Photograph by Pete McBride, Nat Geo Image Collection
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An abandoned boat casts a long shadow in the dry Colorado River delta. A new analysis of global sea and land temperatures shows there has been no pause in warming.

Photograph by Pete McBride, Nat Geo Image Collection

Science Challenges Claim That Global Warming Took a Hiatus

NOAA's reanalysis shows no slowdown in rising temperatures over the past 15 years, undercutting a favorite argument of climate change skeptics.

A reported pause in global warming—a mystery that has vexed scientists and delighted contrarians—was an illusion based on inadequate data, U.S. government researchers reported Thursday.

The findings by National Oceanic and Atmospheric Administration (NOAA) researchers that there was no warming "hiatus" over the past 15 years could reshape consensus science on recent climate change. The research undercuts an argument of pundits and politicians who oppose taking action.

In the new report, NOAA's team focused on an ever changing network of thousands of temperature-monitoring stations on land and on ships and buoys at sea around the world. The scientists replotted average annual surface temperatures since 1880 while accounting for changes and quirks in the readings, particularly anomalies from ocean ships and buoys. Their conclusion confirms that unrelenting warming has occurred since the mid-20th century, according to the study published in the journal Science.

"You have a trend in the 21st century, and you have a trend in the second half of the 20th century. According to our data, those trends are the same. We don't see a hiatus," says co-author Russell Vose, chief of the climate science division at NOAA's National Centers for Environmental Information.

The new findings refute an observation in the 2013 report of the United Nations' Intergovernmental Panel on Climate Change (IPCC.)  The IPCC used the term "hiatus," noting that the rate of warming from 1998-2012 was one-third to one-half slower than the rate of warming from 1951-2012.

NOAA's new analysis suggests that faulty numbers led to that assumption, which triggered widespread repercussions in the science and politics of climate change.

"We can try to put a nice face on it. We can try to soften it, but the reality is that there is no statistically significant hiatus, and there never has been," says Harvard science historian Naomi Oreskes.

Scientists have undertaken numerous studies to respond to opinion-shapers like conservative columnist George Will, who wrote in 2009 that "there has been no recorded global warming for more than a decade." Senator Ted Cruz (R-Texas), a presidential candidate, recently commented, "For the last 17 years, there's been zero warming."

Oreskes and a colleague counted more than 80 papers seeking to explain the hiatus and published in peer-reviewed journals. The journal Nature devoted two special issues to the topic early in 2014.

"A huge amount of scientific work and effort has gone into explaining a phenomenon which actually doesn't exist," Oreskes says.

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Gavin Schmidt, director of NASA's Goddard Institute for Space Studies, who was not involved in the new study, says it is interesting that tiny changes in data could erase the hiatus entirely. He points out that any look at how temperatures change over time is an estimate, so as more measurements are taken, understanding of potential biases improves and corrections are to be expected.

"The fact that such small changes to the analysis make the difference between a hiatus or not merely underlines how fragile a concept it was in the first place," Schmidt says.

But the new paper still leaves room for doubt among both researchers and those who dispute global warming in the political realm. Judith Curry—a professor at Georgia Institute of Technology's School of Earth & Atmospheric Sciences who has argued that temperature records have significant gaps—said by email that she is not convinced that NOAA's new methods have produced a more accurate view of the warming trend.

"This short paper in Science is not adequate to explain and explore the very large changes that have been made to the NOAA data set," she wrote. "The global surface temperature data sets are clearly a moving target. So while I'm sure this latest analysis from NOAA will be regarded as politically useful for the Obama Administration, I don't regard it as a particularly useful contribution to our scientific understanding of what is going on."

Marc Morano, publisher of the contrarian Climate Depot website and a former aide to Sen. James Inhofe (R-Oklahoma), says that NOAA's new study will have "virtually no impact in the climate debate." Cruz and others can continue to point to satellite data that still show a hiatus of more than 18 years. "This latest study merely adds to the dueling data sets and of course time lines in the climate debate," Morano said by email.

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Seabirds fly over melting Arctic ice pack in Svalbard, Norway.

In the new report, the NOAA team took into account that there are far more temperature-reading buoys deployed in the world's seas today than decades ago. The buoy readings over time have been found to be more accurate, so the buoys are given more weight in the new data set.

Also, the team corrected for a mistaken assumption that commercial ships since World War II measured ocean temperatures through ship engine intakes. NOAA's team now says many ships still measure ocean temperature the old-fashioned way—by lowering buckets into the water, much as young Benjamin Franklin did when he tried to chart the Gulf Stream on his trans-Atlantic journeys.

Adjustments to all of these anomalies in temperature gathering add up to what scientists believe is a more accurate picture—and one that shows consistent, unrelenting warming, the NOAA researchers say.

"A big part of our job is accounting for the fact that most of the observation systems we have were never put out there to monitor climate to begin with," Vose says. "They were looking at weather for aviation or agriculture, and the ocean monitoring was for ships that were interested in currents, not climate." Addressing all of these potential biases is "a neat challenge," he said.

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Interestingly, NOAA's corrections and reanalysis result in less global warming since the 1880s than the agency's uncorrected data showed: about 1.65 degrees Fahrenheit (0.92 Celsius) instead of 2.07 degrees Fahrenheit (1.15 Celsius). That's because the recalculations make temperatures higher in earlier years.

Vose says the research trying to explain the hiatus was not wasted. Studies examining ocean circulation and heat absorption, reduced solar activity, increased sulfur dioxide, and other factors that can cause cooling add valuable information and in "no way" conflict with the new data, he says.

"If those forces had not been in action, we might be seeing even larger temperature increases," he says.