They say it means the Earth is more sensitive to fossil fuel emissions than estimated. What are the implications of the finding?
The researchers involved in the study believe the new finding will make it much harder to keep within the temperature rise targets set by governments in the Paris agreement. Recently the IPCC spelled out clearly the benefits to the world of keeping below the lower goal of 1.5C relative to pre-industrial levels .
This new study says that will be very difficult indeed.
What have these scientists done differently?
Since 2007, scientists have been able to rely on a system of almost 4,000 Argo floats that record temperature and salinity in the oceans around the world.
But prior to this, the methods used to measure the heat in the ocean had many flaws and uncertainties.
Now, researchers have developed what they say is a highly precise method of detecting the temperature of the ocean by measuring the amount of oxygen and carbon dioxide in the air. This allows them to accurately measure ocean temperatures globally, dating back to 1991, when accurate data from a global network of stations became available.
The key element is the fact that as waters get warmer they release more carbon dioxide and oxygen into the air.
"When the ocean warms, the amount of these gases that the ocean is able to hold goes down," said Dr Resplandy.
"So what we measured was the amount lost by the oceans, and then we can calculate how much warming we need to explain that change in gases.
