The world's oceans are heating at the rate of two trillion 100-watt light bulbs burning continuously, providing a clear signal of global warming, according to new study assessing data from a global fleet of drifting floats.

The research, published on Tuesday in the journal Nature Climate Change, used data collected from the array of about 3500 Argo buoys from 2006-13 to show temperatures were warming at about 0.005 degrees a year down to a depth of 500 metres and 0.002 degrees between 500-2000 metres.

Oceans store about 93 per cent of the extra heat taken up by Earth. Credit:Max Mason-Hubers

Oceans south of the 20-degree latitude accounted for two-thirds to 98 per cent of the heat gain during the period studied, with three giant gyres in the southern Pacific, Indian and Atlantic oceans largely responsible for drawing down the extra warmth.

"The global ocean heat content right now is the most reliable metric of that radiation imbalance" between the energy received from the sun and what is radiated back to space, said Susan Wijffels, an oceans expert at the CSIRO and one of the report's authors.