Between 1998 and 2012, the average global temperature of the ocean seemed to hold steady, halting its decades-long climb. Known as the “global warming hiatus,” this phenomenon was a source of confusion for climate scientists and a talking point for climate change skeptics. In June 2015, however, researchers from the National Oceanic and Atmospheric Administration published a paper explaining the hiatus. The study suggested that the older ship-based collection methods were slightly off and corrected the numbers for measuring error—an act that erased the supposed hiatus.
The study set off a political firestorm, Jeff Tollefson reported for Nature in October of that year. Texas Republican Lamar Smith, the head of the House of Representatives Committee on Science, Space and Technology, claimed the study was part of a conspiracy. He requested the data used for the study and any communications associated with it. “NOAA needs to come clean about why they altered the data to get the results they needed to advance this administration’s extreme climate change agenda,” Smith said at the time. NOAA refused to hand over the documents, and the study has remained controversial ever since.
But a new independent study published in the journal Science Advances evaluated NOAA’s 2015 temperature recalibration, concluding that their corrections were accurate. “Our results mean that essentially NOAA got it right, that they were not cooking the books,” lead author Zeke Hausfather of the University of California Berkeley’s Energy and Resources Group says in a press release.
The researchers examined ocean temperatures not only collected from ocean buoys, but also satellites and autonomous instruments called Argo floats. The results of this analysis fall in line with NOAA’s recalibrated data from the 2015 paper—all pointing toward no hiatus in climate warming.
Phil Plait at Slate reports that collecting water temperature data from ships is problematic because the vessels use a wide variety of sampling methods. Some ships grab water samples from the intakes used to cool the engines, which means the water is usually slightly warmer than the surrounding ocean. Some use buckets thrown over the side. And most of the samples come from various depths. Over time shipping routes have also changed, throwing off datasets.
The new study relies only on techniques where those variables are known and can be controlled. “These results serve as a robust, independent validation of the NOAA temperature record, and show us that the new NOAA temperature record is probably the best estimate of global ocean temperatures over the last 15 years,” Hausfather says in a video statement.
The latest study also serves as a reminder of how the science works. “Science is a cumulative and continuous process," NOAA climatologist Huai-Min Zhang told Smithsonian.com's Sarah Zielinski in 2015. "[T]his is reflected in our continued improvements to the land and ocean surface temperature datasets.”