The National Oceanic and Atmospheric Administration (NOAA) has been tracking MHWs since 1950. NOAA defines a MHW as a period of at least five consecutive days when SSTs are at least 4 degrees Fahrenheit (2.2 degrees Celsius) above the long-term average.
Since 1950, there have been 152 MHWs in the global ocean. The most recent MHW occurred in the Gulf of Maine in 2021. This MHW was the longest on record, lasting for 122 days.
The “blob” was a large area of unusually warm water in the North Pacific Ocean that persisted from 2013 to 2016. The blob was the largest MHW on record, covering an area of over 10 million square kilometers (4 million square miles).
The blob had a significant impact on the marine ecosystem in the North Pacific Ocean. It caused coral bleaching, fish kills, and changes in species distributions. The blob also contributed to the decline of the Pacific sardine population.
The blob was an unprecedented event, but it is likely that MHWs will become more common and more intense in the future due to climate change. Climate change is causing the ocean to warm at an accelerated rate, which is making MHWs more likely to occur.
