As near certain as makes no difference. It's certain that we have increased the CO2 and other greenhouse gases in the atmosphere and there is a lot of research to show that these gases should increase world temperatures and climate variability. It's certain that world temperatures are increasing and that the climate has become more variable and that these changes are correlated with the increase in CO2.
Since there are no other plausible mechanisms that have not been refuted it's perverse to think that we haven't created the problem. This is an almost universal view amongst those, such as the IPCC members, who've studied the subject.