Global ocean temperatures have reached a record high as El Niño injects extra heat into our already-warming world.

On Saturday (Aug. 22), the daily global average sea surface temperature (SST) was hotter than at any time since records began in 1979, according to the European Union's Copernicus Climate Change Service.

"This record is another clear signal of an ocean under growing stress," Samantha Burgess, the strategic lead for climate at Copernicus, said in a statement. "El Niño is adding heat to the system, but it is doing so on top of decades of human-driven warming. As ocean temperatures continue to rise, the risks to marine ecosystems and coastal communities also increase."

Human activities are driving global warming through the widespread and continued burning of fossil fuels, along with other activities that emit carbon dioxide (CO₂) and other greenhouse gases into the atmosphere. These gases trap heat by absorbing radiation.

Now, El Niño, officially underway as of June 11, is temporarily piling on additional warming. El Niño is the warm phase of a multiyear natural climate pattern, marked by unusually warm waters in the Pacific Ocean. The pattern typically boosts global temperatures and fuels disruptive weather, but this time, the conditions appear to be supercharged.

Researchers have warned that we're on the cusp of a likely historic super El Niño, with the potential to bring about a humanitarian crisis and possibly push an already-stressed climate ecosystem across a critical threshold.

A new record

Copernicus estimates global SST using satellites with temperature-measuring sensors. These showed that the SST hit 21.1 degrees Celsius (69.98 degrees Fahrenheit) Saturday, surpassing the previous high of 21.09 C (69.96 F), recorded in 2024 — the hottest overall year on record. The 2024 records were fueled by Earth's last El Niño, which was on the cusp of the "super" threshold, so not as extreme as what's forecast this time.

The latest SST is particularly eye-catching because it's unusual to have a record daily high so late in the year. The hottest daily temperatures are typically recorded in March and April, after the Southern Hemisphere's summer, Copernicus representatives wrote in the statement.

Copernicus representatives noted that the record is consistent with long-term warming and the emergence of an extreme El Niño event. The new data is also in line with what Copernicus has documented in recent months. Both June and July saw record-high average SSTs for their respective months. The rising temperatures highlight that our ocean is "under unprecedented strain," the statement noted.

A warming ocean means increased sea level rise and a higher risk of marine heat waves, according to Copernicus. Rising sea levels threaten coastal communities around the world. Meanwhile, the warmer waters harm coral reefs and other key marine ecosystems, which, in turn, affects food webs and the people who depend on these systems. Ocean warming also influences our weather systems and fuels global warming, which causes more ocean warming.

Super El Niño

El Niño conditions are still ramping up, and we won't know their full extent until later this year and next year. However, the National Oceanic and Atmospheric Administration's Climate Prediction Center forecasts a more than 90% likelihood of very strong El Niño conditions emerging in the fall and winter.

Last week, the U.K.'s Met Office announced that this year's El Niño will be the largest in living memory and likely the biggest since the 19th century.

"We should be clear that this is an unprecedented event," Adam Scaife, head of long-range forecasting at the Met Office, said in an Aug. 21 statement. "I have never seen an El Niño signal this intense in our forecasts."

A strong El Niño doesn't guarantee more severe weather or other impacts, but the risks are higher with a stronger event. The Met Office noted that the summer monsoon season in India, which is one of the regional weather patterns affected by El Niño, is already experiencing "well below" normal levels of rainfall.

In the U.S., El Niño often brings warmer winters to Northern states, while Southern states are more likely to experience stormier weather. However, every El Niño is unique.