Unknown oceanic heat waves have emerged as another worrying indicator of climate change.
A buoy floating in the Mediterranean Sea off the coast of the Balearic Islands recorded 29 degrees Celsius on June 19, a day after temperatures in many areas of Spain and France reached record highs (84 Fahrenheit).
According to Melanie Juza, a researcher with the Balearic Islands Coastal Observing and Forecasting System, which monitors marine temperatures daily across the Mediterranean, the unprecedented heat wave on land sparked a marine heat wave that is currently going on.
There has never been such an intense marine heat wave so early in the year, said Juza. We’re talking 26 degrees Celsius and more on the Balearic Sea on June 19 — it’s brutal.
Marine heat waves are relatively unknown to scientists, with research papers on these ocean temperatures starting to appear only in 2013. The phenomenon has subsequently emerged as a crucial indicator of climate change; for decades, oceans have acted as giant sponges, soaking up most of the extra heat in the atmosphere.
You see a greater increase in the frequency of severe heat waves with every additional degree of global warming compared with the changing frequency of other types of extreme weather, said Luke Harrington, a senior research fellow at the New Zealand Climate Change Research Institute. Marine heat waves are changing faster than land heat waves.
Since the 1970s, scientists have known that the oceans have absorbed 93% of the heat produced by greenhouse gases. They are also aware that after the 1990s, carbon dioxide storage and capture ceased keeping up with emissions. Understanding how much and how much more heat the oceans can store will be crucial to predicting how quickly the earth will warm in the following decades.
There are no climate deniers among oceanographers, said Andrew Pershing, director of climate science at the research nonprofit Climate Central, in Princeton, NJ. You just can’t be because the signal is so strong.
According to Samuel Somot, leader of the regional climate modeling team at French national forecaster Meteo France, high air temperatures, limited cloud cover, and no wind are causing marine heat waves.
Marine heat waves happen on top of the ongoing heating of the oceans, which is linked to global warming; that’s what’s making marine heat waves longer and more intense, he said. That’s why when atmospheric conditions lead to extremes at sea, these are higher than they were decades ago.
Although there isn’t a single definition for marine heat waves, most scientists think they happen when water temperatures climb to extremely high levels and stay there for at least five days. These occurrences disrupt water’s vertical circulation, which in turn impacts the oceans’ ability to absorb heat and carbon dioxide as well as the movement of nutrients essential to the survival of marine life.
The impacts on marine ecosystems are devastating, said Juza. They include coral bleaching, damage on sea prairies, harmful algae blooms, mass mortality of marine species and migration of species.
Even human activities like tourism and fishing suffer. For instance, the most recent marine heat wave in the Mediterranean occurred during the pricey and popular red tuna spawning season. While scientists are unsure how the intense heat will affect tuna eggs, they do know that posidonia, a Mediterranean seaweed that is a nursery for numerous species, is damaged by high temperatures.
One of the earliest investigations into the phenomena was spurred by the financial effects of a maritime heat wave on fishing. The local lobster market was devastated by a hot spell in the Gulf of Maine in 2012, which inspired the researchers to draw the following important conclusions:
Drawing lessons from events like the 2012 heat wave is critical for developing adaptation strategies that will enhance existing capacities to sustain marine ecosystems and fisheries in the context of climate change.