Stronger response of vegetation photosynthesis to climate change than greenness in pan-Arctic region: First evidence from SIF satellite observations

The pan-Arctic terrestrial ecosystems are highly vulnerable to climate change. However, critical uncertainties remain regarding the relationship between vegetation photosynthesis and greenness and their climate sensitivities under accelerating climate change. Here, we conducted the first investigation of their climate responses by synergistically analyzing solar-induced chlorophyll fluorescence (SIF), a direct indicator of photosynthesis from the GOME-2A satellite, and normalized difference vegetation index (NDVI) from MODIS observations during the summers of 2007–2021. Our results demonstrate that both photosynthesis and greenness exhibited increasing trends, where 70.05 % of the vegetation pixels showed a consistent change, but with significant differences in growth magnitudes. Specifically, the growth magnitudes of SIF and NDVI were 6.09 % and 3.31 %, respectively, with the increase in SIF being approximately twice that of NDVI. Mechanistically, the accelerated rise in atmospheric CO₂ concentration (Δ33.27 ppm), and climate warming jointly enhanced the apparent SIFyield by 4.82 %, thereby directly amplifying SIF's stronger climate sensitivity. Structural equation modeling further quantified this disparity, revealing that SIF responded to climatic factors about 1.5 times stronger than NDVI. This study provides the first evidence from satellite SIF observations that vegetation photosynthesis exhibits larger growth magnitudes and more vigorous responses to climate change than greenness in pan-Arctic ecosystems, suggesting a new perspective on the traditional NDVI-centered framework in climate impact assessment. By integrating vegetation structural and functional dynamics, our findings provide critical physiological benchmarks to refine carbon-climate feedback projections.