Why we need to start categorizing marine heat waves like hurricanes

By Alistair Hobday

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Marine heat waves are the early warning systems for these longer-term changes. Given the range of biological, economic and political impacts associated with intense marine heat waves, we need a naming convention and a consistent way to measure the size of these events, as is the case for hurricanes. Naming and categorizing marine heat wave events will help researchers, communicators and the public to better understand change in the ocean. Today, each group of scientists around the world describes marine heat waves differently, so even comparing different events can prove difficult.

Colleagues from an international working group on marine heat waves and I have recently proposed a simple naming convention based on geography and year to enhance scientific and public awareness of these marine events. Thus “The Blob” would become the bland “Northeast Pacific 2015 Marine Heat Wave,” but it would be obvious when and where it occurred and we can thus distinguish each event around the world, facilitating comparison and communication.

We also developed a categorization scheme that is similar to methods used to describe atmospheric heat waves and hurricanes. Definitions of Category I, II, III and IV marine heat waves are based on the level to which water temperatures exceed local averages.

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Using this definition and classification, we discovered a long-term increase in the occurrence of all marine heat wave categories. In particular, Category II events have increased by 24 percent over the past 35 years. If climate change continues to warm the ocean, we may eventually need to add Category V and VI events in the future, in what will be a very warm and uncomfortable world.