Scientists have long suspected that they're warming, but the limitations of data collection have prevented them from making a definitive claim. But now an international team of researchers say it has smoothed out problems with the data.
Presenter: Timothy McDonald
Speaker: Dr John Lyman, Joint Institute for Marine and Atmospheric Research at the University of Hawaii; Dr Susan Wijffels is a principal research scientist for marine and atmospheric research at the CSIRO
TIMOTHY MCDONALD: Much of the world's atmospheric heat is absorbed by the oceans.
The lead author of the study Dr John Lyman says the oceans provide the clearest indication of the state of global warming.
JOHN LYMAN: The ocean acts as a sink for 80 to 90 per cent of the heat that comes in at the top of the atmosphere and is trapped by our planet. And so it really is the bellwether for how much global warming has occurred.
TIMOTHY MCDONALD: Until recently it's been very difficult to pin down the extent of ocean warming. Most data was collected by devices known as expendable bathythermographs which are usually dropped from cargo ships.
John Lyman says there's many problems with them.
JOHN LYMAN: They were originally designed for warfare to determine the sound (inaudible) in water in order to track submarines. So since then we've tried to use them for climatological data and we have to correct them. And so there's five different corrections that are out there.
And this one is kind of like I said a meta study that uses all those five corrections to kind of give a better idea of the uncertainty we have in that correction.
TIMOTHY MCDONALD: Since 2004 there's been a much better way to take the ocean's temperature. Argo is a set of 3,000 floating robots that send back regular temperature measurements.
Dr Susan Wijffels is a principal research scientist for marine and atmospheric research at the CSIRO. She says the Argo program has for the first time allowed for accurate temperature readings in the southern hemisphere.
SUSAN WIJFFELS: There's a coalition of about 20 nations or so that are deploying these. Australia is a major player in that observing system.
And it means for Australia in particular that the southern hemisphere oceans are actually being measured properly for the first time in history.
TIMOTHY MCDONALD: Argo also has its biases and limitations but its readings are considerably more accurate.
John Lyman says that his team figured out the possible margins of error for both the Argo measurements and those taken from the expendable bathythermographs.
He says the study makes it clear that the imperfect equipment can't account for the rise in temperature.
JOHN LYMAN: We can see with that uncertainty that there has definitely been significant warming, that warming as a signal is six times larger than the uncertainty we measured.
TIMOTHY MCDONALD: John Lyman says oceanic warming is in the order of 0.16 of a degree Celsius. He says that might not sound like much but it's actually very significant.
JOHN LYMAN: Five-hundred 100-watt light bulbs per person on earth burning continuously - that would be the trend we've seen over the last 16 years just being sucked up by the ocean.
But I like to think of it in units of bombs that were dropped on Hiroshima and that would be over about 16 years two billion of those bombs. So it's a heroic job the ocean does sucking up that signal at the top of the atmosphere.
TIMOTHY MCDONALD: Susan Wijffels says oceanic warming could have a significant impact, especially for Australia.
SUSAN WIJFFELS: If we continue to emit at those very high levels there are a lot of very serious implications for our environment - potentially quite large sea level rise part of which is driven by ocean warming and the expansion of the ocean due to that warming; but also for the marine environment such as coral reefs.
So if we continue to emit at these very high levels we can expect into the next few decades fairly serious consequences.
TIMOTHY MCDONALD: John Lyman says the study can't explain why the increase in warming seems to have slowed in recent years.
He says it may be due to new equipment but it could also be a natural fluctuation within the warming trend.