Is global warming caused by humans?
There is little doubt that humans have caused a massive increase in CO2 levels in the atmosphere since the start of the industrial revolution. However there is doubt as to whether this has anything to do with global warming.
The above graph shows that the length of the sunspot cycle (inverted) has a very close correlation to the northern hemisphere temperature fluctuations. Actually the severity of sunspot cycles would be a better measure, but the records are not so consistent as the period because the records were more sparce and the instruments not as good in the 1700s.
It seems then that a decent proportion of global warming is attributable to the Sun and not humanity. This does not mean that we are not having or will not have an effect or that we should be careless.
Another important question is whether global warming will last very long given that an ice age is due any time.