Widespread "greening paradox" of global forests: Increased greenness but higher climate change risks

Global forests have exhibited widespread greening trends over the past two decades, which are commonly recognized as positive signals of ecosystem restoration and enhanced carbon sequestration. However, how climate vulnerability evolved under widespread greening has not yet been assessed for global forests. To address this gap, this study investigated variations of climate change risks along greening gradient for global forests in 2003-2020 by applying the Vegetation Sensitivity Index (VSI) to three satellite-derived LAI products and FLUXNET ground observations. The climate change risk here refers to ecological vulnerability quantified by a composite metric that combines the VSI magnitude and its temporal trend. Our results indicated that more than 70% of global forests experienced greening in 2003-2020. While VSI magnitude generally decreased from tropical to cold-region forests, its temporal trends were positive in cold-region forests and negative in tropical forests, with temperate forests showing small net change. Crucially, we found that climate change risks increased progressively along the greening gradient, highlighting a widespread "greening paradox" in global forests. This paradox was most pronounced in tropical forests. The manifestation of this paradox was primarily associated with temperature and precipitation in tropical forests, with temperature in temperate forests, and with temperature and solar radiation in cold-region forests. Our study identifies a widespread co-occurrence between forest greening and heightened climate change risks, underscoring the need for forests management and adaptation strategies that account for this greening paradox under intensifying climate changes.