evidence: The Sun has an 11-year geomagnetic cycle. From the peak to the minimum, the average amount of energy reaching the top of Earth’s atmosphere varies by about 0.1%. It’s a small difference: in an average cycle, it’s only enough to warm or cool Earth’s surface temperature by approximately 0.05 degrees Celsius. (There also appears to have been a small, long-term increase in solar activity in the early twentieth century, which added to the human-caused global warming trend during that period).