> At a Glance
> – Oceans absorbed 23 zettajoules of heat in 2025, a new record
> – This marks eight consecutive years of record-breaking ocean warming
> – Energy absorbed equals 12 Hiroshima bombs exploding every second
> – Why it matters: The oceans store over 90% of excess atmospheric heat-driving climate change impacts worldwide
For the eighth year running, Earth’s oceans have set a new benchmark for heat absorption. A global research team reports the 2025 total surpassed all previous measurements since the 1960s, underscoring the planet’s relentless warming trajectory.
Record-Breaking Numbers
The study, released in Advances in Atmospheric Science and led by John Abraham of the University of St. Thomas, shows oceans soaked up 7 zettajoules more in 2025 than in 2024. Put another way, that energy could:
- Boil 2 billion Olympic pools
- Power the planet’s electrical needs 200 times over
- Match 12 Hiroshima bombs detonating each second-Abraham’s go-to analogy
> “Last year was a bonkers, crazy warming year-that’s the technical term,” Abraham quipped.
Where the Heat Hides
Oceans swallow over 90% of trapped greenhouse heat. While surface temperatures fluctuate with events like El Niño and La Niña, deeper waters steadily accumulate warmth through global circulation. In fact, 2025’s sea-surface readings dipped slightly below 2024’s all-time high, yet total ocean heat content still surged.
Zeke Hausfather, Berkeley Earth scientist and co-author, explains:
> “Ocean heat content is in many ways the most reliable thermostat of the planet. That’s where all the heat is going.”
| Metric | 2024 | 2025 |
|---|---|---|
| Additional ocean heat (zettajoules) | 16 | 23 |
| Sea-surface rank | Hottest on record | Slightly cooler |
| ENSO influence | Strong El Niño | Weak La Niña |
Data Sources
More than 50 scientists across the U.S., Europe, and China pieced together the estimate using:
- 3,500+ Argo floats profiling depth and temperature
- Readings from buoys, ships, satellites
- Tags on seals and other marine mammals that dive under ice
- Historical records dating back to the 1960s and the HMS Challenger voyage in the 1870s
Raphael Kudela, UC Santa Cruz ocean scientist not involved in the work, praised the multi-method consistency and warned:
> “Even if we stopped using fossil fuels today, it’s going to take hundreds of years for that heat to circulate through the ocean. We’re going to pay this cost for a very, very long time.”
Key Takeaways
- Ocean warming sets a new record every year because oceans absorb the bulk of planetary heat
- Surface temperatures only tell part of the story; deep-ocean storage drives long-term climate change
- Lag effect means centuries of commitment-today’s emissions heat tomorrow’s oceans
As data keep climbing, the oceans’ role as Earth’s primary heat sink grows ever clearer-and the need to curb greenhouse emissions becomes ever more urgent.
