> At least a single volcanic eruption is not enough to change the long-term climate trend, you need a clusters of eruptions to persist through centuries for that.
https://en.m.wikipedia.org/wiki/1883_eruption_of_Krakatoa
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The eruption caused a volcanic winter.[17] In the year following the eruption, average Northern Hemisphere summer temperatures fell by 0.4 °C (0.72 °F).[18] The record rainfall that hit Southern California during the water year from July 1883 to June 1884 – Los Angeles received 970 millimetres (38.18 in) and San Diego 660 millimetres (25.97 in)[19] – has been attributed to the Krakatoa eruption.[20] There was no El Niño during that period as is normal when heavy rain occurs in Southern California,[21] but many scientists doubt that there was a causal relationship.[22]
The eruption injected an unusually large amount of sulfur dioxide (SO2) gas high into the stratosphere, which was subsequently transported by high-level winds all over the planet. This led to a global increase in sulfuric acid (H2SO4) concentration in high-level cirrus clouds. The resulting increase in cloud reflectivity (or albedo) reflected more incoming light from the sun than usual, and cooled the entire planet until the sulfur fell to the ground as acid precipitation.[23]
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Yes, I’m aware of “but many scientists doubt that there was a causal relationship” regarding the rain but the climate has been affected by a single eruption.