The sun is so important to the earth, it seems reasonable to suspect solar activity as the cause of warming or cooling of the planet.
Sunspots and Solar Activity
A German Named Heinrich Schwabe in the early 19th century was convinced there was a planet between Mercury and the sun, named Vulcan no less, and spent some time trying to find it. Alas, no planet. (Sorry Spock). What he did find were sunspots, dark areas on the sun’s surface that seemed to appear cyclical.
Later observations showed they are magnetic events that occur on roughly eleven year cycles and are, indeed, associated with increased solar flare activity. These increases in solar activity have been correlated with slight increases in global temperatures - but only small cyclic changes.
We have had other cyclic occurrences of cooling that are not completely understood, but solar activity as well as variances in the earth’s orbit, and axis tilt of the earth seem come together in rough patterns and be responsible for small temperature changes.
This is not happening now.
Interestingly, since 1975 during the time we have seen the sharpest increases in global temperature, the sun has had slightly less than average activity. Bottom line, the upward trend in temperature is not due to sun spots or solar activity.
Layers of the Atmosphere Warming Differently
Even more convincing of the sun’s lack of culpability are is the distribution of heat in layers of the atmosphere.
Our atmosphere is a bit like a layer cake without the frosting. We hang out in the troposphere along with everybody else, clouds, weather, airplanes and Mt. Everest. It is here where carbon dioxide and other greenhouse gases collect. The next layer up is called the stratosphere. If the warming was due to the increased solar activity, there should be warming at all levels.
In fact, the stratosphere is cooling, which is exactly what we would expect if the warming was due to trapped CO2 in the troposphere. As the heat builds up in the bottom layer, the next layer up does not get its “fair share” of infrared radiation, and cools. We are seeing exactly this.
Fluctuation of Warming
One more point. If the sun was the “bad guy” here, we would expect to see increased warming during the day and summer. In fact, it is the other way around. There are larger increases in temperatures at night and during the winter, which is consistent with climate change models.
Conclusion—variances in sun output can account for small variances in temperature, of a cyclic nature. We cannot blame the upward march of global temperatures on the sun.