See How Marine Heat Waves Are Spreading Across the Globe
Sea surface temperatures in 2024 broke records and about a quarter of the world's oceans are experiencing temperatures that qualify as a marine heat wave.
By Delger Erdenesanaa
Graphics by Harry Stevens
This article was produced in partnership with the Pulitzer Center's Ocean Reporting Network.
In recent decades, the oceans have warmed. Marine heat waves, once rare events, have become more common.
One particularly intense event known as 'the Blob' lasted years and devastated plankton populations, starving millions of fish and seabirds and damaging commercial fishing.
Recently, high temperatures have persisted. In January of 2024, the share of the ocean surface experiencing a heat wave topped 40 percent.
Unusual heat waves have occurred in all of the major ocean basins around the planet in recent years. And some of these events have become so intense that scientists have coined a new term: super marine heat waves.
'The marine ecosystems where the super marine heat waves occur have never experienced such a high sea surface temperature in the past,' said Boyin Huang, an oceanographer at the National Oceanic and Atmospheric Administration in an email.
The seas off the coasts of the United Kingdom and Ireland experienced an unusually intense marine heat wave, one of the longest on record, starting in April and the temperature rise happened much earlier in the year than usual. Australia and its iconic coral reefs were recently struck by heat waves on two coasts.
Scientists define marine heat waves in different ways. But it's clear that as the planet's climate changes, the oceans are being fundamentally altered as they absorb excess heat trapped in the atmosphere from greenhouse gases, which are emitted when fossil fuels are burned.
Hotter oceans are causing drastic changes to marine life, sea levels and weather patterns.
Some of the most visible casualties of ocean warming have been coral reefs. When ocean temperatures rise too much, corals can bleach and die. About 84 percent of reefs worldwide experienced bleaching-level heat stress at some point between January 2023 and March 2025, according to a recent report.
Last year, the warmest on record, sea levels rose faster than scientists expected. Research showed that most of that rise in sea levels came from ocean water expanding as it warms, which is known as thermal expansion, not from melting glaciers and ice sheets, which in past years were the biggest contributors to rising seas.
Source: NOAA Physical Sciences Laboratory
Source: NOAA Physical Sciences Laboratory
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