The results show that, globally, marine heatwaves have become 34% more likely and 17% longer between the early 20th century and the early 21st century. The study gathered SST data collected from coastlines, ships and satellites on daily and monthly timescales to create one record. It shows also that the number of days each year with a marine heatwave has increased by 54% since the early 20th century. Much of the recorded change has occurred over the past several decades, which suggests that the warming trend has accelerated. This trend in marine heatwaves can largely be explained by increases in mean ocean temperatures, suggesting that we can expect, further increases in marine heatwave days under continued global warming, the study concludes.