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Empirical in-situ measurements of ecosystem carbon dioxide respiration (Reco) in high-latitude ecosystems remain limited, yet they are essential for understanding how tundra carbon cycling responds to climate warming across different environmental contexts and for reducing uncertainties in upscaled carbon budgets and carbon–climate feedbacks. Here, we present the TundraFlux Database, which to date is the most comprehensive synthesis of tundra Reco responses to experimental warming. The database compiles over 24 000 daily-aggregated in-situ Reco measurements from control and warmed plots with open-top chambers at 64 Arctic and alpine tundra sites across 12 countries. By coupling Reco measurements with extensive metadata on climate, vegetation, and soil characteristics, the TundraFlux Database enables the integration of field-scale ecological processes into large-scale models, offering new opportunities to refine global carbon budgets and test predictions of tundra ecosystem responses to warming. Open access to the TundraFlux Database will empower the research community to better quantify and predict how warming alters carbon cycling in Arctic and alpine tundra ecosystems. The data can be accessed on Zenodo (https://doi.org/10.5281/zenodo.17976235, Schwieger, 2026a).

Arctic and alpine tundra ecosystems are large reservoirs of organic carbon^1,2. Climate warming may stimulate ecosystem respiration and release carbon into the atmosphere^3,4. The magnitude and persistency of this stimulation and the environmental mechanisms that drive its variation remain uncertain^5–7. This hampers the accuracy of global land carbon–climate feedback projections^7,8. Here we synthesize 136 datasets from 56 open-top chamber in situ warming experiments located at 28 arctic and alpine tundra sites which have been running for less than 1 year up to 25 years. We show that a mean rise of 1.4 °C [confidence interval (CI) 0.9–2.0 °C] in air and 0.4 °C [CI 0.2–0.7 °C] in soil temperature results in an increase in growing season ecosystem respiration by 30% [CI 22–38%] (n = 136). Our findings indicate that the stimulation of ecosystem respiration was due to increases in both plant-related and microbial respiration (n = 9) and continued for at least 25 years (n = 136). The magnitude of the warming effects on respiration was driven by variation in warming-induced changes in local soil conditions, that is, changes in total nitrogen concentration and pH and by context-dependent spatial variation in these conditions, in particular total nitrogen concentration and the carbon:nitrogen ratio. Tundra sites with stronger nitrogen limitations and sites in which warming had stimulated plant and microbial nutrient turnover seemed particularly sensitive in their respiration response to warming. The results highlight the importance of local soil conditions and warming-induced changes therein for future climatic impacts on respiration.