Ocean temperatures are less influenced by year-to-year variations in the weather.
Researchers said this showed that, contrary to the claims of some sceptics, the world was warming at a...
In the Arctic, the warming oceans are also causing a serious decline in sea ice, which only compounds the ongoing threats of climate change such as sea level rise.
"Observational records of ocean heat content show that ocean warming is accelerating", said the scientists from China and the United States in the journal Science.
Past year is expected to be the hottest for the oceans on record - explaining the wild fires, severe storms, record breaking rains and droughts that swept the world.
When we see the effects of climate change around us, we mostly think about increasing temperatures in the atmosphere.
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About 93 percent of excess heat - trapped around the Earth by greenhouse gases that come from the burning of fossil fuels - accumulates in the world's oceans.
A key factor in the more accurate numbers is an ocean monitoring fleet called Argo, which includes almost 4,000 floating robots that "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", said the report. And warming oceans lead to a lot of other dire consequences, some immediately felt by humans and other creatures, and some more generally destructive to life as we've long known it.
"The fact that these corrected records now do agree with climate models is encouraging in that is removes an area of big uncertainty that we previously had", he said. According to Lijing Cheng, one of the study's authors, temperatures down to 2,000 meters rose about 0.1 degree Celsius (0.18F) between 1971-2010, according to Reuters. 2015 is next warmest, although 2016 was the hottest for the global mean surface temperature, but that was in part because of the huge El Niño event that took place: the extra heat at the surface was at the expense of the ocean which cooled off slightly.
The climate models project continuous ocean warming in the 21th century; how much depends on human actions to address climate change.
They drift across the world, every few days diving to a depth of 2,000 metres measuring temperature, salt and chemicals as they rise back up.
"If the ocean wasn't absorbing as much heat, the surface of the land would heat up much faster than it is right now", Malin Pinsky, an associate professor in the department of ecology, evolution and natural resources at Rutgers University, told The New York Times.