You understand that volcanic activity of a very specific sort (large eruptions that inject large amounts of aerosols into the upper atmosphere, preferably in the tropics) is about the only kind that impacts the climate system in a significant way. The most recent eruption of this type was Pinatubo, in 1991. The problem for you is that volcanic events like these *cool* the climate, and only for a few years, at most. We have observed a sustained increase in global average temperature for decades now. Volcanic activity cannot explain that.

El Niño doesn't change the concentration of CO2 - our activities do.