All oceans across the world are warning at growing pace and the heat is already having devastating consequences on marine life as well as intensifying extreme weather events, according to new research, which examined data going back to the 1950s.
A global team of researchers looked at temperatures from the ocean surface to 2,000 meters deep. The study, published in the journal Advances in Atmospheric Sciences, showed that the past decade was the warmest on record for global ocean temperatures, with the hottest five years ever recorded happening in the last five.
“The upward trend is relentless, and so we can say with confidence that most of the warming is man-made climate change,” said Kevin Trenberth, a senior scientist in the Climate Analysis Section at the National Center for Atmospheric Research.
The study compared ocean temperature data from the last three decades (1987-2019) to the three decades before that (1955-1986) and found that the rate of warming has increased 450%, reflecting a major increase in the rate of climate change.
Using an energy unit common in physics, the researchers found that the oceans absorbed 228 sextillion joules of heat in the past 25 years. That is equivalent to 3.6 billion Hiroshima-size atom bomb explosions to the oceans, “irrefutable proof of global warming,” according to Lijing Cheng, co-author of the study.
The fact that the oceans are warming has a whole set of consequences. It is causing marine heatwaves, fuels hurricanes and coastal downpours, increases harmful toxin-producing algal blooms and also contributes to heat waves on land, according to the researchers.
“The ocean heat content changes are the primary memory of global warming,” Trenbeth said. “This manifestation of global warming has major consequences. Hurricanes pump the ocean heat content into the atmosphere in the form of moisture. That results in extreme and record rainfall from storms.”
The average temperature for the upper 2000 meters of the oceans increased by 0.12 degrees Celsius from 1960 to 2019, according to the study. Nevertheless, the ocean surface, where hurricanes draw their energy, and the air just above it has warmed almost 1 degree Celsius from the pre-industrial era.
This is almost irreversible on a human timescale, Trenberth said. “Imagine mixing a pot of hot and cold water in the sink. It gets warm, and you can never get the hot or the cold back,” he said. Nevertheless, there’s hope, as the speed of warming is entirely dependent on the world’s actions on climate change.
The new study of ocean heat content strengthens other recent signs of global warming. The past decade was the warmest on record since measurements started, and 2019 ended up the second-warmest year on record, although it was the warmest in the oceans.