In 1645 marked the beginning of the Maunder Minimum, a period of significantly low solar activity. This event coincided with the so-called “Little Ice Age” a period of cooler temperatures across the North Atlantic that led to harsher winters and shorter summers in Europe. While it may be a mere coincidence, astronomers and geologists have concluded that the relationship between the Sun and Earth plays a significant role in our planet’s climate.
Sun and Sunspots
During a typical 22-year period, consisting of a couple of solar cycles, there are between 30,000 to 40,000 sunspots. However, during a part of the Maunder Minimum, precisely at the end of the 17th century, sunspots were at zero. Scientists are still unsure of what caused the Maunder Minimum, which ended in 1715. But they do know that it overlapped with the Little Ice Age. The overlap might just be a coincidence. After all, this colder period began before and lasted beyond the Maunder Minimum. Moreover, the rest of the planet seemed unaffected.
However, the number of sunspots is correlated with the overall brightness of the Sun. So, during the Maunder Minimum, the Sun was slightly less intense, and the northern latitudes of the Earth are more sensitive to even minor changes in solar output. The northern hemisphere has more land surface, and land changes temperature much more rapidly than water. Since higher latitudes experience more pronounced seasons, small solar changes can have cascading effects that wouldn’t occur across the rest of the globe.
There is still no consensus on the link between the Maunder Minimum and the Little Ice Age. But when we expand the geological timescale, we find an unexpected but very strong correlation. The first person to highlight the Earth-Sun system’s effect on climate was the physicist and astronomer Milutin Milankovitch. In the 1920s, the Serbian scientist discovered various natural cycles in Earth’s orbit that could be responsible for significant climate changes.
Natural Earth-Sun Cycles
First natural cycle concerns Earth’s orbit, which slowly changes from elliptical to circular and back every 100,000 years. These changes are due to slight gravitational tugs from Jupiter and Saturn. Currently, Earth’s eccentricity has a value of 0.0167 and is decreasing. These orbit changes influence the duration and amplitude of the seasons. When Earth is farthest from the Sun, it moves more slowly compared to when it’s closest to the Sun. So, if Earth is at maximum eccentricity, and the farthest point of Earth aligns with the northern hemisphere’s summer, that year’s summer will last longer than usual.
Another cycle modifies our planet’s axial tilt from 22.1° to about 24.5° degrees every 41,000 years. Earth’s current tilt is 23.44° degrees and decreasing. This cycle also affects the extent of the seasons. Greater tilt means more time exposed to direct sunlight or more time hidden from the Sun, making the seasons more extreme.
A third cycle is known as axial precession. Our planet wobbles like a spinning top every 25,700 years, with Earth’s rotation axis drawing a circle in the sky. This changes which hemisphere receives more sunlight. Currently, the point of closest approach of Earth to the Sun appears to align with the southern hemisphere’s summers. These cycles interact with each other, sometimes reinforcing or canceling each other out. But whatever happens, Earth ‘s position relative to the Sun has a significant influence on our planet’s climate.
Anthropogenic Climate Change
Comparisons of Milankovitch cycles with temperature records from ice core samples reveal a very close connection. Ice age periods align with Milankovitch cycle periods when Earth, at northern latitudes, receives less sunlight than usual. Warm periods align with more sunlight received in the North. The last ice age occurred about 12,000 years ago, which coincided with a slight increase in overall sunlight due to Milankovitch cycles.
The change led to the extinction of many species, such as woolly mammoths, directly followed by the small change in our planet’s orbital configuration. According to Milankovitch cycles, Earth should actually be entering a cooling period right now. However, the consequences of greenhouse gas emissions have completely overshadowed the relationship between the Sun and Earth. So, once again, the climate change we are experiencing is not a natural phenomenon but solely and exclusively anthropogenic.