Anyway the amount of co2 that volcanoes emit is quite consistent, but plants and cyanobacterii photosynthetize and make o2 out of it as well as the co2 produced by other organisms gets converted, but the amount we produce due to burning fossil fuels tips this balance, and now there is an 'overflow' of co2, and if it increases the atmospehere's average co2 percentage, it also increases the greenhouse effect and it starts to increase the average temperature of the Earth, but this average increase is misleading as most of the temperature increase is at the poles (>+5°C/+1°C avg.) and the least is at the equator (<+1°C/+1°C avg.), because once some ice starts to melt there, the white snow that reflect most of the sunlight is now water, which is darker, that absorbs most of the sunlight and turns it into heat, which melts more ice, etc.