A Cherry Picker’s Guide to Global Temperature Trends

by Chip Knappenberger
October 12, 2009

Accusations of cherry-picking—that is, carefully choosing data to support a particular point—are constantly being hurled around by all sides of the climate change debate. Most recently, accusations of cherry-picking have been levied at analyses describing the recent behavior of global average temperature. Primarily, because claims about what the temperature record says run the gamut from accelerating warming to rapid cooling and everything in between—depending on who you ask and what point they are trying to make.


I am often asked as to what is the “right” answer is. What I can say for certain, is that the recent behavior of global temperatures demonstrates that global warming is occurring at a much slower rate than that projected by the ensemble of climate models, and that global warming is most definitely not accelerating.

Choice of Cherries

But as to questions concerning just how far beneath climate model predictions the rate of warming is, or for just how long the average temperature of the world has not warmed at all, the answers depend on several things, among them the dataset you want to use and the time period over which you examine—i.e., which cherries you wish to pick.





how global temperature trends look across different datasets and choice of starting dates, and which is summarized in the figure above

Each point on the chart represents the trend beginning in September of the year indicated along the x-axis and ending in August 2009. The trends which are statistically significant (p [greater than]0.05) are indicated by filled circles. The zero line (no trend) is indicated by the thin black horizontal line, and the climate model average projected trend is indicated by the thick red horizontal line.

Another use of my Cherry-Pickers Guide besides choosing your own analysis, is to check and see what level of cherry-picking was required to support some statement of the behavior of global temperatures that you saw somewhere.

For instance, in a recent post over at RealClimate.org, Stefan Rahmstorf used about 10-yr to 11-yr trend in the GISS dataset to support the idea that global warming was proceeding pretty much according to plan, concluding “the observed warming over the last decade is 100% consistent with the expected anthropogenic warming trend of 0.2 ºC per decade, superimposed with short-term natural variability.”

A quick check of my Guide would show how carefully Rahmsdorf’s selection was made. Trends a few years longer or a few years shorter that the period selected by Rahmstorf would not have borne out his conclusion with as much conviction.

Another example of careful data selection can be found in recent claims made by Richard Lindzen who is fond of stating that “there has been no statistically significant net global warming for the last fourteen years.” A quick check of my Cherry-Pickers Guide shows Lindzen to be particularly crafty because there is no support for such a statement in any of the five datasets. So how did he arrive at that conclusion? By using annual data values instead of monthly data.


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