Researchers in Norway recently found that global warming is less severe than previously predicted by the United Nations climate authority, causing skeptics to argue that a growing body of data is on their side while experts cast doubt on the results.
“It’s one in a substantial number of papers appearing in scientific literature within the last year or two, reducing the forecast global warming for the 21st century,” Patrick Michaels, director of the Center for the Study of Science at the Cato Institute, told The Daily Caller News Foundation in an interview.
“This is just more evidence that the sensitivity was overestimated,” he added.
However, some have urged caution in interpreting the results in the study, as it has not yet been peer-reviewed.
“But this episode underlines the problems of so-called science by press release,” writes Dr. Roz Pidcock for the Carbon Brief. “With such a complex and sometimes controversial topic, research findings need to be carefully treated. As with all scientific research, if results are not yet published or peer reviewed, they are worth treating as preliminary.”
“You should be very skeptical — it has no good basis,” James Hansen, climatologist and head of the NASA Goddard Institute for Space Studies, told TheDC News Foundation in an email.
Bloomberg reports that the United Nations Intergovernmental Panel on Climate Change found that global temperatures may rise 3 degrees Celsius — with a range of 2 degrees Celsius to 4.5 degrees Celsius — by 2050 if carbon dioxide levels doubled. However, after applying post-2000 temperatures, Norwegian researchers found that may rise only 1.9 degrees Celsius.
“The Earth’s mean temperature rose sharply during the 1990s,” said Terje Berntsen, a University of Oslo professor who worked on the study. “This may have caused us to overestimate climate sensitivity.” Climate sensitivity refers to the total amount of global warming projected if atmospheric carbon dioxide levels are doubled.
Eystein Jansen, research director at the Bjerknes Centre for Climate Research, told New York Times blogger Andrew Revkin that, “it is way to early to say that this study has any more weight than other studies with low or higher sensitivity. My bet still goes along the 3 degree line as the most plausible, all things considered.”
However, Michaels argues that since the 2007 IPCC estimate, studies lowered their warming forecast because the sensitivity of temperature to CO2 emissions has been overestimated. In a Washington Times op-ed, Michaels provides a partial list:
“Richard Lindzen gives a range of 0.6 to 1.0 C (Asia-Pacific Journal of Atmospheric Sciences, 2011); Andreas Schmittner, 1.4 to 2.8 C (Science, 2011); James Annan, using two techniques, 1.2 to 3.6 C and 1.3 to 4.2 C (Climatic Change, 2011); J.H. van Hateren, 1.5 to 2.5 C (Climate Dynamics, 2012); Michael Ring, 1.5 to 2.0 C (Atmospheric and Climate Sciences, 2012); and Julia Hargreaves, including cooling from dust, 0.2 to 4.0 C and 0.8 to 3.6 C (Geophysical Research Letters, 2012).”
“Forecasts for the 21st century that were made in the late 1990s had better be revised downward because it’s very clear that we are going to go pretty close to a quarter of a century, at least, without a warming trend,” Michaels told TheDC News Foundation.
Michaels made the same claim in a 2002 study that also found that global warming “will be modest and near the low end” of what the IPCC had projected in it’s third assessment on climate change. Now, a growing number of scientists are starting to revise down their warming estimates for the 21st century.
“It’s appropriate to jump off a ship when it begins to take on water,” Michaels said, “If you look at the monthly temperature anomalies from the University of East Anglia you see no significant trend in any direction going back to the fall of 1996 which would put us at 17 years of no trend.”
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