LAUSR

Understanding the changes in marine heatwaves (MHWs) is vital for safeguarding marine ecosystems and effective risk management. However, previous studies have assumed stationary changes, leaving the dynamics of MHW properties within a non‐stationary framework unclear. Here, using an improved non‐stationary framework, we show that the 20‐, 50‐, and 100‐year MHWs have been substantially underestimated in most oceans. Approximately half of the world's oceans are now experiencing increasingly prolonged MHWs. On average, at the 100‐year return level, global MHWs have more than doubled in duration, while increasing by 67% in frequency and 23% in intensity. Further analysis reveals that increasing anthropogenic greenhouse gas emissions are the primary driver of observed changes, accounting for over 80% of the changes in MHWs. Our findings suggest that under greenhouse warming, MHWs are likely to become more frequent, intense, and persistent, with important implications for adaptation and mitigation strategies for MHWs.