The HMS Challenger set sail during 1872 on the world's first scientific mission to explore life beneath the surface of the oceans. As part of their research, the crew of Challenger lowered thermometers hundreds of feet beneath the ocean's surface. Examination of data from that four-year-long scientific mission lends evidence supporting a rise in global sea temperatures since that time.

Researchers from Jet Propulsion Laboratories (JPL) and the University of Tasmania combined the data from that mission with information obtained from an international network of ocean-profiling floats called Argo. Both sets of measurements were then entered into climate modeling software, designed to model how ocean temperatures have changed since that time.

"Our research revealed warming of the planet can be clearly detected since 1873 and that our oceans continue to absorb the great majority of this heat," Will Hobbs of the University of Tasmania said. Hobbs was lead author of the paper reporting the results of the study.

From 1873 to 1955, average sea levels rose. As water warms, it expands in a process called thermal expansion. This new comparison of data from the Challenger with the Argo measurements suggests that 40 percent of this 82-year rise in sea levels was due to thermal expansion. The remainder is likely the result of the melting of ice sheets and glaciers.

As is so often the case with older data, there were uncertainties surrounding the validity of the data collected by the Challenger expedition.

"After we had taken all these uncertainties into account, it became apparent that the rate of warming we saw across the oceans far exceeded the degree of uncertainty around the measurements," Josh Willis, JPL climate scientist and co-author of the paper, said. "So, while the uncertainty was large, the warming signal detected was far greater."

When the team was accounting for these uncertainties, they used the most conservative estimates possible whenever they did not have the exact data they needed for the comparison. Researchers estimate that they may have underestimated the actual warming of the oceans by as much as 17 percent. Temperatures in the eastern half of the Pacific Ocean were most-prone to error.

The Journal Geophysical Research Letters published the results of the study.