Since the mid 20th century, the warming trend is virtually 100% attributable to human activity. As has been noted many times, proof is the domain of mathematics and spirits, not science. Science can only rely on evidence to make conclusions.

This shouldn't be such a difficult thing to understand. Climate science is quite familiar with the array of factors influencing climate, both natural and anthropogenic. Attribution of warming or cooling for any period relies on a comprehensive analysis of all of the factors acting upon the climate over that period. We look at solar activity, volcanism and albedo changes, teleconnections and ocean current changes, land use impacts and carbon cycle changes, changes in atmospheric composition, and more. Several such analyses have found that the anthropogenic warming contribution since the mid 20th century is actually over 100% with natural and some anthropogenic factors yielding offsetting cooling. That's simply what all of the evidence points to.