(The author is a Reuters market analyst. The views expressed are his own.)

The world's oceans have absorbed more than 90 per cent of global warming since the mid-20th century, making accurate measurements of deep ocean temperatures vital to predicting how much global temperatures and sea levels are going to rise.

In 1999, a group of 30 countries launched the Argo programme as the first global, subsurface ocean observing system.

It will improve on the earlier patchwork of observations dating as far back as Britain's HMS Challenger in 1873, which dropped a weighted thermometer overboard on a hemp line 8 millimetres thick.

The Argo floats are rather more sophisticated with an inflatable chamber and a pump that changes the buoyancy of the float by changing its volume. It can sink from the surface to 2,000 metres depth and then resurface, measuring temperatures and salinity as it goes.