Global ocean temperatures spike to record levels as El Niño nears

• Andrew Freedman, author of Axios Generate

•  Updated May 1, 2023 - 

Data: ClimateReanalyzer.org; Note: Average reflects 1982-2011 mean; Chart: Rahul Mukherjee and Simran Parwani/Axios

Since mid-March, the world’s oceans have been hotter than at anytime since at least 1982, raising concerns among some climate experts about accelerated warming.

Why it matters: Hotter oceans are hugely consequential for land areas, since they can contribute to more frequent and severe extreme weather and climate events, from deluges to heat waves.

• In addition, the temperature spike could be a sign that warming is speeding up in ways that climate models failed to anticipate.

Zoom in: While the global average sea surface temperature record is noteworthy and far-reaching, it’s not a reason to lose sight of the bigger picture, climate scientists told Axios.

• The sea surface temperature spike, detected by a network of ships, buoys and satellites, is likely due to the combination of an emerging El Niño in the tropical Pacific, and another trend that scientists are far more concerned about.
• When a La Niña event gives way to an El Niño, as is happening now, large amounts of ocean heat that had been lurking beneath the ocean surface is drawn upwards, according to Michael Mann, a climate scientist at the University of Pennsylvania.
• The result, Mann told Axios via email, is “a sizable increase” in tropical Pacific and global ocean surface temperatures during the transition.
• "La Niña buries some ocean heat below the surface and El Niño brings that heat back to the surface,“ Mann said.

Context: El Niño events are defined by above average ocean temperatures in the equatorial tropical Pacific, along with myriad shifts in weather patterns.

• Such ocean and atmosphere cycles are naturally occurring, and help temporarily accelerate, or in the case of La Niña, slow the rate of climate change.
• This is part of the reason the long-term surface temperature record resembles a staircase, rather than a straight line.

Threat level: The steady and record-setting accumulation of ocean heat throughout the water column, not just at the surface, actually has climate scientists more concerned than the recent sea surface temperature spike.

• Researchers like Mann and Kevin Trenberth of the National Center for Atmospheric Research (NCAR) told Axios this is a clearer sign of human-caused global warming than the ongoing record sea surface temperatures.
• The oceans absorb more than 90% of the extra heat from the Earth’s atmosphere due to greenhouse gas emissions from burning fossil fuels and other causes.
• Ocean heat content, measured in a column of water from the surface down to 2,000 meters (6,561 feet) deep, hit a record high in 2022; this is altering vital ocean currents that distribute heat and nutrients around the world, a recent study found.

The intrigue: The ocean surface temperature spike also reflects the fact that since the last major El Niño in 2016, global average surface temperatures on land and sea have increased.

• This means the 2023 El Niño is elevating global average temperatures from a higher starting point, making it easier to set records.
• This is like a basketball player playing on a court with a steadily higher floor, making it easier to dunk the basketball.
• This may be why 2023 has already seen record ocean temperatures surpassing 2016’s numbers, and why this trend may be here to stay throughout the duration of the projected El Niño.

What they're saying: "2023 is off to an alarming start, even before El Niño conditions fully develop later this year," Kim Cobb, a climate scientist at Brown University, told Axios via email. She noted that even a moderate El Niño is likely to lead to a new global temperature record.

• "Given the current pace of warming, however, even a new record will likely be surpassed in a matter of years. The planet is warming so fast now, even a natural cycle as strong as the El Niño-Southern Oscillation is beginning to be lost in the noise," Cobb said.

What we’re watching: How global average surface temperatures evolve during the course of the projected El Niño, which is anticipated to take hold between the summer and fall and potentially become a strong event.