Forest residues contribute significantly to climate change in China.

• Forest residues, a renewable energy, have great potential to substitute fossil fuels to reduce enormous pressures of energy shortages in mitigating climate change. However, it is a challenge to quantify forest residues at a fine spatial scale due to large spatial variations of forest species and lacking of suitable research methods. In addition, the natural decomposition of forest residue is often ignored in future greenhouse emission prediction, • We estimated the total forest residues in China reached 152.13 million t in 2018. The forest residues had faster decomposition rate (annual natural decomposition value of carbon from forest residues) in the first ten years, and then gradually decreased. In the first 14 years, the half forest residues was decomposed. The national contribution to climate change (CCC) from forest residues over one-hundred-year reached 49.27 million t CO 2 eq. The peak values of the provincial annual CCC were reached within 15 years and we found that the highest annual CCC occurred in the second year since the natural decomposition. • There are two major contents. First, a method is put forward to downscale the reserve of forest residue to county-level administrative unit. Prior to this, the resolution of the estimations was generally at provincial level. Obviously, more refined data was conducive to encourage the utilization of biomass by providing references for policymakers and investors. Second, a new index was implemented to assess the contribution of the natural decomposition of unused forest residues to climate change. • We estimated that CCC caused by their natural decomposition reaches 4.927 million t CO 2 eq, which was 0.96%−6.5% of other carbon emission sources (i.e. staple crops, inland water) in China. From a global perspective, such carbon emission was 0.015% of global wetland carbon emissions and 1.59% of global peat land carbon emissions. • Our study provides new data to support future climate mitigation, reducing the significant uncertainty in related research, and will make researchers, policymakers, and investors recognize the great potential of forest residues as an energy source and the significant contribution of their natural decomposition to climate change and promote carbon neutrality transition. Under the energy shortage and emerging climate change caused by fossil energy, forest residues were encouraged to be used as an energy resource. However, it is a challenge to quantify the forest residue at the fine spatial scale due to the available data and suitable research methods. We aimed to quantify the available forest residues in China at the county scale and clarify their potential contribution to climate change (CCC). The availability of forest residues reached 152.13 million t in 2018 in China. The CCC accumulated by natural decomposition of forest residues over one-hundred-year had reached 49.27 million tCO 2 eq. The peak values of provincial annual CCC were reached in the first 3 years in the southern region. The top four counties of CCC were all from Yunnan Province. The energy utilization of forest residues is of great significance to the management of forest resources. [Display omitted] [ABSTRACT FROM AUTHOR]