Ocean warming caused by human activites, greenhouse gases

By Chelsea Whyte on June 12, 2012 7:12 PM EDT

Ocean
New research shows that human changes to the environment lead to increasing ocean temperatures. (Photo: Flickr.com/augustuzos)

The warming of the Earth's oceans is a sign of climate change, and while there's been many opinions on what caused that, scientists now say that the warming seen over the past 50 years is due to human activities.

A research team of Lawrence Livermore National Laboratory scientists and international collaborators looked into the average temperature in the upper layers of the ocean over the past several decades. The measured global average ocean warming, taking place from the surface down to 700 meters below sea level, is about 0.025 degrees Celsius per decade, which adds up to just over one-tenth of a degree Celsius over 50 years.

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Because of the ocean's capacity to hold heat, rising global water temperatures likely account for more than 90 percent of the heat accumulated over the past 50 years as the Earth has warmed.

The team used climate simulations to model what climate changes would result due to natural variability, and then looked at models that included human activities that contribute greenhouse gases to the warming atmosphere.

"What we are trying to do is determine if the observed warming pattern can be explained by natural variability alone," said lead author Peter Gleckler, an LLNL climate scientist.. "Although we performed a series of tests to account for the impact of various uncertainties, we found no evidence that simultaneous warming of the upper layers of all seven seas can be explained by natural climate variability alone. Humans have played a dominant role."   

While attributing global warming to humans is hardly a new conclusion, this study adds to research intended to tease apart the effects of natural climate cycles, which can occur over decades, from changes caused by human alterations to the environment, reports The Christian Science Monitor

And though this research isn't the first to suggest that humans play a role specifically in ocean warming, it's the first to provide an in-depth examination of how uncertainties in climate models and observed climate changes impact the conclusion that humans are primarily responsible.

"The bottom line is that this study substantially strengthens the conclusion that most of the observed global ocean warming over the past 50 years is attributable to human activities," Gleckler said.

The new study appears in the June 10 edition of the journal, Nature Climate Change.

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