The sun, a star at the center of the solar system, is the furnace that sends energy to planet Earth and makes all life possible. Without it, earth would be a barren, icy stone, traveling through the darkness of space. The sun has no truly solid surface, but is instead a large ball of extremely hot gas in which many chemical and nuclear reactions are continuously taking place. Even though it is not solid, it does have a structure composed of layers. Composed mostly of hydrogen and helium, its temperatures and pressures increase as its core, or center, is reached. The photosphere is the layer just below the sun’s atmosphere, and it is also the layer of the sun that is seen from earth.
The hot, gaseous material of the sun is in constant motion. This motion creates a dynamic magnetic field. Sunspots are created at the points where the magnetic field lines pierce through the photosphere. To a viewer on Earth, the spots appear to be dark, and they are, in fact, cooler than the rest of the photosphere. But on the sun, the word “cool” is relative. The temperature of sunspots is around 3,500 degrees Kelvin. Sunspot activity rises and falls in a cycle of about 11 years. At the low point, or minimum, of the cycle, there are few sunspots. During the high point, or solar maximum, the highest number of sunspots is seen.
Scientists and astronomers have been able to track these sunspot cycles in nature by direct observation, by observing ancient sediments in the outback of Australia and also by using data from glaciers. Over the long term, years with more sunspot activity tend to be hotter than those with little or none. In fact, there have been small “ice ages” during cycle minimums, such as the famous Maunder Minimum.
Since sunspot areas are cooler than the rest of the sun’s photosphere, it may seem intuitively difficult to accept that years during which there is more sunspot activity are hotter. But it is the areas where sunspots occur that are most likely to produce coronal mass ejections, or CMEs. These “solar flares” can heat the gases of the sun’s corona (the part that is seen during a solar eclipse) to 20 million degrees Kelvin or even higher. Medium- to large-size solar flares can trigger radio blackouts and can also interfere with satellite activity.
In addition to radio and satellite interference, it has also been thought that the activity of sunspots can affect agricultural production and crop yields. A study done by the Economic Research Service of the U.S. Department of Agriculture showed that: 1. Lower than average crop yields are associated with low sunspot activity, 2. Higher than average yields are associated with high sunspot activity and 3. Both the single and double sunspot cycles may give useful information in predictions of yield deviations. (A double sunspot cycle is one that contains two single cycles.) The study examined the relationship between crop yields and sunspot activity for wheat in Texas and Kansas, corn in Illinois and Nebraska, rice in Louisiana and cotton in Texas. Data for wheat, corn and cotton were from 1866-1973. Data for rice were from 1895-1972.
William Stanley Jevons, a British economist (1835-1882), suggested that there was a relationship between sunspots and crises in business cycles. He reasoned that since sunspots affect Earth’s weather, they then affect crop yields and, therefore, the economy. Jevon’s reasoning has been called the “sunspot theory.” Citing English agricultural price data from the years 1259-1400, Jevons observed that there appeared to be a consistent trend in prices of various agricultural products over the 11-year solar activity cycles. More modern data suggest that, even though there are many and complex variables that determine food production and prices, there is still an underlying association between food prices and the solar cycle.
Dr. Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics has also done extensive research on the subject of the sun’s effects on Earth’s climate. She concludes that although the sun’s brightness changes only slightly with the solar cycles, the indirect effects of increased solar activity may still greatly magnify the sun’s effect on Earth’s temperatures. Change in temperature, in turn, has an effect on the production of crops.