The ‘blob’ is back — except this time it stretches across the entire North Pacific

CNN Climate | September 19, 2025
By Andrew Freedman

People gather along the La Jolla coastline as the sun sets on the horizon of the Pacific Ocean while smoke from Southern California wildfires fills the air on August 5, 2025, in San Diego, California. (Kevin Carter/Getty Images)

A record-breaking and astonishingly expansive marine heat wave is underway in the Pacific Ocean, stretching about 5,000 miles from the water around Japan to the West Coast of the United States. The abnormally warm “blob” of ocean water, which is getting a significant boost from human-caused global warming, is affecting the weather on land and could have ripple effects on marine life.

The hot ocean waters around Japan contributed to that country’s hottest summer on record, which featured its all-time national maximum temperature record, set on August 5, at 107.2 degrees Fahrenheit.

On the other side of the Pacific, the ocean heat is also yielding higher humidity in northern California at the start of meteorological fall, and if it persists, could enhance rain and mountain snowfall from wintertime atmospheric rivers.

The sea surface temperature difference from average across the entire North Pacific smashed an all-time record for the month of August, with reliable data stretching back to the late 19th century.

What worries scientists is the repetitive nature of these events. As climate change causes more heat to be stored in the oceans, ocean temperatures are reaching new heights that could lead to more significant impacts from these heat waves like this.

The North Pacific warmed at the fastest rate of any ocean basin on Earth during the past decade, according to Michael McPhaden, a senior scientist at the National Oceanic and Atmospheric Administration.