Solar activity is the main cause of global warming

Myth:

Recent temperature rises have been caused by solar activity, not increases in CO₂.

Fact:

Solar radiation reaching the Earth (known as insolation) can only result in minor temperature changes. The sun’s energy fluctuates on an 11-year cycle. It only changes by about 0.1 percent each cycle, so its impact is very small. 

Scientists estimate that solar activity has contributed about 0.1°C to temperature increases since 1870. For the last three decades solar activity has actually been decreasing, yet the planet isn’t cooling. If CO₂ levels had no impact on global temperatures, as climate sceptics claim, then you would expect this not to be the case. What is actually happening is that the impact of CO₂ emissions is overwhelming any cooling effect from decreased insolation. Of course, when solar activity starts to increase again, it will exacerbate the impact of greenhouse gas emissions. 

Another important factor is that if solar activity were causing recent temperature increases, the atmosphere would warm uniformly. In fact, the upper atmosphere (above 20 kms) is cooling, while the lower atmosphere is warming. This is not consistent with solar activity. It is consistent with increases in CO₂, however. In addition, if solar activity were the cause of recent warming, summers would be warming more than winters, and days more than nights. In actuality, neither of these things is happening. 

Hence, all the evidence suggests that CO₂ is the cause of the warming we are currently experiencing.

Graph showing the disconnect between solar activity and global temperatures over the past half century. [Source: Sceptical Science

Sources:

NASA, “Is the Sun causing global warming?” https://science.nasa.gov/climate-change/faq/is-the-sun-causing-global-warming/

David Herring, “Couldn’t the Sun be the cause of global warming?” US National Oceanic and Atmospheric Administration, 29/10/20

Centre for Science Education, “The Sun and Climate Change,” University Corporation for Atmospheric Research. https://scied.ucar.edu/learning-zone/sun-space-weather/sun-and-climate-change  

“Sun & climate: moving in opposite directions,” Skeptical Science. https://skepticalscience.com/print.php?r=8