Fueling speculations of a climate change hiatus are data showing that from about 1998 to 2012, global temperature rise appeared to plateau, based on NOAA’s Extended Reconstruction Sea Surface Temperature dataset. This so-called pause has been puzzling scientists as well as prompting skeptics to say that human-induced global warming, after all, is a mere hoax.
Now a new study has surfaced to say that, no, that data isn’t proof of a hiatus. Across Earth, the oceans have been warming at a relatively steady clip over the last 50 years.
Lead author Dr. Zeke Hausfather, a data scientist from the University of California Berkeley, clarifies that warming appears in both datasets in practically the same way — confirming the integrity of the NOAA dataset. However, further evidence showed that ocean temperatures have warmed steadily without a pronounced slowdown.
“A fair bit of the apparent hiatus seems to be due to problems in our ocean measurements, and not a real thing," Hausfather told The Christian Science Monitor over the phone.
Global Warming Pause: An Illusion?
Detailing their findings in the journal Science Advances last Wednesday, Hausfather’s team revisited the data after political chaos erupted in 2015, when the errors were first identified. They discovered that NOAA was right despite the flak they received.
In June that year, NOAA updated its dataset, with National Centers for Environmental Information Director Thomas Karl and his NOAA colleagues pointing to a critical flaw in the old database. ERSST version 3b, the said previous version, had a cooling bias over the 15-year period and showed global temperatures as lower than actual. In that controversial research, Karl’s team called the hiatus “an illusion.”
“[Scientists at the NOAA] weren’t cooking the books. They weren’t bowing to any political pressure to find results that show extra warming,” Hausfather said, adding that the scientists tried their best to “work with messy data.”
Hausfather and the NOAA team agreed that changing technology caused the skewed data. Sea surface temperatures, for long decades, were tracked on ships. This changed in the mid-1990s when researchers started to use thermometers on buoys as a new strategy. The buoys, however, take colder measurements than the previous technique, and scientists in the previous dataset version did not adjust for the difference.
When this problem surfaced, the NOAA scientists calculated the difference and weighted the numbers differently to come up with version 4, which revealed that warming was actually more than twice as that on version 3b.
The results triggered great controversy, with some politicians suggesting that the team manipulated data out of political motives.
How Scientists Confirmed The 2015 Study
What Hausfather’s team did is to do things a little differently, studying trends in data from various sources independently rather than putting composite datasets together as other agencies do. The trends are tracked in sources that include data from buoys, ships, and satellites.
Indeed, from 1998 to 2012, temperatures did show some slow rising than predicted in climate models. The slowdown has been attributed to different factors, including the El Niño cycle, multiyear ocean cycles, and even the post-Soviet reforestation in Russia.
A massive El Niño event that occurred before that 15-year timeframe, for instance, would have made the following years appear relatively cold, while La Niña could have also helped drive the temperature reading slow. Certain small volcanoes too that were excluded in models could have had their share in the cooling effect, Hausfather explained.
For Karl — the lead scientist in the controversy-rocked 2015 paper — the recent findings emphasize the need for independent measurements in order to tackle observational uncertainties, he noted in his email to the Monitor.
Whatever slowdown occurred in the 2000s, it also appears to have stopped by now, with the last three years, from 2014 to 2016, breaking all records as the hottest year ever in the modern temperature data.
Photo: NASA Goddard Space Flight Center | Flickr