Since the 1990s, the erroneous conception has spread that sunspots were the main cause of current global warming and that the introduction of significant quantities of greenhouse gases into the atmosphere by man instead had a marginal role.
This theory, initially proposed by Friis-Christenses and Lassen, correlated the duration of the solar cycle with the Earth's climate and, in particular, with current global warming.
This theory, however, was denied at the end of a heated and long scientific debate triggered by Dr.
Peter Laut, who demonstrated through scientific publications that the data produced by Friis Christensen and Lassen in support of the theory had been artificially packaged and manipulated to derive fallacious conclusions.
Laut's rigorous analysis of the data called into question by the authors showed that the data not only was unable to support the theory, but proved its fallacy. The falsification of Friis Christensens and Lassen's theory has received broad consensus from the scientific community and it is now clear that human activities are the main cause of current global warming.
But what are sunspots?
Sunspots can be observed rather easily, a small telescope used with the eyepiece projection method is sufficient. In some circumstances, especially at dawn and dusk, moments when the brightness with which the Sun appears from the Earth is minimal, sunspots can also be seen with eye.
However, it is best to never look at the Sun without the aid of a filter as it can cause permanent damage to the retina. A sunspot is a region of the Sun's surface that is distinct from its surroundings by a lower temperature and strong magnetic activity.
Even if in reality the sunspots are extremely bright, because they have a temperature of around 4000 kelvin, the contrast in thermal emissivity compared to the surrounding regions, even brighter thanks to a temperature of 6000 kelvin, makes them clearly visible as dark spots.
Numerous similar spots have also been observed in stars other than the Sun, and they take the more general name of stellar spots. Today, many different periods of variation in the number of spots are known, of which 11 years is simply the most obvious.
The same period is observed in most other expressions of solar activity, and is deeply linked to variations in the solar magnetic field. It is not known whether very long period, because the interval recorded by astronomers is too short, but their existence is strongly suspected.