Increasing Extreme Thermal Events Threaten Marine Species

Global warming is causing frequent extreme thermal events that threaten marine species. However, accurately assessing their exposure remains challenging. Here, we utilize high-resolution daily ocean temperature data from 1950 to 2100 to identify extreme temperature events and quantify future exposure to extreme thermal conditions for 10,337 species, including marine mammals, coral reef organisms, and fish. Under the high-emissions scenario (SSP5-8.5), the annual growth rates of the extreme thermal index for these three groups are approximately 6 times greater than those under the low-emissions scenario (SSP1-2.6). Coral reef organisms exhibit the most rapid increase, with increase rates that are 1.68 and 1.04 times greater than those of mammals and fish, respectively─a pattern influenced by their limited mobility. Elevated extreme thermal exposure occurs for marine mammals and fish in semienclosed seas and polar waters. By the late 21st century, if high emissions persist, more than 60% of endangered species will experience extreme thermal exposure across more than half of their habitat ranges. These findings highlight the urgent need for transnational marine protected areas and stringent emission controls to mitigate impacts on marine biodiversity.