Glaciers started melting long before human industrial activity. Glacier dynamics are indeed complex, and melt rates can be influenced strongly by many factors. For example, dark particles of pollution that fall on ice and snow fields can increase melting because they absorb more sunlight than the lighter colored surface. But the vast majority of glaciers across the planet are melting, with the melt rate accelerating in many areas. This global phenomenon can be best explained by research that includes the rise in global temperatures as a main driver. The involvement of other factors does not negate the role of warming temperatures in ice and snow melt.
The National Snow and Ice Data Center tracks changes in glaciers, including where they end (terminus) and how large they are (mass balance) on its State of the Cryosphere site. Their Glacier Photograph Collection provides stark evidence of how rapid the decline is for many glaciers around the world.