The researchers from America, India, Japan and Australia say theirs is the most comprehensive work to date on how the oceans have warmed.
Correspondent: Emily Woodgate
Speakers: Dr John Church, study co-author, CSIRO fellow with the Centre for Australian Weather and Climate Research; Professor Nathan Bindoff, oceanography expert
EMILY WOODGATE: The frigid waters of the Southern Ocean swirl around Tasmania's western and southern coastlines at this time of year. But it's not as cold as it was 50 years ago, according to an international team of scientists.
US-led research published today in the journal Nature Climate Change claims to prove once and for all that not only is global ocean warming real - it's the fault of humans.
Dr John Church is one of the co-authors, based in Hobart.
JOHN CHURCH: It's the most comprehensive study of changes in ocean heat content to date by quite some margin.
EMLY WOODGATE: Dr Church is the CSIRO fellow with the Centre for Australian Weather and Climate Research.
He says researchers from America, Australia, Japan and India examined a dozen different models used to project climate change. Past studies have only looked at a couple at a time.
They compared these with observations of ocean warming from the past 50 years.
JOHN CHURCH: And this has allowed the group to rule out that the changes are related to natural variability in the climate system.
EMILY WOODGATE: He says there's simply no way the upper layers of every ocean in the world could have warmed by more than one-tenth of a degree Celsius through natural causes alone.
JOHN CHURCH: Natural variability could only explain 10 per cent or thereabouts of the observed change.
EMILY WOODGATE: Professor Nathan Bindoff is one of the world's foremost oceanography experts and has been a lead author on past Intergovernmental Panel on Climate Change assessment reports.
NATHAN BINDOFF: Ninety per cent of the temperature change stored in the whole of the earth's system is stored in the ocean, so global warming is really an ocean warming problem.
EMILY WOODGATE: He says the new research balances the man-made impacts of warming greenhouse gases and cooling pollution in the troposphere against natural changes in the ocean's temperature and volcanic eruptions.
NATHAN BINDOFF: This paper is important because for the first time we can actually say that we're virtually certain that the oceans have warmed and that warming is caused not by natural processes but by rising greenhouse gases primarily.
EMILY WOODGATE: And he says the evidence of global warming is now unequivocal.
NATHAN BINDOFF: We did it. No matter how you look at it, we did it. That's it.