The mechanism and even the existence of the Atlantic Multidecadal Oscillation (AMO) have remained under debate among climate researchers, and the same applies to general temperature oscillations of a 60-90-year period. The objective of this study is to show that these temperature oscillations are real and not artifacts and that these oscillations have different external cosmic origins. The authors have studied how well the variations of astronomical harmonic resonances (AHR) could explain the 60-year temperature variations, which are based on instrumental records and the tree-ring data of the supra-long Scots pine tree-ring record for northern Finnish Lapland (subsequently called the Finnish timberline pine chronology (FTPC)), stretching to the year 5634 BC. Powerful volcanic eruptions have significant temperature-decreasing impacts, and they are the major disturbances to eliminate in analysis. The similarities between the temperatures of the tree-ring trend and the AHR trend are easy to observe even by the naked eye. The statistical analysis shows that these two signals are statistically related. The analyses also show that the well-known Gleissberg cycle of 80-90 years is the dominating cycle caused by the Suns’ activity changes but the observed 60-year cycle can be connected to the AHR cyclicity.