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Warming Oceans

Overall ocean heat levels and sea surface temperatures are increasing dramatically due to climate change. This increase is a clear indicator of climate change and warming atmospheric temperatures because 90% of global temperature rise occurs in the ocean.

Key Takeaways


90% of temperature rise occurs in the oceans

The world's oceans absorb over 90% of the temperature rise from climate change, which is why the oceans are warming.


Sea surface temperatures and ocean heat levels have been increasing

Sea surface temperatures have been increasing since 1880. Since 1957, ocean heat levels have also been increasing.


Scientists use many different measurement methods

Scientists use satellites, remote buoys, and remote sensors to measure heat changes, sea surface temperatures, and temperatures deeper in the ocean. These methods complement each other to make sure data are accurate.

What We Know

When greenhouse gases warm the atmosphere, 90% of this warming occurs in the ocean. That is because By measuring ocean warming, scientists get a clearer picture of climate change. Since 1957, oceans have absorbed over 326 zettajoules of energy. That is over eight times more than the energy humans used for electricity, heating, industry, etc.

Graph from EPA showing global sea surface temperature anomaly based on 1971-2000.
Sea surface temperature has increased substantially since the 1880s. This graph with data from NOAA compares the global temperature to the 1971-2000 average.

Ocean warming is happening at the same time as atmospheric warming. Ocean warming provides a second set of evidence for global temperature rise. Since 1880, sea surface temperatures have increased by 1.26ºC and are continuing to rise. The graph to the left shows this rise. As shown, even with some year-to-year variation, sea surface temperatures have continued to climb.

Similarly, the interactive graph below shows how pure ocean heat levels have increased by a stunning amount since 1957, when scientists began measuring them. With sea surface temperatures and ocean heat levels combined, there is no doubt that the world's oceans have been warming.

Ocean Heat Level Change, 1957-2017

The graph shows the change in ocean heat levels in zettajoules (a measure of enormous amounts of energy) at an ocean depth of 0-2000 meters.

Can't interact with the graph above? Click here!

How We Know

When early scientists began measuring sea surface temperatures in 1880, it was using a thermometer off ships across the world. Since then, technology has improved significantly. Now, researchers use a combination of satellite measurements, remote buoys, and robotic sensors that measure both sea surface temperature and ocean heat levels.

Satellites measure sea level increases and determine how much of that is due to warm ocean water expanding. From these measurements, computers calculate the heat levels of the ocean. In addition, remote buoys measure sea surface temperature across the world, while robotic sensors sink deep into the ocean to get measurements for up to 2,000 meters (like in the graph above). Researchers compare all of their measurements from different sources to verify that they make sense and are accurate, making sure there are no biases in the data. All of these methods combine to form a cohesive picture of ocean warming.


EPA. “Sea Surface Temperature: Climate Change Indicators.” Reports and Assessments. United States Environmental Protection Agency, April 2021.

LuAnn Dahlman and Rebecca Lindsey. “Climate Change: Ocean Heat Content.” NOAA, August 17, 2020.

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