Marine Heatwaves are Becoming Longer and More Frequent

Caitlin Dempsey


Researchers, looking at in situ temperature recordings and satellite observations, have found that marine heatwaves are becoming more frequent and longer lasting.

What are marine heatwaves?

A marine heatwave is defined as periods of prolonged high sea surface temperatures [1]. More specifically, this was defined in a recent study as sea surface temperatures (SST) in the 90th percentile based on a 30-year average for five consecutive days for a given area of the ocean.

Impact of heatwaves on oceans  

MHWs can have a devastating impact on ocean ecosystems, resulting in coral bleaching, loss of kelp forests, marine deaths due to heat stress, reduced chlorophyll levels, and shifts in species habitat ranges.  

The rise in greenhouse gases is considered to be a major attributor to the subsequent rise in sea surface temperatures [2].

Free weekly newsletter

Fill out your e-mail address to receive our newsletter!

Satellite data and ocean heatwaves

Researchers compiled temperature data from satellite observations, and both monthly and daily on site temperature readings to look at frequency and duration of marine heatwaves (MHWs) in order to understand trends and patterns.

Researchers used in situ temperature recordings dating back to 1900 and satellite imagery dating back to 1982 to look at global trends.  They found that between 1925 to 2016, “global average marine heatwave frequency and duration increased by 34% and 17%.”

A graph showing in the total number of days where there was an ocean heatwave.  Red bars show El Niño periods and purple bars show La Niña time periods.
Source: Oliver et al, 2018

The study:

Oliver, E. C. J., Donat, M. G., Burrows, M. T., Moore, P. J., Smale, D. A., Alexander, L. V., … Wernberg, T. (2018). Longer and more frequent marine heatwaves over the past century. Nature Communications, 9(1), 1324.


[1] Hobday, A. J., Alexander, L. V., Perkins, S. E., Smale, D. A., Straub, S. C., Oliver, E. C., … & Holbrook, N. J. (2016). A hierarchical approach to defining marine heatwaves. Progress in Oceanography, 141, 227-238.

[2] Bindoff, N. L., Stott, P. A., AchutaRao, K. M., Allen, M. R., Gillett, N., Gutzler, D., … & Mokhov, I. I. (2013). Detection and attribution of climate change: from global to regional.

See Also

Photo of author
About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.