Professor Ian Plimer says...
The volcanic ash emitted into the Earth's atmosphere in just four days - yes - FOUR DAYS ONLY by that volcano in Iceland, has totally erased every single effort you have made to reduce the evil beast, carbon. And there are around 200 active volcanoes on the planet spewing out this crud any one time - EVERY DAY.
However, I noted this passage from the following website...
Anti-global heating claims – a reasonably thorough debunking | Scholars and Rogues
Volcanoes emit a lot of gases, including significant amounts of CO2. Unfortunately, according to papers from back in the late 1990s, “Volcanoes contribute about 110 million tons of carbon dioxide per year while man’s activities contribute about 10 billion tons per year.”
This means that anthropogenic CO2 emissions are 100x greater than volcanic CO2 emissions.
In addition, volcanoes generally cause global cooling through the emissions of cloud-forming sulfur dioxide and water-cycle feedback.