A hypothesis must be falsifiable for it to be valid in the first place, and saying "the Sun did it" is a valid way to falsify the hypothesis; thus you now must also prove the Sun is not affecting climate change to the degree that we have measured.
No one has been able to prove this, and all evidence collected by NASA seems to indicate that the Sun is by far the largest driver of climate fluctuations on Earth, even during the modern age, not humans.