Climate change is shifting the growing seasons of plants, affecting species performance and global biogeochemical cycles. Yet, how the timing of autumn leaf senescence in northern forests will change remains highly uncertain because of the complex seasonal effects of environmental drivers. Using experiments, ground observations, carbon flux measurements and satellite-derived monitoring, we show that early-season and late-season warming have opposite effects on leaf senescence, with a reversal occurring after the year's longest day (summer solstice). Across 84% of the northern forest area, increased temperature and vegetation activity before the solstice led to an earlier senescence onset (10% greenness loss) of, on average, –1.9 ± 0.1 days-per-°C, while warmer post-solstice temperatures increased senescence duration by +2.6 ± 0.1 days-per-°C. The current trajectories toward an earlier onset and slowed down progression of senescence reveal Northern Hemisphere-wide compensation effects on trends in growing-season length and forest productivity.