Century Old Data Helps Study Climate Change
May 28, 2013

135-Year-Old Data Helps Understand Climate Change

Lee Rannals for redOrbit.com - Your Universe Online

Ocean data collected over 135 years ago by the crew of the HMS Challenger oceanographic expedition has helped confirm global warming.

Researchers from NASA and the University of Tasmania used the data to provide further confirmation that humans have played a part in today's changing global climate. The team combined the ship's measurements of ocean temperatures with modern observations from the international Argo array of ocean profiling floats. They used state-of-the-art climate models to get a picture of how the world's oceans have changed over the last century.

The Challenger voyage was the world's first global scientific survey of life beneath the ocean surface. During this expedition, scientists measured ocean temperatures, lowering thermometers hundreds of feet deep on ropes.

"The key to this research was to determine the range of uncertainty for the measurements taken by the crew of the Challenger," said Joshua Willis, a JPL climate researcher and NASA project scientist for the upcoming US/European Jason-3 oceanography satellite, scheduled to launch in 2015.

"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. So, while the uncertainty was large, the warming signal detected was far greater."

Uncertainties during the 135-year-old research adventure were caused by the limited areas measured during the trip, the actual depths the thermometers reached, and the likely natural variation in temperatures that could have occurred during each trip.

"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," said researcher Will Hobbs of the University of Tasmania's Institute for Marine and Antarctic Studies and the Australian Research Council's Centre of Excellence for Climate System Science.

"Currently, scientists estimate the oceans absorb more than 90 percent of the heat trapped by greenhouse gases, and we attribute the global warming to anthropogenic causes."

Challenger's measurements revealed that thermal expansion of sea water caused by global warming has contributed to about 40 percent of the total sea level rise seen in tide gauges from 1873 to 1955. The remaining 60 percent was likely to have come from the melting of ice sheets and glaciers.

"This research adds yet another suite of compelling data that shows human activity continues to have a dramatic influence on the Earth´s climate," said Hobbs, lead author of the paper which was published in the latest edition of the journal Geophysical Research Letters.

The latest study confirms the results of similar research performed last year by scientists with Scripps Institution of Oceanography at University of California, San Diego and National Oceanography Center. Researchers from this study were the first to compare the temperatures taken during the Challenger's voyage and data from modern day readings.