On the alleged coherence between the global temperature and the sun׳s movement

• The global temperature and the movement of the solar system center are compared.
• Scafetta claims coherence at at least 4 periods.
• This paper points out some flaws in the analysis due to lack of time-invariance.
• Under certain conditions only a weak coherence at a period of 15–17 years is found.
• The lack of a physical model makes it doubtful whether this is significant.

It has recently been claimed that there is significant coherence between the spectral peaks of the global temperature series over the last 160 years and those of the speed of the solar center of mass at periods of 10–10.5, 20–21, 30 and 60–62 years. Here it is shown that these claims are based on a comparison between spectral peaks in spectral estimates that assume that the global temperature data contains time-invariant spectral lines. However, time–frequency analysis using both windowed periodograms and the maximum entropy method shows that this is not the case. An estimate of the magnitude squared coherence shows instead that under certain conditions only coherence at a period of 15–17 years can be found in the data. As this result builds on a low number of independent averages and also is unwarranted from any physical model it is doubtful whether it is significant.