New studies have been coming to light that say that the apparent pause in the increase in ocean temperatures between 1998 and 2014 may never have happened to begin with, with the revised data instead showing a steady increase through that period.
According to a NOAA study that was released last year, the discrepancy came about due to the use of ship-based temperature readings, as opposed to temperatures recorded by ocean buoys. Buoys have a tendency to report lower temperatures than their ship-based counterparts, and are more accurate and consistent in their readings. In the 1990s, most readings were taken from ships, but now 85 percent of temperature readings are now provided by buoy-based sensors.
A more recent study, published in the journal Science Advances, corrected the data by taking this cold bias into account. These revised figures showed that ocean surface temperatures had warmed by 0.12ºC (0.22ºF) per decade, as opposed to the previously-accepted rate of 0.07ºC (0.13ºF). These figures illustrated a rate of increase that was "virtually indistinguishable" from the rate seen between 1950 and 1999 — and this revised data now precisely matched the figures coming from other sources.
Because of the discrepancy that originally appeared between the two sources, researchers had to decide on what the actual readings are. "Only a small fraction of the ocean measurement data is being used by climate monitoring groups, and they are trying to smush together data from different instruments, which leads to a lot of judgment calls about how you weight one versus the other, and how you adjust for the transition from one to another," explains Zeke Hausfather, the study’s lead author.
This new study used three independent data sets from buoys, robotic floats and satellites, to help avoid having any bias creep into the data.
"Our approach was to create three separate ocean temperature records from the three different instruments, and it turns out that all three agree really well with the new Noaa record," Hausfather continues.
"The conclusion is that Noaa got it right, the scientists at Noaa were not cooking the books or manipulating the data in any way and that three independent sets of data back up their results."
Climate change deniers in the U.S. House of Representatives did not take kindly to the notion that the warming trend was more pronounced than initially reported. They tried to subpoena the emails of the author of the NOAA study, accusing them of fraud, but the agency refused to comply with their demands.
"If people disagree with things they should ask other scientists to look into it rather than demanding access to scientists’ emails," says Hausfather.