Now I hesitate to jump into this one, but there are a couple of inaccuracies here.
First, the problem of CO2 in the atmosphere is that it continues to raise the radiative forcing the more you add, although there is a good argument that at about 550-600ppm (parts per million) the effect is exhausted (some claim that is already the case). That means that the more CO2, the more the atmosphere warms. The rule of thumb is that for a doubling of CO2 from pre-industrial levels of 280ppm to 560ppm, the direct forcing increases by something in the order of 1-2 degrees C. The catastrophic bit comes from positive feedbacks which increase the effect to something like between 2 and 5 degrees C. That is, the atmosphere could warm by as much as 5 C on average for a CO2 level of 560ppm.
However more recent estimates suggest direct forcing might be closer to 1.2 C or less, and feedbacks are currently not well quantified. It is possible feedbacks are net negative.
The reason that we need to reduce CO2 emissions is that we haven't yet doubled CO2 from pre-industrial levels. We are currently at something like 410-420ppm I believe. Well short of the 560ppm a doubling would mean. Keeping CO2 levels to not much more than we are currently at would mean, according to the science, an average increase of less than 2C. That is, if we keep CO2 from increasing by too much more, we might avert catastrophic global warming.
So according to the science, we still need to reduce CO2 emissions.
As for volcanoes, as best we know they emit on average less than 1 billion tonnes of CO2 per annum. Humans produce something like 30 billion tonnes of CO2 per annum.
The optional RM125B swingarm issue is significantly more complicated...
