An empirical approach toward the SLCP reduction targets in Asia for the mid-term climate change mitigation

Abstract Although importance of co-control of SLCPs together with the emission reduction of CO2 has attracted much attention for the mid-term climate change mitigation, the contribution to radiative forcing (RF) is rather complex, and chemistry-climate model analysis for the future scenario tends to give a “black box” for the contribution of each species. In order to deliver a more straightforward message on the effect of the reduction of SLCPs to policymakers, we propose “top-down” reduction targets of CH4 and tropospheric O3 in reference to the historical levels of their RF. Although the RF increase due to the increasing CO2 concentration is inevitable in mid-term future (ca. 0.80 W m−2 in 2040), the RF of CH4 and O3 is expected to decrease from 0.48 to 0.41, 0.34, 0.27, and 0.22 W m−2, and from 0.40 to 0.29, 0.23, 0.19, and 0.15 W m−2, respectively, if their atmospheric concentrations decrease from the level of 2010 to those of 1980, 1970, 1960, and 1950, according to the IPCC 2013 database. Consequently, the sum of ΔRF x (CH4) and ΔRF x (O3) (the difference of RF between the target year of x and 2010 as the base year) are 0.18, 0.31, 0.42, and 0.51 W m−2 in 1980, 1970, 1960, and 1950, indicating that the increase of ΔRF2040(CO2) can be compensated by 23, 39, 53, and 64%, respectively. The policy target can be selected from the combination of different target years each for CH4 and O3. With this global reduction ratio, the necessary reductions in CH4, NO x , and NMVOC in Asia were estimated and compared with the GAINS model-based cost-beneficial reduction amount proposed by the Solution Report prepared under UN Environment Asia and the Pacific Office. In order to attain the targeted reduced emission level of CH4 and NO x , new technology/practice for the reduction of livestock emission of CH4 and energy transformation from fossil fuel to renewable energy is highly advantageous for NO x reduction from industrial/power plant sources.