New study; more proof
By Summit Voice
SUMMIT COUNTY — A detailed new modeling study of ocean temperatures reinforces the conclusion that observed warming is due to the buildup of heat-trapping greenhouse gases in the atmosphere.
The scientists at Lawrence Livermore National Laboratory, together with international collaborators, said their results show that observed ocean warming over the last 50 years is consistent with climate models only if the models include the impacts of observed increases in greenhouse gas during the 20th century.
“By using a “multi-model ensemble,” we were better able to characterize decadal-scale natural climate variability, which is a critical aspect of the detection and attribution of a human-caused climate change signal,” said Livermore Lab researcher Peter Gleckler, lead author of the new study that appears in the June 10 edition of the journal, Nature Climate Change.
“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.”
The new research is not the first study to identify a human influence on observed ocean warming, but it is the first to provide an in-depth examination of how observational and modeling uncertainties impact the conclusion that humans are primarily responsible.
“We have taken a closer look at factors that influence these results,” Gleckler said. “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.”
The group looked at the average temperature (or heat content) in the upper layers of the ocean. The observed global average ocean warming (from the surface to 700 meters) is approximately 0.025 degrees Celsius per decade, or slightly more than .10 degrees Celsius over 50 years.
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 percent of the heat accumulated over the past 50 years as the Earth has warmed.