Most efforts to detect signs of global warming have been directed to signals in the air temperature field.
Breaking research conducted by Tim Barnett and David Pierce of Scripps Institution of Oceanography at the University of California, San Diego, has shown preliminary evidence of human-produced warming in the upper 3,000 meters of the world’s oceans.
Their findings are published in the April 13 edition of the journal Science.
Barnett and Pierce, with colleague Reiner Schnur, cross-referenced data from the U.S.-developed Parallel Climate Model (sponsored by the Department of Energy and the National Center for Atmospheric Research), which factors in the influence of greenhouse gases and direct sulfate aerosols over the last 50 years, and direct observations of heat content change in the ocean over the same period.
They found that as the climate model ocean temperature rose and penetrated into the depths of the oceans, the observed global ocean temperature down to 3,000 meters rose right along with it.
They note that the agreement between the model and the observations is remarkably similar in all the oceans.
"The initial results are certainly compatible at the 95 percent confidence level with the hypothesis that the warming observed in the global oceans has been caused by anthropogenic sources," said Barnett, a research marine physicist in the Climate Research Division at Scripps.
"Our results provide a broader foundation for claims that global warming has been observed and attributed to human activities."
Pierce notes: "This work also provides a new criterion for measuring the realism of computer climate models. As models are improved to better match ocean warming seen over the last fifty years, they should give better estimates of future climate change as well."
The research was supported by the National Oceanographic and Atmospheric Association Climate Change Data and Detection program and the U.S. Department of Energy, Office of Energy Research. Schnur was supported by the Max Planck Institut for Meteorology.