The hard part is knowing exactly what will occur because climate is a chaotic system. If a volcano spews co2, this will add a blip to the chart for sure, but it wouldnt equate to a steady rise in co2 over decades, which is what has happened.
50 years is nothing in geological time, which, to me makes it all the more alarming if it is indeed human activity that has driven the increase. Even if humans are 50% to blame, thats still way out of the ordinary and something that should concern us.