In 1883, the Indonesian island Krakatoa, home to a massive volcano, seemingly disappeared overnight as an eruption rent the entire island apart, catapulting rock and debris into the atmosphere. For the next few years, as ash circled the entire globe, the average world temperature dropped by several degrees Fahrenheit. Ttherefore, an eruption of similar power in terms of the amount of debris ejected into the atmosphere will likely cause the average temperature around the world to drop by several degrees.
In 1883, the ocean-atmospheric phenomenon La Nina occurred, an event that is always followed by a drop of several degrees in the world's average temperature best challenges the main claim of the argument.