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Warming Seas Accelerate Sea-Level Rise and Threaten Marine Life
The world's oceans are getting warmer and more acidic.
They have absorbed much of the extra heat and carbon dioxide produced by human activities.
Sea levels are rising faster than they did in the past.
Hotter seas can make heatwaves on land stronger, especially at night.
Warm water is also harming coral reefs and changing tiny ocean plants called phytoplankton.
Many coral reefs recently experienced temperatures that can cause bleaching.
Four emperor penguin colonies failed to raise chicks during a year with very little sea ice.
The Mediterranean and Black Sea have experienced unusually strong and lasting heatwaves.
Scientists say these changes show that the ocean is changing quickly.
Global sea levels rose about 3.8 millimeters annually since 1999 and 4.2 millimeters annually from 2012 to 2025.
The ocean has become 17% more acidic in 40 years and absorbed about 90% of excess planetary heat.
Record marine heatwaves are affecting the Mediterranean and Black Sea, with warming extending below the surface.
From January 2023 to September 2025, 84% of coral reefs experienced bleaching-level heat stress.
Four emperor penguin colonies in Antarctica had complete breeding failures during record-low sea ice in 2022.
- Who
- Marine ecosystems, coral reefs, emperor penguins and people exposed to climate-related heat and air pollution are affected; Mercator Ocean International reported the findings.
- What
- Oceans are warming, becoming more acidic, rising faster and contributing to ecological damage and extreme weather.
- Where
- The changes are global, with notable impacts in the Mediterranean Sea, Black Sea and Antarctica.
- When
- The report cites trends since 1999 and 2012, coral-reef impacts from January 2023 to September 2025, and penguin breeding failures in 2022.
- Why
- Humanity's greenhouse-gas pollution has caused the ocean to absorb about one-third of released carbon dioxide and around 90% of additional trapped heat.
Key facts
- Sea-level rise since 1999
- About 3.8 millimeters per year
- Sea-level rise, 2012-2025
- About 4.2 millimeters per year
- Ocean acidity
- The global ocean became 17% more acidic over 40 years
- Ocean heat absorption
- About 90% of additional heat trapped by greenhouse-gas pollution
- Coral-reef heat stress
- 84% of the world's coral reefs experienced bleaching-level heat stress from January 2023 to September 2025
- Emperor penguin colonies
- Four colonies recorded total breeding failures in 2022
- Mediterranean warming
- The Mediterranean Sea warmed by 0.32°C per decade
Quotes
Pierre Bahurel
Director general of Mercator Ocean International, which published the report
“The ocean is transforming before our eyes”
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