The problem of CO2 has been known and warned about for decades. The changes that are already being seen are coming in at the upper end of IPCC predictions and as has been said there are possible tipping points that will accelerate change.
I saw recently that effects on the Polar Vortex are such that they will be deeper and last longer so that there will be worse cold spells as well as worse hot spells.
Then regardless of human-induced warming, there is the increasing acidification of the oceans, which is definitely caused by us through increased solution of CO2, with possible dire effects on the food chain.