Likelihood of record breaking heat controlled by current record margin and spatial pattern of warming

The probability of record heat is increasing under climate warming; however, the factors controlling spatial and temporal variations in the probability of record breaking heat have not been systematically investigated. Here, we use large ensemble seasonal hindcast data for 1980-2024 to quantify how the probability of breaking records for the climatologically warmest month has evolved across different regions. We isolate the roles of the evolving record margin, background climate change, and climate variability in shaping the probability of breaking the current record. An observed record-breaking event reduces the likelihood of further records under a stationary climate, with larger record margins associated with larger decreases in record probability. Global warming has increased record probability; however, this effect varies significantly at regional scales with largest increases in Arabian Peninsula and smaller increases in Parts of Russia and Central Asia. El Nino events increase the probability of record warmth across the tropics by around 5% compared with during La Nina. The results demonstrate that the probability of record warm months is controlled by a combination of regional factors, including the evolution of existing records and externally forced warming, leading to a heterogenous distribution of current risk.