But what if all of those scientists are wrong? What if the tiny sliver of scientists that don't believe global warming is happening, or that human activities are causing it — that two to three percent of climate contrarians — are right?
That's the hypothetical question that a new study, authored by Rasmus Benestad, Dana Nuccitelli, Stephan Lewandowsky, Katharine Hayhoe, Hans Olav Hygen, Rob van Dorland, and John Cook, sought to answer. Published last week in the journal Theoretical and Applied Climatology, the study examined 38 recent examples of contrarian climate research — published research that takes a position on anthropogenic climate change but doesn't attribute it to human activity — and tried to replicate the results of those studies. The studies weren't selected randomly — according to lead author Rasmus Benestad, the studies selected were highly visible contrarian studies that had all arrived at a different conclusion than consensus climate studies. The question the researchers wanted to know was — why?
"Our selection suited this purpose as it would be harder to spot flaws in papers following the mainstream ideas. The chance of finding errors among the outliers is higher than from more mainstream papers," Benestad wrote at RealClimate. "Our hypothesis was that the chosen contrarian paper was valid, and our approach was to try to falsify this hypothesis by repeating the work with a critical eye."
It didn't go well for the contrarian studies.
The most common mistake shared by the contrarian studies was cherry picking, in which studies ignored data or contextual information that did not support the study's ultimate conclusions. In a piece for the Guardian, study co-author Dana Nuccitelli cited one particular contrarian study that supported the idea that moon and solar cycles affect the Earth's climate. When the group tried to replicate that study's findings for the paper, they found that the study's model only worked for the particular 4,000-year cycle that the study looked at.
"However, for the 6,000 years' worth of earlier data they threw out, their model couldn't reproduce the temperature changes," Nuccitelli wrote. "The authors argued that their model could be used to forecast future climate changes, but there's no reason to trust a model forecast if it can't accurately reproduce the past."
The researchers also found that a number of the contrarian studies simply ignored the laws of physics. For example, in 2007 and 2010 papers, Ferenc Miskolczi argued that the greenhouse effect had become saturated, a theory that had been disproved in the early 1900s.
"As we note in the supplementary material to our paper, Miskolczi left out some important known physics in order to revive this century-old myth," Nuccitelli wrote.
In other cases, the authors found, researchers would include extra parameters not based in the laws of physics to make a model fit their conclusion.
"Good modeling will constrain the possible values of the parameters being used so that they reflect known physics, but bad 'curve fitting' doesn't limit itself to physical realities," Nuccitelli said.
The authors note that these errors aren't necessarily only found in contrarian papers, and they aren't necessarily malicious. In their discussion, they offer a suite of possible explanations for the mistakes. Many authors of the contrarian studies were relatively new to climate science, and therefore may have been unaware of important context or data. Many of the papers were also published in journals with audiences that don't necessarily seek out climate science, and therefore peer review might have been lacking. And some of the researchers had published similar studies, all omitting important information.
These same errors and oversights, the authors allow, could be present in consensus climate studies. But those errors don't contribute to a gap between public understanding and scientific consensus on the issue, the researchers argued. The mistakes also seemed to be particularly present in contrarian studies, Nuccitelli wrote.
In the end, the researchers stressed the overall importance of reproducibility in science, both for consensus views and contrarian ones.
"Science is never settled, and both the scientific consensus and alternative hypotheses should be subject to ongoing questioning, especially in the presence of new evidence and insights," the study concluded. "True and universal answers should, in principle, be replicated independently, especially if they have been published in the peer-reviewed scientific literature."
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