The pace of global warming hasn’t slowed since 1998, a finding that contradicts a major United Nations study and challenges a key argument of skeptics of manmade climate change.
Temperatures since 2000 have risen at a pace that is “virtually indistinguishable” from the rate of the five preceding decades, researchers led by Thomas Karl at the U.S. National Oceanic and Atmospheric Administration said Thursday in the journal Science.
That challenges the biggest-ever UN study on warming published in September 2013, which found that the rate of temperature gains had fallen by more than half since 1998. Doubters of man’s influence on the climate have cited the reported slowdown as proof that the scientific understanding of climate change isn’t robust and steps to cut greenhouse gases aren’t worth the cost.
“A whole cottage industry has been built by climate skeptics on the false premise that there is currently a hiatus in global warming,” Mark Maslin, a climatologist at the U.K.’s University College London who wasn’t involved in Thursday’s study, said by e-mail. “The weight of evidence for anthropogenic change is overwhelming and this new study shows that the global warming hiatus was just wishful thinking.”
From 2000 to 2014, average global temperatures increased at a pace of 0.116 degrees Celsius a decade (0.209 degrees Fahrenheit), compared with a 0.113-degrees-a-decade pace from 1950 through 1999, according to Thursday’s report.
In 2013, the UN Intergovernmental Panel on Climate Change said global temperatures rose at 0.05 degrees a decade from 1998 through 2012, a slowdown from the 0.12-degrees-a-decade pace from 1951 through 2012.
“We would hope this would serve to inform the general public that temperatures today really are continuing to warm,” Karl, director of NOAA’s National Climatic Data Center, said on a conference call. While the trend may vary year to year, “we don’t see a good argument for substantial changes in the rate of increase.”
Skeptics have seized on 1998 because since then, the global average temperature hasn’t surpassed that year’s level by more than the statistical margin of error. Records by the UN’s World Meteorological Organization show that 2014, 2010 and 2005 were all warmer than 1998, though within the 0.1-degree margin of error.
In the U.S., Congressional Republicans and presidential candidates have cited the reported slowdown to argue against taking action on climate change.
“Satellite data demonstrate for the last 17 years, there’s been zero warming,” Senator Ted Cruz of Texas said in an NBC TV interview in March. Last year, Senator Marco Rubio of Florida told Fox News that global temperatures “have stabilized.”
Both have declared their candidacy for the Republican presidential nomination.
The UN has said the world needs to keep the global average increase to no more than 2 degrees to avoid dangerous changes including more intense droughts, heat waves and increased flooding.
In Thursday’s report, researchers evaluated historical data sets accounting for variations in the way surface temperatures at sea are measured, and incorporated more measurements in the fast-warming Arctic. They also adjusted for inconsistencies in which temperatures collected by ships are “systematically warmer” than those from buoys, as well as variations between two different ship-based measurements.
The analysis won’t resolve all questions about 21st century warming, said Tom Osborn, a professor of climate science at the University of East Anglia in Norwich, England. Other sets of temperature data still show a slowdown and scientists have discovered “intriguing” local phenomena including a cooling trend in parts of the Pacific, said Osborn.
“This new study suggests that the slowdown in the rate of warming may be much less pronounced,” than previously thought, he said in an e-mailed statement.
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