for each of the 34 ESMs emulated with IMOGEN. The CO₂ concentrations relate to the temperatures in c depending on each model’s climate sensitivity (Methods). e, f Spatial maps of change in land for bioenergy crops in IM1.9 and IM2.6. For each scenario, the change is shown as the difference between 2000 and the year of maximum extent of bioenergy crops (2060 for IM1.9 and 2085 for IM2.6)

Fig. 2

Carbon cycle responses to two land-use and two climate stabilization scenarios simulated by the land surface model JULES. Land-use scenarios are shown with different colours: IM1.9 (orange) and IM2.6 (purple), and the climate scenarios are shown with different line patterns: 1.5 °C (solid) and 2 °C (dashed) above preindustrial by 2100. Panels show simulated vegetation (a) and soil carbon (b), the cumulative storage of carbon through BECCS (c), and the total land carbon stock (including captured carbon via BECCS) (d). Shading shows ± 1 standard deviation from the ensemble mean from the 34 ESM climates represented in IMOGEN

Fig. 3

Simulated changes in soil and vegetation carbon due to land use and climate change. Carbon stored in soils (a, b) and vegetation (c, d) is simulated by the land surface model JULES. The changes are shown in kg m⁻² from 2000 to 2099 for the IM1.9 (a, c) and IM2.6 (b, d) land-use scenarios with the 1.5 °C climate change scenario

Fig. 4

Changes in tree and shrub coverage simulated by the land surface model JULES (units = fraction of grid cell). The changes are from 2000 to 2060 (a, b) and from 2060 to 2099 (c, d) for the two land-use scenarios with the 1.5 °C climate change scenario

Fig. 5

Attribution of differences in land carbon stocks between scenarios based on JULES model simulations. a The net difference (sum of C_veg + C_soil + geologically stored CO₂ from BECCS) and each component between 1.5 °C_IM1.9 and 2 °C_IM2.6. Positive values indicate larger land carbon stocks in 1.5 °C_IM1.9. b The drivers of the land use change effect. Total LUC effect (olive green in panel a) can be attributed to LUC for: food production (crop and pasture), BECCS, and land abandonment/reforestation. These are shown with the cumulative carbon removed via BECCS for comparison

Fig. 6

Comparison of forests and bioenergy crops with carbon capture and storage for carbon storage based on JULES simulations. a, b Change in forest carbon stocks over the 21st century (vegetation, soils and woody product pools) for the 1.5 °C climate scenario with IM1.9 and IM2.6 land use patterns. c, d Recovery time for BECCS. Blues indicate the recovery time is 0 years, and instead shows the mean annual flux of captured carbon via BECCS. e Difference in total carbon stocks (including accumulated storage via BECCS) at 2100 on grid cells where the two scenarios have conflicting land-use change. The convention is: scenario with bioenergy crops minus scenario with forests, such that blues indicate more carbon stored with BECCS and reds indicate more carbon stored with forests. f The percentage of points in e, in which BECCS is more successful at accumulating carbon than forest preservation or reforestation, showing the effect of increasing the default carbon storage from BECCS in JULES. Crosses indicate the benefit of harvesting initial aboveground biomass for BECCS as in IMAGE

Fig. 7

Comparison of bioenergy crop yields as simulated by JULES and IMAGE. Zonal mean non-woody potential biomass from IMAGE (black lines) ± 1 standard deviation (shading) in 2060 (a) and 2090 (b) with IM1.9 compared to JULES: solid line is the aboveground NPP, and the dashed line is the harvest on bioenergy crop tiles