The Sun’s activity follows a cycle that lasts about 11 years, along which the number of sunspots on the surface of our star decreases to a minimum, and then grows, reaching a peak. The last solar maximum dates back to 2013, and is preparing to return this year. What will this mean for the planet? There are those who claim that it is one of the main phenomena that influence the earth’s climate, but this is not really the case. Or rather, perhaps it was in the past, before the greenhouse effect produced by human activities supplanted it as the main driver of climate change. Let’s see what we know about it.
Solar cycles
The solar cycle, as we were saying, is the rhythm that describes the periodic trend of solar activity, based on the greater or lesser presence of sunspots on the surface of the Sun, produced in turn by the greater or lesser magnetic activity within our star. When the Sun has a greater number of spots, activity increases, as does the energy that is emitted into space. And with more energy radiated towards our planet, temperatures on Earth are obviously also set to rise at the peak of the solar cycle. On average, the difference between the energy emitted during the maximum and minimum of the solar cycle is not much, just 0.1% more. But even so, the effect on Earth can be more than concrete.
Climate and solar storms
During periods of maximum activity of the Sun, the solar winds, the stream of charged particles emitted by the star, become more intense. As well as solar flares, coronal mass ejections, and all phenomena related to so-called space weather. In turn, solar winds, cosmic rays, geomagnetic storms, influence the Earth’s atmosphere in many ways, produce wonderful spectacles such as the aurora borealis, can influence the functioning of satellites and electronic devices, induce the formation of clouds and other meteorological phenomena. The effects of all this on the climate are certainly not negligible, although difficult to model and predict.
A case that is often cited to show the possible effects of solar cycles on the Earth’s climate is that of the so-called Little Ice Age, a period that goes more or less from the mid-fourteenth century to the mid-nineteenth century, during which there was a significant decrease of average temperatures, at least in some areas of our planet. Coincidentally, at its peak, between 1645 and 1715, another peculiar phenomenon was also catalogued, called the Maunder minimum: a period of minimal solar activity, in which sunspots almost disappeared. Another similar period, called the Spörer minimum, is believed to have occurred between 1460 and 1550, also in this case a time interval in which the available information speaks of particularly cold temperatures, at least in Northern Europe.
What effect on the climate?
Coincidences such as those just mentioned lead us to hypothesize that the influence of the periods of maximum and minimum solar activity on the Earth’s climate may also prove particularly intense. And if it can cool the planet during extremely weak solar cycles, it can also warm it during intense cycles. The most recent estimates say that the peak of the current solar cycle, cycle 25 (since measurements began in 1755), should arrive this year. And therefore someone will inevitably be tempted to attribute the record temperatures expected for this 2024 to solar activity (almost certain given the trend of recent years and the coincidence with the El Nino phenomenon, which began last year and is destined to become more intense in the coming months ).
The majority of the scientific community, however, believes that the effects of solar activity on the climate of our planet, although indubitable, have long since been eclipsed by those of anthropogenic global warming, which are much more intense and rapid. It is no coincidence that the last solar cycle, the 24th which ended in December 2019, was the fourth weakest ever recorded, and despite this the average temperatures of our planet continued to rise inexorably. The current cycle 25 is also not expected to be particularly intense, with the most recent forecasts from the US National Oceanic and Atmospheric Administration placing it below the average of the last 300 years. If even in 2024 we will see the dramatic temperature records to which we have become accustomed in recent years, in short, remember that the Sun is certainly not to blame.