In March, sea surface temperatures off the east coast of North America were as much as 13.8C higher than the 1981-2011 average.

"It's not yet well established, why such a rapid change, and such a huge change is happening," said Karina Von Schuckmann, the lead author of the new study and an oceanographer at the research group Mercator Ocean International.

"We have doubled the heat in the climate system the last 15 years, I don't want to say this is climate change, or natural variability or a mixture of both, we don't know yet. But we do see this change."

One factor that could be influencing the level of heat going into the oceans is, interestingly, a reduction in pollution from shipping.

In 2020, the International Maritime Organisation put in place a regulation to reduce the sulphur content of fuel burned by ships.

This has had a rapid impact, reducing the amount of aerosol particles released into the atmosphere.

But aerosols that dirty the air also help reflect heat back into space - removing them may have caused more heat to enter the waters.