A 2020 study in the journal Science concluded that marine heat waves have increased more than 20-fold as a result of climate warming. The authors found that in the first decade after satellites began recording ocean temperatures (i.e., after 1981), there were 27 large marine heat waves, with an average duration of 32 days and an average peak temperature anomaly of 8.5°F; in the 2010s, there were 172, which lasted 48 days on average with an average peak temperature almost 10°F above normal.
Much remains unclear about marine heat waves. For example, explains Nicholas Bond, research scientist at the University of Washington and Washington's state climatologist, there is the question of why so many persist for weeks or months. "There must be something else going on that helps maintain them," he says. He notes that one explanation is that as the ocean surface warms, it radiates heat into the atmosphere that prevents cloud cover from forming, exposing the seawater to increased sunlight and further warming.
However, enough is known about marine heat waves for scientists to be gravely concerned about their potential impacts. Of special note is the fact that those impacts can last long after the heat waves have disappeared. After three years of the Blob, the waters of the northeastern Pacific began to cool in 2016; but years later, scientists are still determining the extent to which the region's ecosystem is likely to return fully to its pre-Blob status. Similarly, notes Scannell, who is a data scientist with Jupiter Intelligence, Inc., following the 2010-11 Western Australia event, "lots of kelp (巨藻) forests died, and it takes literally decades for those ecosystems to bounce back".
Eric Oliver, a scientist from Dalhousie University in Nova Scotia, Canada, expressed his own opinion about the potential impact of the heat waves in tropical waters. "I think that's really a tough issue," he says. Life in the tropics, he notes, is adapted to "quite a narrow range of temperatures. So that's where things can get really messy. We can have complete shifts in tropical systems."
