Tuesday, August 5, 2014

PolitiFudging climate change consensus

PolitiFact jumped on Republican congressional hopeful Lenar Whitney's recent claim that global warming is a hoax.

We're not going to delve into whether Whitney's claim was true or false, or even whether her YouTube video promoting her beliefs was a wise election strategy.  We're simply concerned in this case with the methods PolitiFact uses to support the claim of a scientific consensus backing climate change (a.k.a. global warming).

Among climate researchers most actively publishing scientific articles, at least 97 percent believe in anthropogenic climate change, found one 2009 study published in the Proceedings of the National Academy of Sciences, a scientific journal. The study examined published scientific articles and surveyed experts.
At Zebra Fact Check, I reviewed each of the evidences used to support the claim of a scientific consensus on climate change.

The study PolitiFact describes above was led by William R. L. Anderegg.  PolitiFact's description of this study is reasonably accurate, but glosses over the following concerns.  Anderegg and company deliberately narrowed the survey group down to the researchers publishing most actively.  That method allows intimidation of the editors of scientific journals to artificially establish the expertise of the survey group.  Part of the scandal discovered through the release of the East Anglia email concerned the efforts of scientists to keep journals from publishing articles by climate change skeptics.

It's manifestly obvious the study's methodology was designed to give added weight to the views of scientists who had published the most.  And that's not a good method for measuring scientific consensus in the field of study.

Another survey out of the University of Illinois found that 82 percent of earth scientists (out of more than 3,000 respondents) believe that global temperature shifts are human-caused. Among climate-specific earth scientists who responded, 97.4 percent said they believe in human-caused climate change.
In this case, PolitiFact and Lauren Carroll are simply guilty of bad reporting.  The survey PolitiFact used as its evidence, by graduate student Maggie Kendall Zimmerman and professor Peter T. Doran, concerned the answers to two questions:
1. When compared with pre-1800s levels, do you think that mean global temperatures have generally risen, fallen, or remained relatively constant?
2. Do you think human activity is a significant contributing factor in changing mean global temperatures?
In other words, 82 percent of earth scientists surveyed believe human activity is a significant contributing factor.  PolitiFact helpfully translates that into "human-caused."

Among earth scientists studying climate, 97.4 percent believe human activity is a significant contributing factor.  PolitiFact likewise translated that into believing climate change is "human-caused."

Thanks to the muddled definitions supported by the media, it's likely that most climate change skeptics believe humans are a significant cause of climate change. A skeptic may not believe humans cause most or all of climate change yet at the same time think humans contribute significantly to climate change.

It's heartwarming, if not exactly a cause of global warming, to see PolitiFact routinely engaging in behavior that, if performed by a Republican, would warrant something like a "Half True" rating (or worse) on the "Truth-O-Meter."

Clarification Aug. 9, 2014:
Added the word "following" in the midst of the first sentence of the fifth paragraph to clarify intent.

1 comment:

  1. Nice work. You have completely exposed the political bias of PolitiFact, at least in this instance. The 97% figure is completely bogus -- in part for the reasons you give -- yet this figure seems to keep jumping out of nowhere anytime a logical discussion of Global Warming science vs. hoax is attempted.