Science/AAAS - Much-Touted Global Warming"Pause" Never Happened
What if the missing heat has been there all along? In 2013, the Intergovernmental Panel on Climate Change (IPCC) flagged an odd phenomenon: Atmospheric temperature data collected over the past few decades suggested that global warming had slowed down beginning around 1998. Global warming skeptics crowed, and scientists delved into the global climate system to find out where the missing heat had gone. But a new analysis suggests that the real culprits are the data themselves. When better corrections for various sources of bias are applied to the data, the authors say, the so-called global warming hiatus vanishes—and in fact, they argue, global warming may have sped up.
That won't startle some scientists, who say the “hiatus” was always a misnomer. “There is no hiatus or pause,” says climate scientist Michael Mann of Pennsylvania State University, University Park, who prefers the term “temporary slowdown.” But he and others do think something has changed since the late 1990s: Perhaps the deep waters of the Pacific and Atlantic oceans are storing more heat, or volcanic eruptions and pollution have been shading the planet and offsetting the warming. What's more, they note, 1998 was a particularly strong (and hot) El Niño year—not an ideal starting point for determining a subsequent trend. But the temperature data themselves—collected by a variety of techniques from land and sea—have also been a source of concern, says Thomas Karl, director of the National Oceanic and Atmospheric Administration's National Climatic Data Center in Asheville, North Carolina, and the lead author on the new paper published online this week in Science. Climate scientists have worked for years to improve corrections for bias in the data. “It's an ongoing activity,” Karl says.
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Another challenge was incorporating land-based readings from thousands of new measurement stations in regions that have long had scant coverage, particularly Asia, South America, and Africa. New data from these regions have been amassed over the past 5 years as part of the International Surface Temperature Initiative, which released its first report just last year.
In their paper, Karl's team sums up the combined effect of additional land temperature stations, corrected commercial ship temperature data, and corrected ship-to-buoy calibrations. The group estimates that the world warmed at a rate of 0.086°C per decade between 1998 and 2012—more than twice the IPCC's estimate of about 0.039°C per decade. The new estimate, the researchers note, is much closer to the rate of 0.113°C per decade estimated for 1950 to 1999. And for the period from 2000 to 2014, the new analysis suggests a warming rate of 0.116°C per decade—slightly higher than the 20th century rate. “What you see is that the slowdown just goes away,” Karl says.
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http://news.sciencemag.org/climate/2015/06/much-touted-global-warming-pause-never-happened?rss=1
