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.
The UN Intergovernmental Panel on Climate Change (IPCC) says ocean warming has led to rising sea levels and contributes to increases in rainfall intensity, more violent storms and the destruction of coral reefs.
It is also a threat to biodiversity and one of the earth's major food supplies.
"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 co-author Zeke Hausfather, a graduate student in the Energy and Resources Group at the University of California, Berkeley.
Their report relied on four studies, published between 2014 and 2017 whose conclusions are based on measurements recorded by a fleet of some 4,000 floating robot monitors called Argo.
The robtos drift throughout the world's oceans, every few days diving to a depth of 2,000 meters and measuring the ocean's temperature, pH, salinity and other information.
Observations also are broadly consistent with models over the more-recent Argo period (post-2005) when the observational uncertainty is much smaller due to a vast improvement in the number and quality of observations: [5/6] pic.twitter.com/JOG4vF8RpIZeke Hausfather (@hausfath) 10 janvier 2019
Argo "has provided consistent and widespread data on ocean heat content since the mid-2000s," the report said.
The new analysis shows warming in the oceans is on pace with measurements of rising air temperature.
And if nothing is done to reduce greenhouse gases, "models predict that the temperature of the top 2,000 meters of the world's oceans will rise 0.78 degrees Celsius by the end of the century," it said.
Caution needed when interpreting results
David Whitehouse, the science editor for the Global Warming Policy Foundation, based in the UK says we must very careful when drawing conclusions.
"I think you've got to be very careful when splicing together two sets of data from two sets of instruments and trying to compare them", he told RFI, referring to the fact that the study in question pulled together measurements from before the Argo system was up and running.
"The past is full of people trying to do this and have had to be re-evaluated years later because we found out something else about the measurements made in the past and the measurements made today."
"They can make a case that the oceans are warming this way, provided you accept that they understand what's going on and I wouldn't say that we understand completely about the past instruments."
"The most sensible thing to do would be to stick to the data since 2006 which is quite good enough to give us a baseline with a coherent data set."
"If you just look at the Argo array itself, you cannot see this catastrophic, runaway ocean warming in just that data. So I know all scientists will say this, but I'd really like another 15 years of data in order to convince me."
"Personally, I'd like another section of data to see if this is us, or it's a combination of us and natural variability, and where we stand."