Humans Behind Global Ocean Warming, Say Scientists

Scientists have discovered that humans are the major culprits behind global ocean warming, according to a Lawrence Livermore National Laboratory (LLNL) report.

An international team of scientists has discovered that humans are one of the major factors behind global ocean warming. They discovered this when they were analysing and observing ocean warming over the last 50 years.

Though this new research is not the first study to identify a human influence on observed ocean warming, it is the first to provide an in-depth examination of how observational and modelling uncertainties impact the conclusion that humans are primarily responsible, say scientists.

"We have taken a closer look at factors that influence these results," said Peter Gleckler, climate scientist at the Lawrence Livermore National Laboratory, in a statement. "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."

Scientists studied the average temperature or heat content in the upper layers of the ocean. They found that the average global ocean warming (from the surface to 700 m) is approximately 0.025 C per decade or slightly more than 1/10th of a degree Celsius over 50 years.

The study also revealed that the sub-surface ocean warming is noticeably less than the observed earth surface warming, primarily because of the relatively slow transfer of ocean surface warming to lower depths. Nevertheless, because of the ocean's enormous heat capacity, the oceans likely account for more than 90% of the heat accumulated over the past 50 years as the earth has warmed.

In the study, scientists examined the causes of ocean warming using improved observational estimates. They also used results from a large multi-model archive of control simulations (that don't include the effects of humans, but do include natural variability). By combining the data, scientists found that increase in greenhouse emission over the past 50 years has led to a spike in global ocean warming.

"By using a multi-model ensemble, we were better able to characterise decadal-scale natural climate variability, which is a critical aspect of the detection and attribution of a human-caused climate change signal. What we are trying to do is determine if the observed warming pattern can be explained by natural variability alone," Gleckler said.

"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," he concluded.