Human activities that produce greenhouse gases, like the burning of fossil fuels, have driven warming in the upper ocean over the past 50 years, a new study finds.

Prior research had suggested that natural factors alone could not account for ocean warming during that period. But the latest research, published Sunday in the journal Nature Climate Change, takes a more detailed view.

An international team of researchers, led by climate scientist Peter Gleckler of the Lawrence Livermore National Laboratory, used multiple climate models and a high-quality set of observations to study the pattern of warming in the upper ocean.

They found that the observed pattern could not be produced by natural influences on Earth's climate -- but it did match the predictions of climate models that took into account the influence of greenhouse gases produced by human activities.

During the study period, the upper 2,300 feet of the ocean warmed by about 0.45 degree Fahrenheit per decade.

"We found no evidence that simultaneous warming of the upper layers of all seven seas can be explained by natural climate variability alone," Gleckler said in a statement. "Humans have played a dominant role."