Climate disruption deniers have been claiming for years now that the global temperature has been cooling down, even though the temperature data clearly shows that it isn’t. Scientists and statisticians have pointed out that, mathematically speaking, the recent reduced warming trend is well within the noise, or put another way, it’s weather, not climate.
A new report by the Associated Press reveals what many of us knew already – the denier’s claims don’t hold water, statistically speaking. The report is intriguing because the AP provided their data to four independent statisticians without telling them what it was, and all four found that the slower warming of the past decade was statistically insignificant with respect to the actual data.
In a blind test, the AP gave temperature data to four independent statisticians and asked them to look for trends, without telling them what the numbers represented. The experts found no true temperature declines over time.
“If you look at the data and sort of cherry-pick a micro-trend within a bigger trend, that technique is particularly suspect,” said John Grego, a professor of statistics at the University of South Carolina.
Furthermore, the data that the AP sent to the statistician came from two different sources – the National Climate Data Center (NCDC), run by NOAA, and the satellite data preferred by climate disruption deniers that is generated by scientists John Christy and Roy Spencer from the University of Alabama in Huntsville. In both cases, the statisticians found no statistically significant trends over the last ten years.
Statisticians who analyzed the data found a distinct decades-long upward trend in the numbers, but could not find a significant drop in the past 10 years in either data set. The ups and downs during the last decade repeat random variability in data as far back as 1880.
Saying there’s a downward trend since 1998 is not scientifically legitimate, said David Peterson, a retired Duke University statistics professor and one of those analyzing the numbers.
Identifying a downward trend is a case of “people coming at the data with preconceived notions,” said Peterson, author of the book “Why Did They Do That? An Introduction to Forensic Decision Analysis.” (emphasis mine)
The AP interviewed Don Easterbrook, who claimed that “We started the cooling trend after 1998. You’re going to get a different line depending on which year you choose.” According to one of the statisticians, the fact that you have to choose 1998 as your starting point in order to observe a (statistically insignificant) cooling trend is part of the problem.
Grego produced three charts to show how choosing a starting date can alter perceptions. Using the skeptics’ satellite data beginning in 1998, there is a “mild downward trend,” he said. But doing that is “deceptive.”
The trend disappears if the analysis starts in 1997. And it trends upward if you begin in 1999, he said.
This is what’s referred to in statistics as “endpoint sensitivity,” and it’s the main reason that climate disruption deniers like Easterbrook can appear and sound so reasonable when they’re actually misusing or misunderstanding the data.
