By David L. Brown
What is wrong with this picture? It is our Sun, as photographed a few days ago. And what is wrong is that it shows no sign of sunspots, none at all. And that is a cause for curiosity because the low point in the usual 11 year sunspot cycle was supposed to have ended well over a year ago, and yet for day after day, week after week, month after month the Sun continues to present a blank, featureless face to the Universe. The return of spots to the surface of the Sun is now about 18 months past due.
Scientists do not have an explanation for this, but there are historic precedents. During the 17th and 18th Centuries the Sun entered an extended period of quiescence during which virtually no sunspots were observed. Dubbed the Maunder Minimum, the anomalous period lasted from about 1645 to 1715.
Does this mean anything to we humans here on Earth? After all, what difference could it make whether the Sun exhibits spots or appears like a featureless orange ball? Well, it could mean a lot. Many climate scientists relate the Maunder Minimum and other periods of low activity on the Sun with cooling. In fact, the event called the Little Ice Age appeared to be connected in time with the Maunder Minimum, suggesting a correlation between the two.
To understand just how unusual the Maunder Minimum was, during one 30-year period of the event astronomers observed only about 50 sunspots. In modern times, 40,000–50,000 spots would have been observed during that length of time. That represents a reduction on the order of a thousandfold.
Now you may have learned that sunspots are cool eruptions on the surface of the solar disc, so at first glance it may seem that more sunspots, not fewer, would result in cooling. But the areas around a sun spot are hotter than the average surface temperature of the Sun, resulting in a higher total output of radiation.
Below is a graph that shows the relative sun spot activity over time, including the Maunder Minimum. It is interesting to note that spot activity was considerably lower during the years before and after the Minimum, suggesting that the actual event may have lasted for nearly 150 years. Note, too, that there have been other, less severe reductions in solar output, one around 1800 termed the Dalton Minimum and another milder but more extended period centered on about 1900. If there is any periodic system at work here, we may be due for another such period, and the blank face the Sun is showing us now hints that could be the case.
If it is true that reduced solar activity can result in cooling of the Earth, and if we are actually entering a new period of minimum activity, we human beings may be getting the benefit of an amazing stroke of luck. Just as greenhouse gas is raising the average temperature of the planet, it may just be possible that the Sun is turning down the thermostat. We may not experience a new Little Ice Age, but it could offset the possibility of a severe heating event due to greenhouse gas.
Whether or not this is truly the beginning of a significant solar minimum is uncertain, but scientists are puzzled by the fact that a new cycle of spots has failed to appear as predicted. Certainly, something is going on and it may just give us time to bring greenhouse gas under control and avoid the danger of runaway climate change. This is something to keep an eye on.