Sunspots are produced by magnetic activity inside the Sun. The more active the Sun is, the more spots are produced. Observations of sunspots began in 1610 – soon after the telescope was invented – and no other directly obtained data exists from before this time.

Now, Usoskin and co-workers have used the concentration of beryllium-10 in polar ice as a proxy for historic levels of solar activity. Beryllium-10 is produced when cosmic rays interact with particles in the Earth’s atmosphere. The radioisotope then falls to the ground where it is stored in layers of ice. The Sun’s magnetic field can deflect cosmic rays away from the Earth, so a stronger field should lead to less beryllium-10 being produced, and vice versa.

Using modelling techniques, the Finnish team was able to extend data on solar activity back to 850 AD. The researchers found that there has been a sharp increase in the number of sunspots since the beginning of the 20th century. They calculated that the average number was about 30 per year between 850 and 1900, and then increased to 60 between 1900 and 1944, and is now at its highest ever value of 76.

“We need to understand this unprecedented level of activity,” Usoskin told PhysicsWeb. “Is it is a rare event that happens once a millennium - which means that the Sun will return to normal - or is it a new dynamic state that will keep solar activity levels high?” The Finnish-German team also speculates that increased solar activity may be having an effect on the Earth’s climate, but more work is needed to clarify this.