The sun is not constant, but is very cyclic and predictable. They also monitor the sun closely, so they know that is NOT the cause of global warming.
{...
The
solar cycle or
solar magnetic activity cycle is a nearly periodic 11-year change in the
Sun's activity measured in terms of variations in the number of observed
sunspots on the solar surface. Sunspots have been observed since the early 17th century and the sunspot time series is the longest continuously observed (recorded) time series of any natural phenomena.
The magnetic field of the Sun flips during each solar cycle, with the flip occurring when sunspot cycle is near its maximum. Levels of
solar radiation and ejection of solar material, the number and size of
sunspots,
solar flares, and
coronal loops all exhibit a synchronized fluctuation, from active to quiet to active again, with a period of 11 years.
This cycle has been observed for centuries by changes in the Sun's appearance and by terrestrial phenomena such as
auroras. Solar activity, driven both by the sunspot cycle and transient aperiodic processes govern the environment of the Solar System planets by creating space weather and impact space- and ground-based technologies as well as the Earth's atmosphere and also possibly climate fluctuations on scales of centuries and longer.
Understanding and predicting the sunspot cycle remains one of the grand challenges in astrophysics with major ramifications for space science and the understanding of magnetohydrodynamic phenomena elsewhere in the Universe.
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