"Ocean heating is a very important indicator of climate change, and we have robust evidence that it is warming more rapidly than we thought," said Zeke Hausfather, who is a graduate student in the Energy and Resources Group at the University of California, Berkeley and one of the report’s co-authors.
"While 2018 will be the fourth warmest year on record on the surface, it will most certainly be the warmest year on record in the oceans, as was 2017 and 2016 before that," Hausfather said.
According to climate scientists, more than 90% of Earth’s excess heat, which gets trapped in the atmosphere by insulating greenhouse gases, accumulates in the world's oceans.
The new report relies on four studies that were published between 2014 and 2017, that gave more precise estimates of ocean temperatures in recent years. Together with their new data, the new report both updates past research, and should provide a better estimate for the future.
The new fleet of floating robots, called Argo, has been key to providing the more accurate numbers. The report explains that these robotic data collectors “drift throughout the world's oceans, every few days diving to a depth of 2,000 metres and measuring the ocean's temperature, pH, salinity and other bits of information as they rise back up.”
Argo "has provided consistent and widespread data on ocean heat content since the mid-2000s," the report said.
The data provided by the new analysis puts ocean warming on pace with recent measurements of rising air temperature. If there are no changes to the current rate of greenhouse gas production, the oceanic models “predict that the temperature of the top 2,000 metres of the world's oceans will rise 0.78 degrees celsius by the end of the century," it said.
While seemingly small, that change in average temperature will raise sea levels by 30 centimetres, due to thermal expansion, a phenomena that causes water to swell as it warms. That is a larger rise in sea levels than anything caused so far by melting glaciers and ice sheets.
The warmer sea -water is threatening to life in several ways. For instance the extra warmth can reduce oxygen in the oceans and cause harm to coral reefs that are nurseries for fish, the scientists said. Warmer seas also release more moisture that can stoke more powerful storms, and increase the pace of melting ice in places like Antarctica and Greenland.
Almost 200 nations plan to phase out fossil fuels this century under the 2015 Paris climate agreement to limit global warming. But US President Donald Trump, who wants to promote US fossil fuels, plans to pull out of the pact in 2020.