Every tonne matters: marginal emission reductions have human-scale benefits

Mitigating climate change to reach international targets requires action by public and private actors on all scales. Yet, the effectiveness of emission reductions by individual people, organizations, regions, and countries is often perceived to be small, limiting both private and public mitigation efforts. Currently, there is no comprehensive quantification of the consequences of individual-scale emission reductions on relatable climate change outcomes. Here, we introduce and quantify the “one-tonne effect,” which measures the effect of each tonne of CO₂ emission reductions based on climate impact projections using a flexible statistical estimation framework. We apply this framework to 16 climate impacts across hydrology, cryosphere, ecosystems, food, and well-being. We show that the one-tonne effect is on human scales—comparable to everyday human dimensions and perceptions—for most impacts, given current expected warming. For systems at risk of complete loss, such as coral reefs, marginal emission reductions delay complete loss, with rapidly increasing effects under more ambitious climate policies. By demonstrating that each tonne of emission savings contributes meaningfully to reducing climate damages, our findings show that individual climate actions matter. Our estimates can be used to quantify the benefits of private and public mitigation efforts, and motivate individuals to reduce their emissions