Human-induced nitrogen-phosphorus imbalances are altering natural and managed ecosystems globally. The availability of carbon and nitrogen has increased, but phosphorus inputs have not kept pace, leading to a significant shift in the carbon-to-nitrogen-to-phosphorus (C:N:P) stoichiometry. This imbalance is likely to reduce future carbon storage by terrestrial ecosystems and increase nutrient deficits in developing regions. The global phosphorus fertilizer application is around 17 Tg P per year, while nitrogen fertilizer use has increased over 10 times since the 1950s. The N:P ratio of fertilizer inputs has increased by 51% since 1975, creating a growing gap in phosphorus access between developed and developing countries. Atmospheric nitrogen deposition is widespread, especially in northern ecosystems, while phosphorus deposition is limited to mineral aerosols. The N:P ratio of atmospheric deposits has increased in the Northern Hemisphere since pre-industrial times. Future projections suggest an expansion of high anthropogenic nitrogen deposition into tropical regions. The stoichiometry of these deposits is currently much higher than that of terrestrial plants and marine plankton. These imbalances are likely to alter the environment and the life it supports. Climate-carbon cycle models generally do not account for nutrient limitations, leading to overestimations of future carbon storage. Recent studies show that nutrient feedbacks can reduce productivity by up to 50% in the 21st century. The human imprint on the phosphorus cycle and N:P stoichiometry is likely to reduce future carbon storage by natural ecosystems and increase nutrient deficits in developing regions. The analysis of phosphorus and nitrogen demands for changes in land carbon stocks shows that phosphorus limitations will be met first, followed by nitrogen limitations. The global phosphorus pool is only 13.2 Pg P, and the extra amount needed to sustain increased carbon storage exceeds all plausible phosphorus supply scenarios by 2100. The projected depletion of mineable phosphorus reserves by 2100 highlights the urgency of addressing this imbalance. The study underscores the complex and uncertain impacts of N:P imbalances on ecosystems, carbon cycling, and climate.Human-induced nitrogen-phosphorus imbalances are altering natural and managed ecosystems globally. The availability of carbon and nitrogen has increased, but phosphorus inputs have not kept pace, leading to a significant shift in the carbon-to-nitrogen-to-phosphorus (C:N:P) stoichiometry. This imbalance is likely to reduce future carbon storage by terrestrial ecosystems and increase nutrient deficits in developing regions. The global phosphorus fertilizer application is around 17 Tg P per year, while nitrogen fertilizer use has increased over 10 times since the 1950s. The N:P ratio of fertilizer inputs has increased by 51% since 1975, creating a growing gap in phosphorus access between developed and developing countries. Atmospheric nitrogen deposition is widespread, especially in northern ecosystems, while phosphorus deposition is limited to mineral aerosols. The N:P ratio of atmospheric deposits has increased in the Northern Hemisphere since pre-industrial times. Future projections suggest an expansion of high anthropogenic nitrogen deposition into tropical regions. The stoichiometry of these deposits is currently much higher than that of terrestrial plants and marine plankton. These imbalances are likely to alter the environment and the life it supports. Climate-carbon cycle models generally do not account for nutrient limitations, leading to overestimations of future carbon storage. Recent studies show that nutrient feedbacks can reduce productivity by up to 50% in the 21st century. The human imprint on the phosphorus cycle and N:P stoichiometry is likely to reduce future carbon storage by natural ecosystems and increase nutrient deficits in developing regions. The analysis of phosphorus and nitrogen demands for changes in land carbon stocks shows that phosphorus limitations will be met first, followed by nitrogen limitations. The global phosphorus pool is only 13.2 Pg P, and the extra amount needed to sustain increased carbon storage exceeds all plausible phosphorus supply scenarios by 2100. The projected depletion of mineable phosphorus reserves by 2100 highlights the urgency of addressing this imbalance. The study underscores the complex and uncertain impacts of N:P imbalances on ecosystems, carbon cycling, and climate.