Ecosystem fail.
Volcanic activity changes over the course of thousands of years. Point being - it doesn't matter how much CO2 volcanoes spew into the atmosphere; relative to the scope of human lifetimes the environment has reached perfect equilibrium. Every year the amount of CO2 generated by volcanoes is perfectly offset by that removed through natural processes.
It wouldn't matter if human CO2 contributions were only 1/1000th of that emitted by volcanoes (in reality it is much higher), the point is that in the past 30 years alone CO2 concentrations have gone up 11%, which is colossal when you consider the fact that such changes usually require thousands of years.
The danger isn't in "how much" we disrupt the environment, it's how quickly we're throwing delicate natural cycles out of equilibrium, and as much as everyone likes to talk about cycles, which do change over time in natural and periodic ways, they forget that these cycles reciprocate over the course of several thousand years, never over the course of one century.
Despite this, climate change doesn't really concern me as much as how lavishly we waste our resources. Basic metals like aluminum, copper, tin are all reaching the points of diminishing returns in mining, with economical mining of copper, perhaps the most important metal in the manufacture of all electronic goods, expected to end within decades. If the global rate of consumption continues along this path, climate change will be a small worry.