Record-Breaking Ocean Heatwave

October 22, 2025

Share to Google Classroom

This summer, the waters of the North Pacific Ocean became the hottest ever recorded.

Between July and September 2025, sea temperatures in this huge region were more than 0.25°C warmer than the previous record in 2022. The affected area is around ten times larger than the Mediterranean Sea.

Scientists say climate change makes ocean heatwaves more likely, but they are puzzled by how extreme and long-lasting this one has been. Known as the “warm blob”, this hot patch in the ocean is unusual and may even make the start of winter in the UK colder than normal.

Zeke Hausfather, a climate expert from Berkeley Earth, said the size and strength of the warming is “quite remarkable” and likely not caused by natural weather changes alone.

Usually, ocean heat is mixed by winds, but this summer’s weaker winds allowed more heat to stay at the surface. However, scientists believe something more is happening.

One possible reason is a change in shipping fuel rules. Before 2020, ships used dirty oil that released sulphur dioxide, a gas that formed tiny particles in the air. These particles reflected sunlight, helping to keep the planet cooler. Cleaner fuels now produce fewer of these particles, which may allow more heat to stay in the ocean.

Cleaner air in places like China might also be contributing, since less pollution means less sunlight is being reflected away from Earth.

LEARNING OPTIONS