China's vegetation restoration programs accelerated vegetation greening on the Loess Plateau

•Climate change and restoration policies are the primary and secondary factors to the greening of the Loess Plateau.•The difference-in-differences method suggest lowered contribution of the restoration policy to vegetation greening than previously thought.•Using spatially specific starting time of the policy implementation instead of a fixed year can help better estimate the effects of restoration programs. The vegetation greening on the Loess Plateau, China, over recent decades, has been primarily driven by a series of vegetation restoration programs (VRPs) and other natural environmental changes (including climate change, rising atmospheric CO2 concentration, and nitrogen deposition, etc.). However, accurate determination of the contributions of natural environmental change and the VRPs to this greening has been challenging due to the lack of the exact time of policy implementation in different areas. Herein, we extracted the starting time of greening (SOG) from different sources of remote sensing data and used it as the starting time of the VRPs. Then, we employed a difference-in-differences (DID) method to ascertain the relative contributions of the VRPs on the observed vegetation greening. Results showed that the contribution of the VRPs to vegetation greening on the Loess Plateau was 23.8–35.8 %, with a greater contribution potentially originating from natural environmental factors. Our findings contribute to a better understanding of the complex relationships among vegetation restoration policies and climate change, and offer a platform to quantify the climate effects on vegetation greening.