Marine heatwaves have become longer and more frequent over the last century, reports a study published in Nature Communications this week. The research shows that annual marine heatwave days have increased by 54% from 1925 to 2016, with an accelerating trend since 1982.

Prolonged periods of anomalously high ocean surface temperatures, known as marine heatwaves, are extreme climate events that can have detrimental effects on marine ecosystems leading to substantial ecological and economic impacts. Ongoing warming has been observed extensively in the upper ocean; however, trends in extreme temperatures have not been examined on a global scale.

Eric Oliver and colleagues analyse satellite and in-situ observations of sea surface temperature from 1900-2016 and show that between 1925-1954 and 1987-2016 marine heatwave frequency increased by an average of 34% and marine heatwave duration by 17% globally. They attribute this to a global increase in mean ocean temperatures, and although internal variability has a role at the regional level, it does not affect long-term trends.

The authors suggest that given the likelihood of continued ocean surface warming throughout the 21st century, and the accelerating trend observed in recent decades, we can expect a continued global increase in marine heatwaves in future, with implications for marine biodiversity.