135-year-old data obtained by the crew of the HMS Challenger oceanographic expedition is now providing further confirmation of anthropogenic climate change, thanks to a new analysis done by NASA, along with researchers from several top universities.
The ocean temperature measurements taken by the HMS Challenger were combined with modern measurements taken by the Argo array of ocean monitors, and put into “state-of-the-art climate models, to get a picture of how the world’s oceans have changed since the Challenger’s voyage,” by researchers from The University of Tasmania, Sandy Bay; and NASA’s Jet Propulsion Laboratory.
For those that don’t know, the HMS Challenger was an expedition, which lasted from 1872 to 1876, and was created with the intention of doing the first global scientific survey of the life in the world’s oceans. As part of the search for ocean life, researchers also measured ocean temperatures, by using ropes to drop thermometers hundreds of meters down into the ocean.
“The key to this research was to determine the range of uncertainty for the measurements taken by the crew of the Challenger,” said Josh Willis, a JPL climate scientist and NASA project scientist for the upcoming U.S./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.”
These uncertainties about the measurements taken by the HMS Challenger are a result of the relatively limited range covered during the voyage; the imprecision with regards to the depths that the thermometers were lowered to; and the probable natural variation in temperatures in each region.
“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 and lead author 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% of the heat trapped by greenhouse gases, and we attribute the global warming to anthropogenic (human-produced) causes.”
The new analysis also found that “thermal expansion of sea water caused by global warming contributed about 40% of the total sea level rise seen in tide gauges from 1873 to 1955. The remaining 60% was likely to have come from the melting of ice sheets and glaciers. Prior to this research, climate models offered the only way to estimate the change before the 1950s.”
The new results are published in the journal Geophysical Research Letters.