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Rights: The University of Waikato
Published 30 June 2010

Dr Phil Sutton of NIWA outlines what the Argo project has told us about the ocean so far. By comparing Argo data with older measurements, it has become clear that the ocean has warmed, and salty parts have got saltier. There have also been changes in the water cycle that fit predictions made by climate change models.


Argo giving that real-time or near real-time measurements of the global ocean, for the first time, you can look at what is happening, for instance, with ocean heat content.

Now, the ocean has taken up about 90% of the changes in heat content in the past few decades, and obviously everybody is very concerned about changes in heat content in the world in terms of global warming. If you don’t measure the ocean, you can’t understand the global heat content at all.

So Argo, since 2004, we are for the first time being able to look at changes in heat content on a decadal level, and if we can keep Argo going long enough, we will be able to look on longer-term timescales.

The main way that people have tried to look at longer-term change so far is by comparing Argo data with data that we have collected from research vessels as part of the World Ocean Circulation Experiment [WOCE] in the late 80s, early 90s, and that was when there was fairly good global coverage but not nearly to the level that Argo is.

And what comparing the modern Argo data with the older WOCE data has told is that the ocean has warmed. It’s also telling us that there have been changes in the hydrological cycle – the salty parts of the ocean have gotten saltier and the fresh parts of the ocean have gotten fresher – so that basically is consistent with the hydrological cycle accelerating a little bit, in other words, more rain where it’s already rainy or even drier where it’s already dry, and that is the sort of pattern that is predicted from global models in the warming world.

The Argo data is absolutely critical if you want to understand climate change or even climate variability. Argo is already explaining a lot of what goes on in the El Nino ENSO cycle that we didn’t understand before in the oceans. So climate variability at the decadal kind of timescale and climate change at longer timescales – you need Argo for that. It is also giving – with its complete coverage of the ocean and the ocean movement data from the float trajectories – is for the first time ever, we are working out more of how the ocean works.

Scripps Institution of Oceanography, UCSD
NASA/Goddard Space Flight Centre Scientific Visualization Studio/courtesy of