The availability of carbon and nitrogen to ecosystems is increasing due to rising atmospheric CO2 levels and human-induced inputs, but phosphorus inputs are not increasing proportionally. This imbalance in the stoichiometry of carbon, nitrogen, and phosphorus has unprecedented implications for Earth's ecosystems. The authors use a mass balance approach to show that limited phosphorus and nitrogen availability will likely reduce future carbon storage by natural ecosystems. They also find that if phosphorus fertilizers become less accessible, crop yields in developing regions may decrease. The global demand for phosphorus is growing faster than the supply, leading to a nitrogen-to-phosphorus imbalance that may alter Earth's organisms and ecosystems. Excessive phosphorus fertilizer use in developed countries can cause eutrophication in downstream ecosystems, while developing countries lack sufficient phosphorus fertilizers, affecting food security. The increasing N:P ratio in the environment affects the metabolism and growth rates of organisms, altering community composition and ecosystem functioning. The authors conclude that the unbalanced human-induced inputs of carbon, nitrogen, and phosphorus are altering environmental N:P ratios, which are vital for controlling organism and ecosystem functioning, the carbon cycle, climate, and agriculture. However, the exact impacts of these changes on microbial, plant, and animal communities remain poorly understood.The availability of carbon and nitrogen to ecosystems is increasing due to rising atmospheric CO2 levels and human-induced inputs, but phosphorus inputs are not increasing proportionally. This imbalance in the stoichiometry of carbon, nitrogen, and phosphorus has unprecedented implications for Earth's ecosystems. The authors use a mass balance approach to show that limited phosphorus and nitrogen availability will likely reduce future carbon storage by natural ecosystems. They also find that if phosphorus fertilizers become less accessible, crop yields in developing regions may decrease. The global demand for phosphorus is growing faster than the supply, leading to a nitrogen-to-phosphorus imbalance that may alter Earth's organisms and ecosystems. Excessive phosphorus fertilizer use in developed countries can cause eutrophication in downstream ecosystems, while developing countries lack sufficient phosphorus fertilizers, affecting food security. The increasing N:P ratio in the environment affects the metabolism and growth rates of organisms, altering community composition and ecosystem functioning. The authors conclude that the unbalanced human-induced inputs of carbon, nitrogen, and phosphorus are altering environmental N:P ratios, which are vital for controlling organism and ecosystem functioning, the carbon cycle, climate, and agriculture. However, the exact impacts of these changes on microbial, plant, and animal communities remain poorly understood.