Monday, October 26, 2009

Skeptical about global warming skeptics

Ordinarily I avoid anything published by AssPress like the proverbial plague. However, this article on global warming skeptics is actually worth the bother:
Have you heard that the world is now cooling instead of warming? You may have seen some news reports on the Internet or heard about it from a provocative new book.

Only one problem: It's not true, according to an analysis of the numbers done by several independent statisticians for The Associated Press.


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.


The AP sent expert statisticians NOAA's year-to-year ground temperature changes over 130 years and the 30 years of satellite-measured temperatures preferred by skeptics and gathered by scientists at the University of Alabama in Huntsville.

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."

The chatter from global warming skeptics, who contend that we're actually now cooling, has heated up considerably since the release of Super Freakonomics. Actually, these climate contrarians give us an inadvertent lesson in how to lie with statistics, as the article describes:

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.

I've discussed previously some important facts about climate data that need to be kept in mind, including the fact that climatic data is noisy. By that, I mean that there tends to be a great deal of variability in the yearly numbers, making it more challenging to ascertain long-term trends. Even with all the noise, however, one can notice that there has been a very distinct trend over numerous decades, and that trend is upward. Oh, and since we're now in an El Niño pattern, there's a decent chance that 2010 will easily compete with 1998 and 2005 for the title of warmest year on record.

Note that the graphic above was courtesy of Matthew Yglesias.

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