New research found there was, in fact, a nearly 15-year “hiatus” in global warming in the early part of the 21st Century, suggesting it could have been caused by natural variability in the atmosphere’s energy balance.
What’s more is climate scientists with Germany’s Max Planck Institute found there’s too much uncertainty in observational data to determine the true cause of the “hiatus” in warming.
Scientists argue that “unless the uncertainty of observational estimates can be considerably reduced, the true origin of the recent hiatus may never be determined.”
“That’s an important sentence, because it demonstrates that despite many claims to the contrary, CO2 induced forcing of the planetary temperature is not the control knob, and natural variability remains in force,” veteran meteorologist Anthony Watts wrote of the Max Planck study on his blog Watts Up With That.
Max Planck scientists found hiatuses in global warming can be caused by relatively small changes in ocean energy balance, which can originate from the top of the atmosphere or the ocean.
“This is the true dilemma at the heart of the hiatus debate: the variability in ocean heat content alone has no power to explain the hiatus, and the measure that can—the surface-layer flux divergence—is dwarfed by observational uncertainty,” researchers wrote in their study, led by scientist Christopher Hedemann.
For years, scientists have debated the existence of the “hiatus” in global warming — a period from 1998 to 2012 with little to no statistically significant warming.
Many in the more alarmist camp considered the debate “settled” after the National Oceanic and Atmospheric Administration (NOAA) published a study claiming the “hiatus” was an artifact of biases in the way scientists measured sea surface temperatures from ships and buoys.
That study, led by NOAA scientist Tom Karl, found “corrected and updated global surface temperature data … do not support the notion of a global warming ‘hiatus.’”
Karl’s study was highly criticized by experts on all sides of the global warming debate, including those skeptical of man-made global warming.
Criticism reached its height after House lawmakers launched an investigation into the study to see if it was rushed to support former President Barack Obama’s climate agenda. A political battle ensued after Republicans on the House Committee on Science, Space and Technology subpoenaed NOAA for records on the study.
The Karl study came under fire again after former NOAA scientist John Bates blew the whistle on his former boss, claiming Karl put his “thumb on the scale” to get results to debunk the “hiatus” to bolster Obama’s agenda and international climate talks.
NOAA is bringing in outside experts to review the Karl study and take appropriate actions if necessary.
But Karl’s arguments are once again being challenged by the scientific community. Hedemann and his colleagues indirectly took on the Karl study, arguing studies attributing the “hiatus” to data artifacts face a big problem — “the gap between observations and models persists.”
“The observed trend deviated by as much as −0.17°C per decade from the CMIP5 (Coupled Model Intercomparison Project Phase 5) ensemble-mean projection —a gap two to four times the observed trend,” reads Hedemann’s study. “The hiatus therefore continues to challenge climate science.”
“There are hundreds of such hiatuses (364, or 2.4% of all 15,200 trends)—subject to historical forcing but due entirely to internal variability—distributed across all time periods in the ensemble,” Hedemann and his colleagues wrote of their analysis of 100 climate models.
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