An anonymous reader shared this report from CNN:

Ocean surface heat is at record-breaking levels. Temperatures began climbing in mid-March and skyrocketed over the course of several weeks, leaving scientists scrambling to figure out exactly why.

Temperatures have fallen since their peak in April — as they naturally do in the spring — but they are still higher than they have ever been on record for this time of year…. The record may not seem huge — it’s nearly two-tenths of a degree higher than the previous record in 2016 — but given how much heat is needed to warm up this huge body of water, “it’s a massive amount of energy,” Matthew England, professor of ocean and climate dynamics at the University of New South Wales, Australia, told CNN… Some scientists are concerned the scale of these new records could mark the start of an alarming trend. Others say record-breaking temperatures like these are always concerning but to be expected given the human-caused climate crisis.

All agree the consequences are likely to be significant. Warmer oceans bleach coral, kill marine life, increase sea level rise and make the ocean less efficient at absorbing planet-warming pollution — the warmer oceans get, the more the planet will heat.

The science leader at the British Antarctic Survey told CNN that “it’s probably too early” to blame El Niño.” In fact, the world just emerged from a 3-year La Niña cooling event in March. So instead, CNN gets a different explanation fro Gregory C. Johnson, an oceanographer at the National Oceanic and Atmospheric Administration:

“It’s a little bit like we’ve had the freezer door open for a while and it’s helped to cool the planet,” Johnson said. But even while that freezer has been open, background temperatures have continued to rise. Now the freezer is closed, everything is hotter than before.

Later CNN adds that some scientists are concerned “climate change might be progressing in ways climate models have not predicted.”

One surprising reason could be the reduction of aerosols in the atmosphere. In 2020, regulations were introduced to limit the amount of sulfur in the fuel ships used — a policy aimed at addressing air pollution. Though air pollution has a significant impact on human health, it also acts as an artificial sunscreen and reflects sunlight away from the Earth. One theory is the absence of aerosols may have turned up the heat, said Karina von Schuckmann [an oceanographer at Mercator Ocean International in France].