In short, the NOAA’s scientists concluded there was no warming pause or “hiatus” after accumulating new surface temperature data and making corrections to old data that it knew were imperfect.
The results reported in the study comprise an ongoing, decades-long effort to assemble the best possible record of global surface temperatures and determine the rate of global temperature change.
These new results convincingly demonstrate global warming has continued over the last 15 years, when the earlier data suggested it had slowed down.
“Adding in the last two years of global surface temperature data and other improvements in the quality of the observed record provide evidence that contradict the notion of a hiatus in recent global warming trends,” said Thomas Karl, director of NOAA’s National Centers for Environmental Information and study lead author.
Scientists who view climate data through a longer-term lens have never really taken the pause argument seriously. Some referred to the alleged pause as a “faux pause”. There has not been and isn’t now a slow-down in warming averaged over periods of at least 30 years.
Even before NOAA’s new study was published, data simply exhibited a slow-down in the rate of warming, rather than an actual stoppage. The data indicated that the 2000s were warmer than the 1990s which were warmer than the 1980s, and so forth. And 2014 was the warmest year on record.
A useful analogy for the recent course of temperatures is the path of an unruly dog on a long leash walking up a hill. The dog may stray downward for short lengths even as it pulled up and achieves new heights at regular intervals.
This study essentially provides insight on those short lengths – or the erratic movements of the dog – which most influence the rate of temperature change over short time intervals. It’s important work – as it shows warming over the last 15 years carried on despite forces like volcanoes, particle pollution, the sun, and ocean cycles that were pulling the Earth in a cooling direction.
But there are some thornier scientific issues with respect to short-term warming trends sure to remain hotly contested.
John Christy, the University of Alabama-Huntsville climate scientist who has constructed and studied temperature records of the lower atmosphere using satellite data, says atmospheric data do not exhibit the short term warming seen in Karl’s analysis.
“The six bulk-atmospheric temperature datasets agree that essentially nothing [no warming] has happened since the big El Niño of 97-98,” Christy said in an email. “If Karl’s work holds up…, this will only add to the puzzle of diverging surface and atmospheric temperatures which stands in contrast to model expectations.”
Karl said during a press call that NOAA had not yet analyzed whether his new surface-based results were harmonious with atmospheric data but said the warming seen in recent years would bring the observed temperature record in closer agreement with model forecasts.