image: Land carbon sink in China at 2060 under a close-to-neutral emission scenario and the contributions of different anthropogenic inventions to land carbon sink (courtesy of Dr. Xu Yue)
Credit: Dr. Xu Yue
Many nature-based solutions have been proposed to farm the ecosystem for increased carbon uptake. Among those solutions, forestation (including afforestation and reforestation) has shown the largest potential and has been found to be responsible for large-scale greening and strengthened carbon sinks in China. However, considering the water and nutrient constraints on forest expansion, it is necessary to explore alternative solutions.
Here, researchers assess the potential of two alternative methods, ozone (O3) control and litter removal, in strengthening the land carbon sink in China. Surface O3 is an air pollutant that weakens plant photosynthesis due to its strong oxidizing capacity. Previous studies have shown the large benefits of O3 mitigation on the recovery of ecosystem productivity but have not yet quantified the possible gains in regional carbon sinks. Aboveground litterfall is composed of dead leaves, twigs, bark and so on. This debris typically decomposes within 1-3 years, leading to an increase in soil organic carbon (SOC) and heterotrophic respiration. Although litter removal might have negative impacts on SOC accumulation, field experiments reported that it helped reduce the carbon loss of the whole ecosystem through decreasing soil respiration.
In this study, researchers applied the state-of-the-art Yale Interactive terrestrial Biosphere (YIBs) model to project future changes in the land carbon sink in China at 2060. They used a recently updated land cover change (LCC) dataset that well captured the trend of forest area in China and extended it to 2100 with assumptions of fast, medium, and slow forestation rates for the future projection of carbon sink. They performed a total of 1152 simulations, each of which was run for 250 years driven with meteorological forcings from one of 16 climate models of the Coupled Model Intercomparison Project phase 6 (CMIP6) under 4 Shared Socioeconomic Pathways (SSPs) in 18 groups of varied configurations. They compared the potentials of strengthening land carbon sinks through forestation, O3 reduction, and litter removal in China.
At present day, the YIBs model predicted a sink of 0.48 Pg C a-1 at present with the updated LCC. Without anthropogenic interventions, the land carbon sink in 2060 is projected to be 0.23 Pg C a-1 under a close-to-neutral emission scenario SSP1-2.6. The major cause of reduced carbon sink is the weakened CO2 fertilization in this green scenario. With anthropogenic interventions, the national carbon sink becomes 0.47-0.57 Pg C a-1 at 2060, including the contributions of 0.12 Pg C a-1 by conservative forestation, 0.07 Pg C a-1 by ozone pollution control, and 0.06-0.16 Pg C a-1 by 20% litter removal over planted forest. This sink can mitigate 90%-110% of the residue anthropogenic carbon emissions at 2060.
With over 70 countries’ net-zero pledges by 2050-2070, recent projections showed that the temperature rise in the 2100s can be limited to below 2ºC above the preindustrial level, very similar to the warming pathway assumed by the SSP1-2.6 scenario. However, even for such a green scenario, the net carbon emission is not zero. To achieve carbon neutrality, negative emissions are required in addition to the improved efficiencies and renewables development. Our study shows that anthropogenic interventions to the ecosystems can act as an important measure of negative emissions by strengthening land carbon sinks in China, providing a solid foundation for the national carbon neutrality.
Journal
Science Bulletin