We combine general circulation modeling (GCM), remote sensing, and field results to identify a positive feedback loop in which clearing of tropical savannas results in warmer and drier climate, accelerated fire frequencies, and further tree cover loss. The GCM simulations indicate that ongoing clearing of tropical savannas increases temperatures and wind speeds and decreases precipitation and relative humidity, substantially increasing fire frequency. Using NOAA-12 satellite images and meteorological data, we estimate that complete savanna clearing will increase fire frequency by 42%. Combining these data with long-term fire studies, we demonstrate that this fire-mediated feedback may already be contributing to declining tree densities in the world's savannas and will become increasingly important as vegetation change continues in the coming century.