| Popis: |
Reforestation is widely proposed for carbon dioxide (CO2) removal but the impact on climate, via atmospheric composition and surface albedo changes, remains relatively unexplored. Using two Earth System models, UKESM1 and CESM2, we compare scenarios where existing forests expand to a near biophysical limit (with croplands fixed at 2015 to preserve food production) with SSP1-2.6 and SSP3-7.0 at 2050 and 2095. In the reforestation scenario, global BVOC emissions are 18% (35%) higher than SSP3-7.0 at 2050 (2095) and 8% (12%) higher than SSP1-2.6. The resulting increases to secondary organic aerosols and aerosol scattering, from BVOC emission changes, drive a negative radiative forcing (RF). However, this is outweighed by the positive RF from increases to methane and ozone and decreases to surface albedo.The net RF is equivalent to CO2 increases of 13 (32) ppm relative to SSP3-7.0 at 2050 (2095) and 3 (8) ppm relative to SSP1-2.6. These indirect factors offset ~25% of the additional CO2 removal arising from reforestation relative to SSP3-7.0 and ~10% relative to SSP1-2.6. This highlights the importance of assessing the full response of the Earth System to reforestation, rather than just the potential CO2 removal. |
