In September 2020, scientists announced that a solar minimum had occurred in December 2019, marking the end of Solar Cycle 24 and the commencement of Solar Cycle 25, meaning that stargazers can expect to see an increase in solar activity. But as our sun wakes from a period of relative inactivity, how will this new solar cycle affect life on Earth?

According to NASA, a solar cycle is “the cycle that the Sun’s magnetic field goes through approximately every 11 years.” The sun is essentially a giant ball of electronically charged gases. The movement of these charged gases generates a magnetic field around the sun with north and south poles. Over 11 years, the poles switch position; with north becoming south and vice versa. This is known as a solar cycle, with the switching of poles occurring during the peak of each cycle (solar maximum). While scientists do not yet fully understand the mechanism which causes the poles to switch, they are able to track the cycle by observing the number of sunspots present on the sun’s surface.

According to the European Space Agency (ESA), a new solar cycle commences when “new spots emerging at mid-latitudes on the Sun’s surface are opposite in magnetic polarity than the sunspots from the previous cycle.” However, due to the variability of the sun, it can take months for scientists to declare that an event has occurred. The exact length of each solar cycle fluctuates and can range from between 9 – 14 years. Frédéric Clette, the director of the World Data Center for the Sunspot Index and Long-term Solar Observations at the Royal Observatory of Belgium explained that, “It is only by tracking the general trend over many months that we can determine the tipping point between two cycles.” 

During September 2020, scientists from the Solar Cycle 25 Prediction Panel – an expert panel co-sponsored by NASA and the National Oceanic and Atmospheric Administration (NOAA) – announced that a solar minimum occurred in December 2019. A solar minimum indicates the beginning of a new solar cycle. 

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How Does Solar Activity Affect Earth?

Sunspots usually exist in pairs that have magnetic fields which point in opposite directions. The magnetic field of a sunspot is about 2 500 times the strength of Earth’s magnetic field and is much stronger than anywhere else on the sun. In the area between these two opposing magnetic fields, solar flares usually occur. These are extremely large explosions that can emit as much energy as a billion megatons of TNT. 

The radiation is usually emitted in the X-ray and ultraviolet (UV) portion of the electromagnetic spectrum. The emitted radiation and magnetic fields cause geomagnetic storms which can significantly alter the upper layers of Earth’s atmosphere. During periods of active sunspots, the Earth will experience more geomagnetic storms, which causes an increase in Aurora Borealis and Aurora Australis. Geomagnetic storms can damage satellites and, if they are particularly strong, can cause blackouts on power grids and disrupt radio communications. These storms can expose astronauts to harmful doses of radiation and could potentially interfere with future missions to the moon or Mars. 

However, these storms do not occur without warning. Sunspots forming below the surface of the sun create dark patterns across the surface. While solar storms cannot be stopped, advanced warning does give operators of satellites, telecommunication systems and power grids, as well as astronauts, time to prepare. 

There is still debate within the scientific community as to the extent of the effects of the sun’s cycle on Earth’s climate. The most apparent example of the sun’s cycle affecting Earth’s climate occurred during 1645-1715 when the sun went through a period of near-zero sunspot activity. During this period of sunspot minima (The Maunder Minimum) much of Europe and North America experienced an extremely cold spell, known as the “Little Ice Age.” However, although the Little Ice Age occurred during an extended period of sunspot minima, this is not conclusive proof that the cycle of the sun affects the climate on Earth. Distilling the effects of the sun from the other numerous uncontrollable and complex variables (such as the interactions between land, oceans and atmosphere) is a near impossible task. For example, there is evidence that The Maunder Minimum occurred during a time of large volcanic eruptions. Debris from large volcanic eruptions is known to reduce the amount of solar radiation that reaches Earth, which could be a contributing factor which resulted in the Little Ice Age. 

Scientists have determined that there are small changes to the total amount of solar irradiation that reaches Earth based on the stage of the sun’s cycle. During periods of solar maximum, there is a substantial increase in the incident solar UV, which primarily affects Earth’s stratosphere. 

Scientists at NASA have conducted climate model experiments in an attempt to better understand the effects of the sunspot cycle on Earth’s climate. Their models found that the increase in incident solar UV during solar maximum conditions can influence tropospheric rainfall patterns in a way that is consistent with some field observations. Periods of increased solar activity favoured rainfall north of the equator and decreased rainfall near the equator and at northern mid-latitudes. However, the effects of the increased solar activity only favoured an increase in the likelihood of these events, and the influence appears to have been modified by global warming, thus the effectiveness may change over time.

Although the changes in total solar irradiance that Earth receives during the sun’s cycle are small, these changes do appear to increase sea surface temperatures. This effect is most apparent at latitudes where there is minimal cloud cover and irradiance is abundant. An example of such an area is the Northern Hemisphere subtropics during summer. According to NASA, the increase in sea surface temperature can increase circulations spiralling away from the subtropics. This will also favour reduced rainfall near the equator, the northern mid-latitudes, and to the south. Thus, both the increase in incident solar UV and the increase in total solar irradiation appear to have similar effects. Yet again however, it is important to remember that none of these processes occur in isolation, and given the complexity of the different affecting forces, it is almost impossible to draw a definitive conclusion as to the effect of the solar cycle on Earth’s weather and climate. 

Solar Cycle 25 Predictions 

Solar Cycle 24 was the weakest cycle in the last 100 years and formed part of a trend of declining solar cycle amplitude that began in Solar Cycle 21. Solar Cycle 24’s maximum occurred during April 2014, with the number of sunspots peaking at 114, which is well below the average of 179. 

The Prediction Panel believes that Solar Cycle 25 will break the trend of decreasing solar cycle amplitude seen over the last four cycles and predict that the maximum number of sunspots will occur in July 2025 and will peak at 115. Although Solar Cycle 25 is not predicted to be weaker than Solar Cycle 24, it is predicted to be weaker than average. 

Predicting the cycle of the sun is much like predicting the path of a hurricane. Scientists use numerous models and mathematical equations to assist in the predictions. Over the past 40 years, the computer equations used to model the sun’s activity have become more adept at predicting the solar cycles. However, as the mechanisms behind the magnetic switch are still not fully understood, the sun does manage to surprise scientists. 

Interestingly, there is a group of scientists that disagree with the predictions released by the Solar Cycle 25 Prediction Panel. A research team led by prominent astrophysicist Scott McIntosh at the National Center for Atmospheric Research (NCAR), believe that Solar Cycle 25 maximum sunspots will peak between 210 and 260, making it one of the strongest cycles ever observed. The team’s predictions are based on a theory which suggests that the sun has overlapping 22-year magnetic cycles which interact and produce the 11-year sunspot cycle as a byproduct. 

McIntosh explained that, “Scientists have struggled to predict both the length and the strength of sunspot cycles because we lack a fundamental understanding of the mechanism that drives the cycle.” He believes that if their forecast proves to be correct, it will support the framework of their understanding of the Sun’s internal magnetic machine.

Irrespective of whose predictions you choose to believe, Solar Cycle 25 is underway, and there is nothing that we on Earth can do to stop that. While scientists work hard to better predict the solar cycle, the reality is that the predictions allow for better preparations, but whether the solar cycle is of a high or low intensity is completely out of humanity’s control.