2017 Was The Warmest Year Ever For Oceans Across The Globe


Rachel Baxter

Copy Editor & Staff Writer

Sergey Uryadnikov/Shutterstock

Last year, the oceans were hotter than they’d ever been. For beach-goers this may sound like welcome news, but it’s really, really not. The rise in temperature signifies that not only our seas, but the rest of our planet too, are in trouble.  

The news comes from a new analysis of ocean temperatures by scientists at the Chinese Academy of Sciences in Beijing, which was published in the journal Advances in Atmospheric Sciences.


The study shows that in 2017, the seas were 1.51 × 1022 Joules warmer than in 2015, the second warmest year for the oceans on record. For scale, this amount of heat energy is 699 times greater than the electricity generated by China each year, so it’s pretty significant.

The warming of the oceans in 2017 occurred across most of the world, with the Atlantic and Southern Oceans being more affected than the Indian and Pacific Oceans.

While ocean warming threatens the inhabitants of the marine world, it is also a very good indicator of how fast the planet as a whole is heating up. “More than 90 percent of Earth’s residual heat related to global warming is absorbed by the ocean,” the paper reads.

“The last five years have been the five warmest years in the ocean. Measurements of ocean heating are a more reliable indicator than atmospheric measurements for tracking the vital signs of the health of the planet.”


Warming sea temperatures have all sorts of worrying knock-on effects, from reduced ocean oxygen to melting sea ice.  

Much underwater biodiversity is found in coral reef ecosystems, otherwise known as the rainforests of the sea. Reefs sustain endless species, from turtles and sharks to the iconic clownfish, and are known as some of the most biodiverse regions on our planet. But warming temperatures cause tiny coral polyps to expel the symbiotic algae essential for their survival, bleaching them and causing them to die. And when coral disappears, all manner of marine organisms start to fade away too.

Where coral has bleached, little else survives. Rich Carey/Shutterstock

Meanwhile, in the cooler Arctic Ocean, warming seas mean less ice, causing creatures like polar bears to travel too far to search for prey. On the other side of the planet, and the other end of the food chain, a warming Southern Ocean affects the distribution and survival of tiny creatures like krill, making it harder for whales and penguins to find them.   

And not only does ocean warming harm marine ecosystems, it also contributes to rising sea levels, as the warmer water expands. The temperature increase of 2017 made ocean levels rise by 1.7 millimeters, which may not sound like much, but is concerning nonetheless. Rising seas can lead to flooding, coastal erosion, soil contamination, and habitat loss for many species.


Many critics of climate change argue that temperature fluctuates naturally, and this is true to an extent. The phenomenon known as El Niño, which happens every few years, causes surface sea temperatures to naturally increase due to interactions between the oceans and the atmosphere. The opposite – El Niña – also occurs, causing surface sea temperatures to drop. Things like volcano eruptions can also naturally impact ocean temperatures.

However, the scientists involved in the new analysis found something worrying. While the data for 2017 alone can’t necessarily prove that climate change is occurring and that we are causing it, the overall trends from the last few decades can. In fact, the past five years have been the warmest on record.  

(upper) Change in global upper-level (0-2000 m) ocean heat content since 1958. Each bar shows the annual mean relative to a 1981-2010 baseline. (lower) Annual mean ocean heat content anomaly in 2017 relative to a 1981-2010 baseline. Lijing Cheng

As you’ve probably guessed, the warming of the seas is down to human activity, and the release of greenhouse gases like carbon dioxide. But we can turn the tide – by reducing our energy consumption and investing in renewable energy, we can slow this warming down and protect our oceans from further harm.


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  • climate change,

  • global warming,

  • oceans,

  • 2017,

  • rising sea temperatures